NAPAC2022 - List of Keywords (cavity)

Paper	Title	Other Keywords	Page
MOYD3	EIC Transverse Emittance Growth Due to Crab Cavity RF Noise: Estimates and Mitigation	emittance, feedback, simulation, target	6
	T. Mastoridis, P. Fuller, P. Mahvi, Y. Matsumura CalPoly, San Luis Obispo, California, USA
	Funding: This work is partially supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under Award Number DE-SC-0019287. The Electron-Ion Collider (EIC) requires crab cavities to compensate for a 25 mrad crossing angle and achieve maximum luminosity. The crab cavity Radio Frequency (RF) system will inject low levels of noise to the crabbing field, generating transverse emittance growth and potentially limiting luminosity lifetime. In this work, we estimate the transverse emittance growth rate as a function of the Crab Cavity RF noise and quantify RF noise specifications for reasonable performance. Finally, we evaluate the possible mitigation of the RF noise induced emittance growth via a dedicated feedback system.
	Slides MOYD3 [0.223 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOYD3
About •	Received ※ 28 July 2022 — Revised ※ 01 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 04 October 2022
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MOYD5	Tolerances of Crab Dispersion at the Interaction Point in the Hadron Storage Ring of the Electron-Ion Collider	proton, simulation, electron, dynamic-aperture	12
	Y. Luo, J.S. Berg, M. Blaskiewicz, C. Montag, V. Ptitsyn, F.J. Willeke, D. Xu BNL, Upton, New York, USA Y. Hao FRIB, East Lansing, Michigan, USA V.S. Morozov ORNL RAD, Oak Ridge, Tennessee, USA J. Qiang LBNL, Berkeley, California, USA T. Satogata JLab, Newport News, Virginia, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The Electron Ion Collider (EIC) presently under construction at Brookhaven National Laboratory will collide polarized high energy electron beams with hadron beams with luminosity up to 10³⁴ cm^-2 s^-1 in the center mass energy range of 20 to 140 GeV. Due to the detector solenoid in the interaction region, the design horizontal crabbing angle will be coupled to the vertical plane if uncompensated. In this article, we estimate the tolerance of crab dispersion at the interaction point in the EIC Hadron Storage Ring (HSR). Both strong-strong and weak-strong simulations are used. We found that there is a tight tolerance of vertical crabbing angle at the interaction point in the HSR.
	Slides MOYD5 [1.183 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOYD5
About •	Received ※ 01 August 2022 — Accepted ※ 04 August 2022 — Issue date ※ 15 August 2022
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MOYE3	Experiments on a Conduction Cooled Superconducting Radio Frequency Cavity with Field Emission Cathode	niobium, experiment, SRF, accelerating-gradient	16
	Y. Ji, R. Dhuley, C.J. Edwards, J.C.T. Thangaraj Fermilab, Batavia, Illinois, USA V. Korampally, D. Mihalcea, O. Mohsen, P. Piot, I. Salehinia Northern Illinois University, DeKalb, Illinois, USA
	Funding: The project is supported by DOE HEP Accelerator Stewardship award to Fermilab and Northern Illinois University To achieve Ampere-class electron beam accelerators the pulse delivery rate need to be much higher than the typical photo injector repetition rate of the order of a few kilohertz. We propose here an injector which can, in principle, generate electron bunches at the same rate as the operating RF frequency. A conduction-cooled superconducting radio frequency (SRF) cavity operating in the CW mode and housing a field emission element at its region of high axial electric field can be a viable method of generating high-repetition-rate electron bunches. In this paper, we report the development and experiments on a conduction-cooled Nb₃Sn cavity with a niobium rod intended as a field emitter support. The initial experiments demonstrate ~0.4 MV/m average accelerating gradient, which is equivalent of peak gradient of 3.2 MV/m. The measured RF cavity quality factor is 1.4 × 10⁸ slightly above our goal. The achieved field gradient is limited by the relatively low input RF power and by the poor coupling between the external power supply and the RF cavity. With ideal coupling the field gradient can be as high as 0.6 MV/m still below our goal of about 1 MV/m
	Slides MOYE3 [1.444 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOYE3
About •	Received ※ 01 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 30 September 2022
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MOYE5	In Situ Plasma Processing of Superconducting Cavities at JLab	plasma, cryomodule, HOM, radiation	22
	T. Powers, N.C. Brock, T.D. Ganey JLab, Newport News, Virginia, USA
	Jefferson Lab has an ongoing R&D program in plasma processing which is close to going into production processing in the CEBAF accelerator. Plasma processing is a common technique for removing hydrocarbons from surfaces, which increases the work function and reduces the secondary emission coefficient. Unlike helium processing which relies on ion bombardment of the field emitters, plasma processing uses free oxygen produced in the plasma to break down the hydrocarbons on the surface of the cavity. The initial focus of the effort was processing C100 cavities by injecting RF power into the HOM coupler ports. Results from processing cryomodule in the cryomodule test bunker as well as vertical test results will be presented. We plan to start processing cryomodules in the CEBAF tunnel within the next year. The goal will be to improve the operational gradients and the energy margin of the linacs. This work will describe the systems and methods used at JLAB for processing cavities using an argon oxygen gas mixture. Before and after plasma processing results will also be presented.
	Slides MOYE5 [2.679 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOYE5
About •	Received ※ 01 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 01 October 2022
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MOZD6	Accelerator Physics Lessons from CBETA, the First Multi-Turn SRF ERL	linac, electron, SRF, photon	41
	K.E. Deitrick JLab, Newport News, Virginia, USA G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The Cornell-BNL ERL Test Accelerator (CBETA) has been designed, constructed, and commissioned in a collaboration between Cornell and BNL. It focuses on energy-saving measures in accelerators, including permanent magnets, energy recovery, and superconductors; it has thus been referred to as a green accelerator. CBETA has become the world’s first Energy Recovery Linac (ERL) that accelerates through multiple turns and then recovers the energy in SRF cavities though multiple decelerating turns. The energy is then available to accelerate more beam. It has also become the first accelerator that operates 7 beams in the same large-energy aperture Fixed Field Alternating-gradient (FFA) lattice. The FFA is constructed of permanent combined function magnets and transports energies of 42, 78, 114, and 150 MeV simultaneously. Accelerator physics lessons from the commissioning period will be described and applications of such an accelerator from hadron cooling to EUV lithography and from nuclear physics to a compact Compton source will be discussed.
	Slides MOZD6 [3.207 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOZD6
About •	Received ※ 23 July 2022 — Revised ※ 27 July 2022 — Accepted ※ 03 August 2022 — Issue date ※ 06 August 2022
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MOZE4	Ceramic Enhanced Accelerator Structure Low Power Test and Designs of High Power and Beam Tests	electron, impedance, accelerating-gradient, simulation	49
	H. Xu, M.R. Bradley, L.D. Duffy, M.A. Holloway, J. Upadhyay LANL, Los Alamos, New Mexico, USA
	Funding: Research was supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory, under project number 20210083ER. A ceramic enhanced accelerator structure (CEAS) uses a concentric ceramic ring placed inside a metallic pillbox cavity to significantly increase the shunt impedance of the cavity. Single cell standing wave CEAS cavities are designed, built, and tested at low power at 5.1 GHz. The results indicate 40% increase in shunt impedance compared to that of a purely metallic pillbox cavity. A beam test setup has been designed to use a single cell CEAS cavity to modulate a 30-keV direct-current (DC) electron beam at an accelerating gradient of 1 to 2 MV/m to verify the beam acceleration capability of the CEAS concept and to study the potential charging effect on the ceramic component during the operation. Another single cell standing wave CEAS cavity has been designed for high power test at 5.7 GHz for the high accelerating gradient capability.
	Slides MOZE4 [1.652 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOZE4
About •	Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 07 October 2022
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MOPA12	Commissioning of HOM Detectors in the First Cryomodule of the LCLS-II Linac	HOM, MMI, alignment, cryomodule	69
	J.A. Diaz Cruz UNM-ECE, Albuquerque, USA B.T. Jacobson, N.R. Neveu, J.P. Sikora SLAC, Menlo Park, California, USA
	Long-range wakefields (LRWs) may cause emittance dilution effects. LWRs are especially unwanted at facilities with low emittance beams like the LCLS-II at SLAC. Dipolar higher-order modes (HOMs) are a set of LRWs that are excited by off-axis beams. Two 4-channel HOM detectors were built to measure the beam-induced HOM signals for TESLA-type superconducting RF (SRF) cavities; they were tested at the Fermilab Accelerator Science and Technology (FAST) facility and are now installed at SLAC. The HOM detectors were designed to investigate LRW effects on the beam and to help with beam alignment. This paper presents preliminary results of HOM measurements at the first cryomodule (CM01) of the LCLS-II linac and describes the relevant hardware and setup of the experiment.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA12
About •	Received ※ 09 August 2022 — Accepted ※ 20 August 2022 — Issue date ※ 31 August 2022
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MOPA21	Effect of Electropolishing on Nitrogen Doped and Undoped Niobium Surfaces	niobium, SRF, factory, superconducting-RF	93
	V. Chouhan, F. Furuta, M. Martinello, T.J. Ring, G. Wu Fermilab, Batavia, Illinois, USA
	Cold electropolishing (EP) of a nitrogen-doped (N-doped) niobium (Nb) superconducting RF (SRF) cavity was found to improve its quality factor. In order to understand the effect of EP temperature on N-doped and undoped surfaces, a systematic EP study was conducted with 2/0 N-doped and heat-treated Nb samples in a beaker. The Nb samples were electropolished at different surface temperatures ranging from 0 to 42 C. The results showed that the doped surface was susceptible to the sample temperature during EP. EP resulted in the surface pitting on the doped samples where the number density of pits increased at a higher temperature. The surface results were compared with the surface of cutouts from a 9-cell cavity which was 2/0 N-doped and electropolished. This paper shows de-tailed surface features of the N-doped and undoped Nb surfaces electropolished at different temperatures.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA21
About •	Received ※ 20 July 2022 — Revised ※ 24 July 2022 — Accepted ※ 09 August 2022 — Issue date ※ 11 August 2022
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MOPA22	Study on Electropolishing Conditions for 650 MHz Niobium SRF Cavity	cathode, SRF, niobium, power-supply	97
	V. Chouhan, D.J. Bice, F. Furuta, M. Martinello, M.K. Ng, H. Park, T.J. Ring, G. Wu Fermilab, Batavia, Illinois, USA B.M. Guilfoyle, M.P. Kelly, T. Reid ANL, Lemont, Illinois, USA
	The PIP II linear accelerator includes different types of niobium SRF cavities including 650 MHz elliptical low (0.61) and high (0.92) beta cavities. The elliptical cavity surface is processed with the electropolishing method. The elliptical cavities especially the low-beta 650 MHz cavities showed a rough equator surface after the EP was performed with the standard EP conditions. This work was focused to study the effect of different EP parameters, including cathode surface area, temperature and voltage, and optimize them to improve the cavity surface.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA22
About •	Received ※ 02 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 03 September 2022
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MOPA23	Tests of the Extended Range SRF Cavity Tuners for the LCLS-II HE Project	operation, cryomodule, SRF, vacuum	100
	C. Contreras-Martinez, T.T. Arkan, A.T. Cravatta, B.D. Hartsell, J.A. Kaluzny, T.N. Khabiboulline, Y.M. Pischalnikov, S. Posen, G.V. Romanov, J.C. Yun Fermilab, Batavia, Illinois, USA
	The LCLS-II HE superconducting linac will produce multi-energy beams by supporting multiple undulator lines simultaneously. This could be achieved by using the cavity SRF tuner in the off-frequency detune mode. This off-frequency operation method was tested in the verification cryomodule (vCM) and CM 1 at Fermilab at 2 K. In both cases, the tuners achieved a frequency shift of -565±80 kHz. This study will discuss cavity frequency during each step as it is being assembled in the cryomodule string and finally when it is being tested at 2 K. Tracking the cavity frequency helped enable the tuners to reach this large frequency shift. The specific procedures of tuner setting during assembly will be presented.
	Poster MOPA23 [0.654 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA23
About •	Received ※ 03 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 19 August 2022 — Issue date ※ 31 August 2022
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MOPA24	LCLS-II and HE Cryomodule Microphonics at CMTF at Fermilab	cryomodule, cryogenics, SRF, niobium	103
	C. Contreras-Martinez, B.E. Chase, A.T. Cravatta, J.A. Einstein-Curtis, E.R. Harms, J.P. Holzbauer, J.N. Makara, S. Posen, R. Wang Fermilab, Batavia, Illinois, USA L.R. Doolittle LBNL, Berkeley, California, USA
	Microphonics causes the cavity to detune. This study discusses the microphonics of 16 cryomodules, 14 for LCLS-II and 2 for LCLS-II HE tested at CMTF. The peak detuning, as well as the RMS detuning for each cryomodule, will be discussed. For each cryomodule, the data was taken with enough soaking time to prevent any thermalization effects which can show up in the detuning. Each data capture taken was 30 minutes or longer and sampled at 1 kHz.
	Poster MOPA24 [1.428 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA24
About •	Received ※ 03 August 2022 — Revised ※ 10 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 20 September 2022
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MOPA25	Simulated Lorentz Force Detuning Compensation with a Double Lever Tuner on a Dressed ILC/1.3 GHz Cavity at Room Temperature	controls, flattop, resonance, SRF	106
	C. Contreras-Martinez, Y.M. Pischalnikov, J.C. Yun Fermilab, Batavia, Illinois, USA
	Pulsed SRF linacs with high accelerating gradients experience large frequency shifts caused by Lorentz force detuning (LFD). A piezoelectric actuator with a resonance control algorithm can maintain the cavity frequency at the nominal level thus reducing the RF power. This study uses a double lever tuner with a piezoelectric actuator for compensation and another piezoelectric actuator to simulate the effects of the Lorentz force pulse. A double lever tuner has an advantage by increasing the stiffness of the cavity-tuner system thus reducing the effects of LFD. The tests are conducted at room temperature and with a dressed 1.3 GHz 9-cell cavity.
	Poster MOPA25 [0.931 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA25
About •	Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 13 August 2022
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MOPA27	Validation of the 650 MHz SRF Tuner on the Low and High Beta Cavities for PIP-II at 2 K	SRF, linac, operation, proton	109
	C. Contreras-Martinez, S.K. Chandrasekaran, S. Cheban, G.V. Eremeev, I.V. Gonin, T.N. Khabiboulline, Y.M. Pischalnikov, O.V. Prokofiev, A.I. Sukhanov, J.C. Yun Fermilab, Batavia, Illinois, USA
	The PIP-II linac will include thirty-six B_G=0.61 and twenty-four B_G=0.92 650 MHz 5 cell elliptical SRF cavities. Each cavity will be equipped with a tuning system consisting of a double lever slow tuner for coarse frequency tuning and a piezoelectric actuator for fine frequency tuning. The same tuner will be used for both the B_G=0.61 and B_G=0.92 cavities. Results of testing the cavity-tuner system for the B_G=0.61 will be presented for the first time.
	Poster MOPA27 [0.782 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA27
About •	Received ※ 03 August 2022 — Revised ※ 10 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 04 October 2022
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MOPA30	LCLS-II BCS Average Current Monitor	electron, hardware, MMI, LLRF	120
	N.M. Ludlow, T.L. Allison, J.P. Sikora, J.J. Welch SLAC, Menlo Park, California, USA
	LCLS-II is a 4th generation light source at the SLAC National Accelerator Laboratory. LCLS-II will accelerate a 30 µA electron beam with a 1 MHz bunch rate with a new superconducting Continuous Waveform (CW) RF accelerator. The Average Current Monitor (ACM) is part of the Beam Containment System (BCS) for the LCLS-II accelerator. The Beam Containment System is a safety system that provides paths to safely shut the accelerator beam off under a variety of conditions. The Average Current Monitor is a beam diagnostic within the BCS that is used to verify that the accelerator is producing the appropriate current level and to limit beam power to allowed values to protect the machine and beam dumps. The average beam current is obtained by measuring the power level induced by the beam in a low Q cavity. By knowing the Q, the beta, and the coupling of the cavity, the instantaneous charge can be calculated, then integrating the instantaneous charge over one millisecond will yield the average current. This paper will discuss progress in the checkout process of the ACM LLRF hardware leading to LCLS-II commissioning.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA30
About •	Received ※ 16 July 2022 — Revised ※ 05 August 2022 — Accepted ※ 24 August 2022 — Issue date ※ 06 October 2022
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MOPA36	Optimization of Superconducting Linac for Proton Improvement Plan-II (PIP-II)	emittance, linac, quadrupole, solenoid	132
	A. Pathak, E. Pozdeyev Fermilab, Batavia, Illinois, USA
	PIP-II is an essential upgrade of the Fermilab complex that will enable the world’s most intense high-energy beam of neutrinos for the international Deep Underground Neutrino Experiment at LBNF and support a broad physics program at Fermilab. Ultimately, the PIP-II superconducting linac will be capable of accelerating the H⁻ CW beam to 800 MeV with an average power of 1.6 MW. To operate the linac with such high power, beam losses and beam emittance growth must be tightly controlled. In this paper, we present the results of global optimization of the Linac options towards a robust and efficient physics design for the superconducting section of the PIP-II linac. We also investigate the impact of the nonlinear field of the dipole correctors on the beam quality and derive the requirement on the field quality using statistical analysis. Finally, we assess the need to correct the quadrupole focusing produced by Half Wave, and Single Spoke accelerating cavities. We assess the feasibility of controlling the beam coupling in the machine by changing the polarity of the field of Linac focusing solenoids
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA36
About •	Received ※ 02 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 01 October 2022
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MOPA38	Accelerated Lifetime Test of the SRF Dressed Cavity/Tuner System for the LCLS II HE Project	operation, SRF, vacuum, LabView	136
	Y.M. Pischalnikov, T.T. Arkan, C. Contreras-Martinez, B.D. Hartsell, J.A. Kaluzny, Y.M. Orlov, R.V. Pilipenko, J.C. Yun Fermilab, Batavia, Illinois, USA W. Lahmadi Wahid Lahmadi, Williston, USA
	The off-frequency detune method is being considered for application in the LCLS-II-HE superconducting linac to produce multi-energy electron beams for supporting multiple undulator lines simultaneously. Design of the tuner has been changed to deliver roughly 3 times larger frequency tuning range. Working requirements for off-frequency operation (OFO) state that cavities be tuned at least twice a month. This specification requires the increase of the tuner longevity by 30 times compared with LCLS-II demands. Accelerated longevity tests of the LCLS-II HE dressed cavity with tuner were conducted at FNAL’s HTS. Detail analysis of wearing and impacts on performances of the tuner’s piezo and stepper motor actuators will be presented. Additionally, results of longevity testing of the dressed cavity bellow, when cooled down to 2 K and compressed by 2.6 mm for roughly 2000 cycles, will be presented.
	Poster MOPA38 [3.026 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA38
About •	Received ※ 29 July 2022 — Revised ※ 06 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 11 August 2022
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MOPA59	Prediction of Gaseous Breakdown for Plasma Cleaning of RF Cavities	simulation, plasma, electron, electronics	174
	S.A. Ahmed Ansys, Inc., Canonsburg, USA
	The quest for a high accelerating gradient in superconducting radio frequency cavity attracted scientists to adopt the plasma cleaning technology. Generating an efficient plasma inside a complex cavity structure for a desired frequency, gas types, and pressure for a given temperature is a challenge. The onset of discharge can be obtained from the well-known Paschen curve. Setting up an experiment is expensive and time-consuming, which may lead to a significant delay in the project. A high-fidelity computer simulation, modeling an arbitrary geometry and tracking the Paschen curve in a complex electromagnetic environment is therefore necessary. Ansys HFSS through its Finite Element Mesh (FEM) for the full-wave EM simulations combined with the electron impact ionization of gases enables the successful prediction of plasma breakdown for an arbitrary configuration for a wide frequency band and variety of gases. A comprehensive study will be demonstrated at the conference. The author like to thank Robert Chao for the valuable discussions and his efforts in developing this capability in the Ansys Electronics Desktop.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA59
About •	Received ※ 01 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 19 August 2022
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MOPA60	HFSS Enables Multipaction Analysis of High Power RF/Microwave Components	multipactoring, electron, simulation, vacuum	176
	S.A. Ahmed Ansys, Inc., Canonsburg, USA
	The radiofrequency (RF) components in particle accelerators operated under a vacuum and driven by high RF power may be prone to electron multipaction ’ an RF triggered electron resonance phenomenon causing malfunction or complete breakdown. Therefore, exploring the design challenges of vacuum RF windows, cavities, and other devices for the electron multipaction becomes necessary. Setting up an experiment to mitigate the failure of RF devices is expensive and time-consuming, which may cause a significant delay in the project. Therefore, a high-fidelity computer simulation modeling the arbitrary geometry and tracking the particles (electrons) in a complex electromagnetic environment is desirable. Ansys HFSS through Finite Element Mesh (FEM) for the full-wave RF simulation combined with the particle-in-cell (PIC) technique for tracking particles in EM fields; enables the engineers/physicist successful prediction of system failure against the electron multipaction. This paper will demonstrate the workflow of the HFSS multipaction analysis. The author like to thank Robert Chao for the valuable discussions and his efforts in developing this capability in the Ansys Electronics Desktop.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA60
About •	Received ※ 03 August 2022 — Revised ※ 13 August 2022 — Accepted ※ 26 August 2022 — Issue date ※ 06 October 2022
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MOPA67	Examining the Effects of Oxygen Doping on SRF Cavity Performance	SRF, niobium, ECR, radio-frequency	196
	H. Hu, Y.K. Kim University of Chicago, Chicago, Illinois, USA D. Bafia Fermilab, Batavia, Illinois, USA
	Superconducting radiofrequency (SRF) cavities are resonators with extremely low surface resistance that enable accelerating cavities to have extremely high quality factors (Q₀). High (Q₀) decreases the capital required to keep accelerators cold by reducing power loss. The performance of SRF cavities is largely governed by the surface composition of the first 100 nm of the cavity surface. Impurities such as oxygen and nitrogen have been observed to yield high Q₀, but their precise roles are still being studied. Here, we compare the performance of cavities doped with nitrogen and oxygen in terms of fundamental material properties to understand how these impurities affect performance. This enables us to have further insight into the underlying mechanisms that enable these surface treatments to yield high Q₀ performance.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA67
About •	Received ※ 02 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 03 October 2022
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MOPA72	Preliminary Tests and Beam Dynamics Simulations of a Straight-Merger Beamline	dipole, experiment, simulation, electron	206
	A.A. Al Marzouk, P. Piot, T. Xu Northern Illinois University, DeKalb, Illinois, USA S.V. Benson, K.E. Deitrick, J. Guo, A. Hutton, G.-T. Park, S. Wang JLab, Newport News, Virginia, USA D.S. Doran, G. Ha, P. Piot, J.G. Power, C. Whiteford, E.E. Wisniewski ANL, Lemont, Illinois, USA C.E. Mitchell, J. Qiang, R.D. Ryne LBNL, Berkeley, California, USA
	Funding: NSF award PHY-1549132 to Cornell University and NIU, U.S. DOE contract DE-AC02-06CH11357 with ANL and DE-AC05-06OR23177 with JLAB. Beamlines capable of merging beams with different energies are critical to many applications related to advanced accelerator concepts and energy-recovery linacs (ERLs). In an ERL, a low-energy "fresh" bright bunch is generally injected into a superconducting linac for acceleration using the fields established by a decelerated "spent" beam traveling on the same axis. A straight-merger system composed of a selecting cavity with a superimposed dipole magnet was proposed and recently test at AWA. This paper reports on the experimental results obtained so far along with detailed beam dynamics investigations of the merger concept and its ability to conserve the beam brightness associated with the fresh bunch.
	Poster MOPA72 [1.659 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA72
About •	Received ※ 11 August 2022 — Accepted ※ 13 August 2022 — Issue date ※ 02 October 2022
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MOPA83	Automation of Superconducting Cavity and Superconducting Magnet Operation for FRIB	operation, linac, solenoid, cryomodule	239
	W. Chang, Y. Choi, X.-J. Du, W. Hartung, S.H. Kim, T. Konomi, S.R. Kunjir, H. Nguyen, J.T. Popielarski, K. Saito, T. Xu, S. Zhao FRIB, East Lansing, Michigan, USA
	The superconducting (SC) driver linac for the Facility for Rare Isotope Beams (FRIB) is a heavy-ion accelerator that accelerate ions to 200 MeV per nucleon. The linac has 46 cryomodules that contain 324 SC cavities and 69 SC solenoid packages. For linac operation with high availability and high reliability, automation is essential for such tasks as fast device turn-on/off, fast recovery from trips, and real-time monitoring of operational performance. We have implemented several automation algorithms, including one-button turn-on/off of SC cavities and SC magnets; automated degaussing of SC solenoids; mitigation of field emission-induced multipacting during recovery from cavity trips; and real-time monitoring of the cavity field level calibration. The design, development, and operating experience with automation will be presented.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA83
About •	Received ※ 02 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 26 August 2022
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MOPA84	Superconducting Cavity Commissioning for the FRIB Linac	MMI, cryomodule, controls, linac	242
	W. Chang, W. Hartung, S.H. Kim, T. Konomi, S.R. Kunjir, J.T. Popielarski, K. Saito, T. Xu, S. Zhao FRIB, East Lansing, Michigan, USA
	The superconducting driver linac for the Facility for Rare Isotope Beams (FRIB) is a heavy ion accelerator that has 46 cryomodules with 324 superconducting (SC) cavities that accelerate ions to 200 MeV per nucleon. Linac commissioning was done in multiple phases, in parallel with technical installation. Ion beam have now been accelerated to the design energy through the full linac; rare isotopes were first produced in December 2021; and the first user experiment was completed in May 2022. All cryomodules were successfully commissioned. Cryomodule commissioning included establishing the desired cavity fields, measuring field emission X-rays, optimizing the tuner control loops, measuring the cavity dynamic heat load, and confirming the low-level RF control (amplitude and phase stability). Results on cryomodule commissioning and cryomodule performance will be presented.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA84
About •	Received ※ 13 July 2022 — Revised ※ 02 August 2022 — Accepted ※ 13 August 2022 — Issue date ※ 05 September 2022
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MOPA85	Design of a 185.7 MHz Superconducting RF Photoinjector Quarter-Wave Resonator for the LCLS-II-HE Low Emittance Injector	SRF, gun, cathode, electron	245
	S.H. Kim, W. Hartung, T. Konomi, S.J. Miller, M.S. Patil, J.T. Popielarski, K. Saito, T. Xu, T. Xu FRIB, East Lansing, Michigan, USA C. Adolphsen, L. Ge, F. Ji, J.W. Lewellen, L. Xiao SLAC, Menlo Park, California, USA M.P. Kelly, T.B. Petersen, P. Piot ANL, Lemont, Illinois, USA P. Piot Northern Illinois University, DeKalb, Illinois, USA
	Funding: Work supported by the U.S. Department of Energy Contract DE-AC02-76SF00515. A 185.7 MHz superconducting quarter-wave resonator (QWR) was designed for the low emittance injector of the Linac Coherent Light Source high energy upgrade (LCLS-II-HE). The cavity was designed to minimize the risk of cathode efficiency degradation due to multipacting or field emission and to operate with a high RF electric field at the cathode for low electron-beam emittance. Cavity design features include: (1) shaping of the cavity wall to reduce the strength of the low-field coaxial multipacting barrier; (2) four ports for electropolishing and high-pressure water rinsing; and (3) a fundamental power coupler (FPC) port located away from the accelerating gap. The design is oriented toward minimizing the risk of particulate contamination and avoid harmful dipole components in the RF field. The ANL 162 MHz FPC design for PIP-II is being adapted for the gun cavity. We will present the RF design of the cavity integrated with the FPC.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA85
About •	Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 30 August 2022
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MOPA86	Conditioning of Low-Field Multipacting Barriers in Superconducting Quarter-Wave Resonators	coupling, multipactoring, cryomodule, electron	249
	S.H. Kim, W. Chang, W. Hartung, J.T. Popielarski, T. Xu FRIB, East Lansing, Michigan, USA
	Funding: This is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661, the State of Michigan and Michigan State University. Multipacting (MP) barriers are typically observed at very low RF amplitude, at a field 2 to 3 orders of magnitude below the operating gradient, in low-frequency (<~100 MHz), quarter-wave resonators (QWRs). Such barriers may be troublesome, as RF conditioning with a fundamental power coupler (FPC) of typical coupling strength (external Q = 10⁶ to 10⁷) is generally difficult. For the FRIB \beta = 0.085 QWRs (80.5 MHz), the low barrier is observed at an accelerating gradient (E_acc) of ~10 kV/m; the operating E_acc is 5.6 MV/m. Theoretical and simulation studies suggested that the conditioning is difficult due to the relatively low RF power dissipated into multipacting rather than being a problem of the low barrier being stronger than other barriers. We developed a single-stub coaxial FPC matching element for external adjustment of the external Q by one order of magnitude. The matching element provided a significant reduction in the time to condition the low barrier. We will present theoretical and simulation studies of the low MP barrier and experimental results on MP conditioning with the single-stub FPC matching element.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA86
About •	Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 21 August 2022
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MOPA87	Design of the Cathode Stalk for the LCLS-II-HE Low Emittance Injector	cathode, gun, SRF, ISOL	253
	T. Konomi, W. Hartung, S.H. Kim, S.J. Miller, D.G. Morris, J.T. Popielarski, K. Saito, A. Taylor, T. Xu FRIB, East Lansing, Michigan, USA C. Adolphsen, J.W. Lewellen SLAC, Menlo Park, California, USA S. Gatzmaga, P. Murcek, R. Xiang HZDR, Dresden, Germany M.P. Kelly, T.B. Petersen ANL, Lemont, Illinois, USA
	Superconducting radio-frequency (SRF) electron guns are attractive for delivery of beams at a high bunch repetition rate with a high accelerating field. An SRF gun is the most suitable injector for the high-energy upgrade of the Linac Coherent Light Source (LCLS-II-HE), which will produce high-energy X-rays at high repetition rate. An SRF gun is being developed for LCLS-II-HE as a collaborative effort by FRIB, HZDR, ANL, and SLAC. The cavity operating frequency is 185.7 MHz, and the target accelerating field at the photocathode is 30 MV/m. The photocathode is replaceable. The cathode is held by a fixture (’cathode stalk’) that is designed for thermal isolation and particle-free cathode exchange. The stalk must allow for precise alignment of the cathode position, cryogenic or room-temperature cathode operating temperature, and DC bias to inhibit multipacting. We are planning a test of the stalk to confirm that the design meets the requirements for RF power dissipation and biasing. In this presentation, we will describe the cathode stalk design and RF/DC stalk test plan.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA87
About •	Received ※ 04 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 18 August 2022 — Issue date ※ 11 September 2022
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MOPA88	FRIB and UEM LLRF Controller Upgrade	controls, LLRF, FPGA, operation	256
	S.R. Kunjir, E. Bernal, D.G. Morris, S. Zhao FRIB, East Lansing, Michigan, USA C.-Y. Ruan MSU, East Lansing, Michigan, USA
	Funding: Supported by the U.S. DOE Office of Science under Cooperative Agreement DE-SC0000661, the State of Michigan, Michigan State University and U.S. National Science Foundation grant DMR-1625181. The Facility for Rare Isotope Beams (FRIB) is developing a 644 MHz superconducting (SC) cavity for a future upgrade project. The current low level radio frequency (LLRF) controller at FRIB is not able to operate at 644 MHz. The Ultrafast Electron Microscope (UEM) laboratory within the Department of Physics at Michigan State University designed an LLRF controller based on analog RF components to operate a 1.013 GHz room temperature (RT) cavity. With requirements for improved stability, performance and user controls there was a need to upgrade the analog LLRF controller. The FRIB radio frequency (RF) group designed, developed and fabricated a new digital LLRF controller, with high-speed serial interface between system on chip field programmable gate array and fast data converters and capable of high frequency direct sampling, to meet the requirements of 644 MHz SC cavity and 1.013 GHz UEM RT cavity. This paper gives an overview of the upgraded digital LLRF controller, its features, improvements and preliminary test results.
	Poster MOPA88 [2.818 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA88
About •	Received ※ 01 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 04 August 2022 — Issue date ※ 16 August 2022
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MOPA91	Plasma Processing of Superconducting Quarter-Wave Resonators Using a Higher-Order Mode	plasma, SRF, cryomodule, HOM	267
	W. Hartung, W. Chang, K. Elliott, S.H. Kim, T. Konomi, J.T. Popielarski, K. Saito, T. Xu FRIB, East Lansing, Michigan, USA
	The Facility for Rare Isotope Beams (FRIB) is a superconducting ion linac with acceleration provided by 104 quarter-wave resonators (QWRs) and 220 half-wave resonators (HWRs); FRIB user operations began in May 2022. Plasma cleaning is being developed as a method to mitigate possible future degradation of QWR or HWR performance: in-situ plasma cleaning represents an alternative to removal and disassembly of cryomodules for refurbishment of each cavity via repeat etching and rinsing. Initial measurements were done on a QWR and an HWR with room-temperature-matched input couplers to drive the plasma via the fundamental mode. Subsequent plasma cleaning tests were done on two additional FRIB QWRs using the fundamental power coupler (FPC) to drive the plasma. When using the FPC, a higher-order mode (HOM) at 5 times the accelerating mode frequency was used to drive the plasma. Use of the HOM allowed for less mismatch at the FPC and hence lower field in the coupler relative to the cavity. A neon-oxygen gas mixture was used for plasma generation. Before and after cold tests showed a significant reduction in field emission X-rays after plasma cleaning. Results will be presented.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA91
About •	Received ※ 12 August 2022 — Revised ※ 16 August 2022 — Accepted ※ 25 August 2022 — Issue date ※ 16 September 2022
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TUXD6	Dual Radiofrequency Cavity Based Monochromatization for High Resolution Electron Energy Loss Spectroscopy	electron, cathode, simulation, space-charge	278
	A.V. Kulkarni, P.E. Denham, A. Kogar, P. Musumeci UCLA, Los Angeles, USA
	Reducing the energy spread of electron beams can enable breakthrough advances in electron energy loss spectroscopic investigations of solid state samples where characteristic excitations typically have energy scales on the order of meV. In conventional electron sources the energy spread is limited by the emission process and typically on the order of a fraction of an eV. State-of-the-art energy resolution can only be achieved after significant losses in the monochromatization process. Here we propose to take advantage of photoemission from ultrashort laser pulses (~40 fs) so that after a longitudinal phase space manipulation that trades pulse duration for energy spread, the energy spread can be reduced by more than one order of magnitude. The scheme uses two RF cavities to accomplish this goal and can be implemented on a relatively short (~ 1m) beamline. Analytical predictions and results of 3D self consistent beam dynamics simulations are presented to support the findings.
	Slides TUXD6 [1.461 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUXD6
About •	Received ※ 03 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 18 August 2022
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TUPA11	Magnet System for a Compact Microtron Source	microtron, electron, extraction, injection	363
	S.A. Kahn, R.J. Abrams, M.A. Cummings, R.P. Johnson, G.M. Kazakevich Muons, Inc, Illinois, USA
	Funding: Work supported in part by U.S. D.O.E. SBIR grant DE-SC0013795. A microtron can be an effective intense electron source. It can use less RF power than a linac to produce a similar energy because the beam will pass through the RF cavity several times. To produce a high-quality low-emittance beam with a microtron requires a magnetic system with a field uniformity $δ B/B<0.001. Field quality for a compact microtron with fewer turns is more difficult to achieve. In this study we describe the magnet for a compact S-band microtron that will achieve the necessary field requirements. The shaping of the magnet poles and shimming of the magnet iron at the outer extent of the poles will be employed to provide field uniformity. The extraction of the beam will be discussed.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA11
About •	Received ※ 04 August 2022 — Revised ※ 14 August 2022 — Accepted ※ 06 September 2022 — Issue date ※ 08 October 2022
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TUPA13	Affordable, Efficient Injection-Locked Magnetrons for Superconducting Cavities	injection, electron, controls, GUI	366
	M. Popovic, M.A. Cummings, R.P. Johnson, S.A. Kahn, R.R. Lentz, M.L. Neubauer, T. Wynn Muons, Inc, Illinois, USA T. Blassick, J.K. Wessel Richardson Electronics Ltd, Lafox, Illinois, USA
	Funding: DE-SC0022586. Existing magnetrons that are typically used to study methods of control or lifetime improvements for SRF accelerators are built for much different applications such kitchen microwave ovens (1kW, 2.45 GHz) or industrial heating (100 kW, 915 MHz). In this project, Muons, Inc. will work with an industrial partner to develop fast and flexible manufacturing techniques to allow many ideas to be tested for construction variations that enable new phase and amplitude injection locking control methods, longer lifetime, and inexpensive refurbishing resulting in the lowest possible life-cycle costs. In Phase II magnetron sources will be tested on SRF cavities to accelerate an electron beam at JLab. A magnetron operating at 650 MHz will be constructed and tested with our novel patented subcritical voltage operation methods to drive an SRF cavity. The choice of 650 MHz is an optimal frequency for magnetron efficiency. The critical areas of magnetron manufacturing and design affecting life-cycle costs that will be modeled for improvement include: Q_ext, filaments, magnetic field, vane design, and novel control of outgassing.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA13
About •	Received ※ 05 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 23 August 2022
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TUPA15	Development of a CVD System for Next-Generation SRF Cavities	controls, SRF, GUI, vacuum	372
	G. Gaitan, P. Bishop, A.T. Holic, G. Kulina, J. Sears, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA M. Liepe Cornell University, Ithaca, New York, USA B.W. Wendland University of Minnesota, Minnesota, USA
	Funding: This research is funded by the National Science Foundation under Grant No. PHY-1549132, the Center for Bright Beams. Next-generation, thin-film surfaces employing Nb₃Sn, NbN, NbTiN, and other compound superconductors are destined to allow reaching superior RF performance levels in SRF cavities. Optimized, advanced deposition processes are required to enable high-quality films of such materials on large and complex-shaped cavities. For this purpose, Cornell University is developing a remote plasma-enhanced chemical vapor deposition (CVD) system that facilitates coating on complicated geometries with a high deposition rate. This system is based on a high-temperature tube furnace with a clean vacuum and furnace loading system. The use of plasma alongside reacting precursors will significantly reduce the required processing temperature and promote precursor decomposition. The system can also be used for annealing cavities after the CVD process to improve the surface layer. The chlorine precursors have the potential to be corrosive to the equipment and pose specific safety concerns. A MATLAB GUI has been developed to control and monitor the CVD system at Cornell.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA15
About •	Received ※ 14 July 2022 — Revised ※ 08 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 22 August 2022
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TUPA27	Longitudinal Feedback Dynamics in Storage Rings with Small Synchrotron Tunes	feedback, HOM, simulation, synchrotron	405
	R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: This work was supported by U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357. We analyze the dynamics of multibunch longitudinal instabilities including bunch-by-bunch feedback under the assumption that the synchrotron tune is small. We find that increasing the feedback response does not always guarantee stability, even in the ideal case with no noise. As an example, we show that if the growth rate of a cavity-driven mode is of the order of the synchrotron frequency, then there are parameter regions for which the instability cannot be controlled by feedback irrespective of its gain. We verify these calculations with tracking simulations relevant to the APS-U, and find that the dynamics do not depend upon whether the longitudinal feedback relies on phase-sensing or energy-sensing technology. Hence, this choice should be dictated by measurement accuracy and noise considerations.
	Poster TUPA27 [1.180 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA27
About •	Received ※ 26 July 2022 — Revised ※ 05 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 26 August 2022
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TUPA43	Novel RF Phase Detector for Accelerator Applications	detector, controls, LLRF, feedback	446
	J.M. Potter JP Accelerator Works, Los Alamos, New Mexico, USA
	A novel phase detector has been developed that is suitable for use in an rf phase locked loop for locking an rf source to an rf accelerator structure or phase locking the accelerator structure to a fixed or adjustable frequency rf source. It is also useful for fast phase feedback to control the phase of an accelerator rf field. The principle is applicable to a wide range of frequencies and amplitudes. The phase is uniquely and unambiguously determined over 360°, eliminating the need for external phase shifters or phase references. The operation of this phase detector is described in detail. An application is described that uses a DDS-based LLRF source as the rf input to a high-power rf system.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA43
About •	Received ※ 02 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 06 October 2022
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TUPA57	Electromagnetic and Beam Dynamics Modeling of the LANSCE Coupled-Cavity Linac	linac, simulation, emittance, quadrupole	472
	S.S. Kurennoy, Y.K. Batygin, D.V. Gorelov LANL, Los Alamos, New Mexico, USA
	The 800-MeV proton linac at LANSCE consists of a drift-tube linac, which brings the beam to 100 MeV, followed by a coupled-cavity linac (CCL) consisting of 44 modules. Each CCL module contains multiple tanks, and it is fed by a single 805-MHz klystron. CCL tanks are multi-cell blocks of identical re-entrant side-coupled cavities, which are followed by drifts with magnetic quadrupole doublets. Bridge couplers - special cavities displaced from the beam axis - electromagnetically couple CCL tanks over such drifts. We have developed 3D CST models of CCL tanks. Their electromagnetic analysis is performed using MicroWave Studio. Beam dynamics is modeled with Particle Studio for bunch trains with realistic beam distributions using the CST calculated RF fields and quadrupole magnetic fields to determine the output beam parameters. Beam dynamics results are crosschecked with other multi-particle codes.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA57
About •	Received ※ 15 July 2022 — Revised ※ 01 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 19 August 2022
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TUPA58	Iterative Tuning of the Beam Feedforward Controller for LANSCE LINAC Digital Low Level RF Control System	controls, beam-loading, LLRF, neutron	475
	S. Kwon, A.T. Archuleta, L.J. Castellano, M.S. Prokop, C. Rose, P.A. Torrez, P. Van Rooy LANL, Los Alamos, New Mexico, USA
	Funding: USDOE This paper addresses an iterative particle beam phase and amplitude feedforward controller tuning method based on the gradient search approach. The method does not need an a priori plant model as it only needs data collected in previous experimental runs. The controller is implemented on a field programmable gate array (FPGA) equipped with a real-time operating system and a network connection. Data from each RF pulse is collected and sent via the network to the FPGA for processing. The controller tuning is performed between the RF pulses. Once the tuning is performed, the controller parameters are downloaded to the controller in the FPGA and new controller parameters are applied at the upcoming RF pulse
	Poster TUPA58 [0.998 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA58
About •	Received ※ 01 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 07 September 2022
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TUPA59	RF System Upgrade for Low Energy DTL Cavity at LANSCE	controls, DTL, LLRF, MMI	478
	J.T.M. Lyles, R.E. Bratton, T.W. Hall, M. Sanchez Barrueta LANL, Los Alamos, New Mexico, USA
	Funding: Work supported by the United States Department of Energy, National Nuclear Security Agency, under contract 89233218CNA000001. The Los Alamos Neutron Science Center (LANSCE) 100-MeV Drift Tube Linac (DTL) uses four accelerating cavities. In May of 2021, a new RF amplifier system was commissioned to drive the first 4-MeV cavity. It had been powered for 30 years with a triode vacuum tube RF amplifier driven by a tetrode, along with four more vacuum tubes for anode high-voltage modulation. The new amplifier system uses one tetrode amplifier driven by a 20-kW solid state amplifier (SSA) to generate 400 kWp at 201.25 MHz. The tetrode amplifier is protected for reflected power from the DTL by a coaxial circulator. The new installation includes cRio controls and a fast protection and monitoring system capable of reacting to faults within 10 µs. A new digital low-level RF (LLRF) system has been installed that integrates I/Q signal processing, PI feedback, and feedforward controls for beam loading compensation. Issues with LLRF stability were initially encountered due to interaction from thermal-related RF phase changes. After these issues were solved, the final outcome has been a reliable new RF system to complete the overall upgrade of the LANSCE DTL RF power plant.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA59
About •	Received ※ 03 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 12 August 2022
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TUPA69	Improving Cavity Phase Measurements at Los Alamos Neutron Science Center	GUI, LLRF, controls, neutron	493
	P. Van Rooy, A.T. Archuleta, L.J. Castellano, S. Kwon, M.S. Prokop, P.A. Torrez LANL, Los Alamos, New Mexico, USA
	Control stability of the phase and amplitude in the cavity is a significant contributor to beam performance. The ability to measure phase and amplitude of pulsed RF systems at accuracies of ± 0.1 degrees and ± 0.1 percent required for our systems is difficult, and custom-designed circuitry is required. The digital low-level RF upgrade at the Los Alamos Neutron Science Center is continuing to progress with improved cavity phase measurements. The previous generation of the cavity phase and amplitude measurement system has a phase ambiguity, which requires repeated calibrations to ascertain the correct phase direction. The new phase measurement system removes the ambiguity and the need for field calibration while improving the range and precision of the cavity phase measurements. In addition, the new digital low-level RF systems is designed to upgrade the legacy system without significant mechanical, electrical, or cabling changes. Performance data for the new phase measurement system is presented.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA69
About •	Received ※ 02 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 21 August 2022 — Issue date ※ 08 September 2022
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TUPA73	Design and Low Power Test of an Electron Bunching Enhancer Using Electrostatic Potential Depression	electron, simulation, gun, experiment	499
	H. Xu, B.E. Carlsten, Q.R. Marksteiner LANL, Los Alamos, New Mexico, USA B.L. Beaudoin, T.W. Koeth, A. Ting UMD, College Park, Maryland, USA
	Funding: This project was supported by the U.S. Department of Energy Office of Science through the Accelerator Stewardship Program. We present our experimental design and low power test results of a structure for the proof-of-principle demonstration of fast increase of the first harmonic current content in a bunched electron beam, using the technique of electrostatic potential depression (EPD). A primarily bunched electron beam from an inductive output tube (IOT) at 710 MHz first enters an idler cavity, where the longitudinal slope of the beam energy distribution is reversed. The beam then transits through an EPD section implemented by a short beam pipe with a negative high voltage bias, inside which the rate of increase of the first harmonic current is significantly enhanced. An output cavity measures the harmonic current developed inside the beam downstream of the EPD section. Low power test results of the idler and the output cavities agree with the theoretical design.
	Poster TUPA73 [1.307 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA73
About •	Received ※ 29 July 2022 — Accepted ※ 03 August 2022 — Issue date ※ 09 August 2022
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TUPA75	High Gradient Testing Results of the Benchmark a/λ=0.105 Cavity at CERF-NM	GUI, klystron, coupling, MMI	505
	M.R.A. Zuboraj, D.V. Gorelov, T.W. Hall, M.E. Middendorf, D. Rai, E.I. Simakov, T. Tajima LANL, Los Alamos, New Mexico, USA
	Funding: This work was supported by Los Alamos National Laboratory’s Laboratory Directed Research and Development (LDRD) Program. This presentation will report initial results of high gradient testing of two C-band accelerating cavities fabricated at Los Alamos National Laboratory (LANL). At LANL, we commissioned a C-band Engineering Research Facility of New Mexico (CERF-NM) which has unique capability of conditioning and testing accelerating cavities for operation at surface electric fields at the excess of 300 MV/m, powered by a 50 MW, 5.712 GHz Canon klystron. Recently, we fabricated and tested two benchmark copper cavities at CERF-NM. These cavities establish a benchmark for high gradient performance at C-band and the same geometry will be used to provide direct comparison between high gradient performance of cavities fabricated of different alloys and by different fabrication methods. The cavities consist of three cells with one high gradient central cell and two coupling cells on the sides. The ratio of the radius of the coupling iris to the wavelength is a/λ=0.105. This poster will report high gradient test results such as breakdown rates as function of peak surface electric and magnetic fields and pulse heating.
	Poster TUPA75 [0.890 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA75
About •	Received ※ 05 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 01 October 2022
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TUPA77	X-Band Harmonic Longitudinal Phase Space Linearization at the PEGASUS Photoinjector	linac, electron, gun, laser	508
	P.E. Denham, P. Musumeci, A. Ody UCLA, Los Angeles, USA
	Due to the finite bunch length, photoemitted electron beams sample RF-nonlinearities that lead to energy-time correlations along the bunch temporal profile. This is an important effect for all applications where the projected energy spread is important. In particular, for time-resolved single shot electron microscopy, it is critical to keep the beam energy spread below 1·10^-4 to avoid chromatic aberrations in the lenses. Higher harmonic RF cavities can be used to compensate for the RF-induced longitudinal phase space nonlinearities. Start-to-end simulations suggest that this type of compensation can reduce energy spread to the 1·10^-5 level. This work is an experimental study of x-band harmonic linearization of a beam longitudinal phase space at the PEGASUS facility, including developing high-resolution spectrometer diagnostics to verify the scheme.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA77
About •	Received ※ 25 July 2022 — Revised ※ 04 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 10 August 2022
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TUPA80	Cyborg Beamline Development Updates	gun, cathode, cryogenics, simulation	512
	G.E. Lawler, A. Fukasawa, N. Majernik, J.R. Parsons, J.B. Rosenzweig, Y. Sakai UCLA, Los Angeles, California, USA F. Bosco Sapienza University of Rome, Rome, Italy Z. Li, S.G. Tantawi SLAC, Menlo Park, California, USA B. Spataro LNF-INFN, Frascati, Italy
	Funding: This work was supported by the Center for Bright Beams, National Science Foundation Grant No. PHY-1549132 and DOE Contract DE-SC0020409. Xray free electron laser (XFEL) facilities in their current form are large, costly to maintain, and inaccessible due to their minimal supply and high demand. It is then advantageous to consider miniaturizing XFELs through a variety of means. We hope to increase beam brightness from the photoinjector via high gradient operation (>120 MV/m) and cryogenic temperature operation at the cathode (<77K). To this end we have designed and fabricated our new CrYogenic Brightness-Optimized Radiofrequency Gun (CYBGORG). The photogun is 0.5 cell so much less complicated than our eventual 1.6 cell photoinjector. It will serve as a prototype and test bed for cathode studies in a new cryogenic and very high gradient regime. We present here the fabricated structure, progress towards commissioning, and beamline simulations.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA80
About •	Received ※ 02 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 09 October 2022
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TUPA81	Design of a High-Power RF Breakdown Test for a Cryocooled C-Band Copper Structure	cryogenics, GUI, distributed, electron	516
	G.E. Lawler, A. Fukasawa, J.R. Parsons, J.B. Rosenzweig UCLA, Los Angeles, California, USA Z. Li, S.G. Tantawi SLAC, Menlo Park, California, USA A. Mostacci Sapienza University of Rome, Rome, Italy E.I. Simakov, T. Tajima LANL, Los Alamos, New Mexico, USA B. Spataro LNF-INFN, Frascati, Italy
	Funding: This work was supported by the DOE Contract DE-SC0020409. High-gradient RF structures capable of maintaining gradients in excess of 250 MV/m are critical in several concepts for future electron accelerators. Concepts such as the ultra-compact free electron laser (UC-XFEL) and the Cool Copper Collider (C3) plan to obtain these gradients through the cryogenic operation (<77K) of normal conducting copper cavities. Breakdown rates, the most significant gradient limitation, are significantly reduced at these low temperatures, but the precise physics is complex and involves many interacting effects. High-power RF breakdown measurements at cryogenic temperatures are needed at the less explored C-band frequency (5.712 GHz), which is of great interest for the aforementioned concepts. On behalf of a large collaboration of UCLA, SLAC, LANL, and INFN, the first C-band cryogenic breakdown measurements will be made using a LANL RF test infrastructure. The 2-cell geometry designed for testing will be modifications of the distributed coupled reentrant design used to efficiently power the cells while staying below the limiting values of peak surface electric and magnetic fields.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA81
About •	Received ※ 29 July 2022 — Accepted ※ 02 August 2022 — Issue date ※ 08 August 2022
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WEYE2	Upgrade of the FRIB ReAccelerator	cryomodule, experiment, MMI, ion-source	572
	A.C.C. Villari, B. Arend, G. Bollen, D.B. Crisp, K.D. Davidson, K. Fukushima, A.I. Henriques, K. Holland, S.H. Kim, A. Lapierre, Y. Liu, T. Maruta, D.G. Morris, S. Nash, P.N. Ostroumov, A.S. Plastun, J. Priller, S. Schwarz, B.M. Sherrill, M. Steiner, C. Sumithrarachchi, R. Walker, T. Zhang, Q. Zhao FRIB, East Lansing, Michigan, USA
	Funding: Work supported by the NSF under grant PHY15-65546 and DOE-SC under award number DE-SC0000661 The reaccelerator facility at FRIB was upgraded to provide new science opportunities. The upgrade included a new ion source to produce stable and long livied rare isotopes in a batch mode, a new room-temperature rebuncher, a new β = 0.085 quarter-wave-resonator cryomodule to increase the beam energy from 3 MeV/u to 6 MeV/u for ions with a charge-to-mass ratio of 1/4, and a new experimental vault with beamlines.
	Slides WEYE2 [4.220 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEYE2
About •	Received ※ 13 July 2022 — Revised ※ 01 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 10 August 2022
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WEZD6	Manufacturing the Harmonic Kicker Cavity Prototype for the Electron-Ion Collider	kicker, electron, collider, MMI	601
	S.A. Overstreet, M.W. Bruker, G.A. Grose, J. Guo, J. Henry, G.-T. Park, R.A. Rimmer, H. Wang, R.S. Williams JLab, Newport News, Virginia, USA
	Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 High-bunch-frequency beam-separation schemes, such as the injection scheme proposed for the Rapid Cycling Synchrotron at the Electron-Ion Collider, demand rise and fall times an order of magnitude below what can realistically be accomplished with a stripline kicker. Nanosecond-time-scale kick waveforms can instead be obtained by Fourier synthesis in a harmonically resonant quarter-wave radio-frequency cavity which is optimized for high shunt impedance. Originally developed for the Jefferson Lab Electron-Ion Collider (JLEIC) Circulator Cooler Ring, a hypothetical 11-pass ring driven by an energy-recovery linac at Jefferson Lab, our high-power prototype of such a harmonic kicker cavity, which operates at five modes at the same time, will demonstrate the viability of this concept with a beam test at Jefferson Lab. As the geometry of the cavity, tight mechanical tolerances, and number of ports complicate the design and manufacturing process, special care must be given to the order of the manufacturing steps. We present our experiences with the manufacturability of the present design, lessons learned, and first RF test results from the prototype.
	Slides WEZD6 [12.312 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZD6
About •	Received ※ 04 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 18 August 2022 — Issue date ※ 31 August 2022
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WEZE3	Compact, High-Power Superconducting Electron Linear Accelerators for MW Industrial Applications	electron, SRF, vacuum, gun	604
	J.C.T. Thangaraj, R. Dhuley Fermilab, Batavia, Illinois, USA
	Fermilab has developed a novel concept for an industrial electron linac using Nb₃Sn coating technology and conduction cooling. We will show the range of multi-cavity linac designs targeted toward various applications. We will also discuss technology development status with results on conduction cooling of SRF cavities based on cryocoolers, which removes the need for liquid Helium, thus making SRF technology accessible to industrial applications. These conduction-cooled linacs can generate electron beam energies up to 10 MeV in continuous-wave operation and can reach higher power (>=1 MW) by combing several modules. Compact and light enough to mount on mobile platforms, our machine is anticipated to enable new in-situ environmental remediation applications such as waste-water treatment for urban areas, X-ray medical device sterilization, and innovative pavement applications. We also show cost-economics and key R&D areas that much be addressed for a practical machine.
	Slides WEZE3 [3.811 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZE3
About •	Received ※ 02 August 2022 — Revised ※ 12 August 2022 — Accepted ※ 13 August 2022 — Issue date ※ 30 August 2022
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WEZE4	First High-Gradient Results of UED/UEM SRF Gun at Cryogenic Temperatures	gun, SRF, accelerating-gradient, cryogenics	607
	R.A. Kostin, C. Jing Euclid Beamlabs, Bolingbrook, USA D.J. Bice, T.N. Khabiboulline, S. Posen Fermilab, Batavia, Illinois, USA
	Funding: The project is funded by DOE SBIR #DE-SC0018621 Benefiting from the rapid progress on RF photogun technologies in the past two decades, the development of MeV range ultrafast electron diffraction/microscopy (UED and UEM) has been identified as an enabling instrumentation. UEM or UED use low power electron beams with modest energies of a few MeV to study ultrafast phenomena in a variety of novel and exotic materials. SRF photoguns become a promising candidate to produce highly stable electrons for UEM/UED applications because of the ultrahigh shot-to-shot stability compared to room temperature RF photoguns. SRF technology was prohibitively expensive for industrial use until two recent advancements: Nb₃Sn and conduction cooling. The use of Nb₃Sn allows to operate SRF cavities at higher temperatures (4K) with low power dissipation which is within the reach of commercially available closed-cycle cryocoolers. Euclid is developing a continuous wave (CW), 1.5-cell, MeV-scale SRF conduction cooled photogun operating at 1.3 GHz. In this paper, we present first high gradient results of the gun conducted in liquid helium.
	Slides WEZE4 [2.817 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZE4
About •	Received ※ 05 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 29 September 2022
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WEZE5	Magnetic Flux Expulsion in Superconducting Radio-Frequency Niobium Cavities Made from Cold Worked Niobium	SRF, niobium, radio-frequency, ECR	611
	B.D. Khanal ODU, Norfolk, Virginia, USA S. Balachandran, P.J. Lee NHMFL, Tallahassee, Florida, USA S. Chetri ASC, Tallahassee, Florida, USA P. Dhakal JLab, Newport News, Virginia, USA
	Trapped residual magnetic field during the cool down of superconducting radio frequency (SRF) cavities is one of the primary sources of RF residual losses leading to lower quality factor. Historically, SRF cavities have been fabricated from high purity fine grain niobium with grain size ~50 to 100 µm as well as large grain with grain size of the order of few centimeters. Non-uniform recrystallization of fine-grain Nb cavities after the post fabrication heat treatment leads to higher flux trapping during the cool down, and hence the lower quality factor. We fabricated two 1.3 GHz single cell cavities from cold-worked niobium from different vendors and processed along with cavities made from SRF grade Nb. The flux expulsion and flux trapping sensitivity were measured after successive heat treatments in the range 800 to 1000°C. The flux expulsion from cold-worked fine-grain Nb cavities improves after 800°C/3h heat treatments and it becomes similar to that of standard fine-grain Nb cavities when the heat treatment temperature is higher than 900°C.
	Slides WEZE5 [2.029 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZE5
About •	Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 31 August 2022
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WEPA01	Beam Dynamics Optimization of a Low Emittance Photoinjector Without Buncher Cavities	emittance, electron, cathode, gun	615
	J. Qiang LBNL, Berkeley, California, USA F. Ji, T.O. Raubenheimer SLAC, Menlo Park, California, USA
	The photoinjector plays an important role in generating high brightness low emittance electron beam for x-ray free electron laser applications. In this paper, we report on beam dynamics optimization study of a low emittance photoinjector based on a proposed superconducting gun without including any buncher cavities. Multi-objective optimization with self-consistent beam dynamics simulations was employed to attain the optimal Pareto front.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA01
About •	Received ※ 02 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 11 September 2022
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WEPA02	Beam Dynamics Studies on a Low Emittance Injector for LCLS-II-HE	emittance, cathode, gun, solenoid	619
	F. Ji, C. Adolphsen, R. Coy, L. Ge, C.E. Mayes, T.O. Raubenheimer, L. Xiao SLAC, Menlo Park, California, USA J. Qiang LBNL, Berkeley, California, USA
	The SLAC High Energy upgrade of LCLS-II (LCLS-II-HE) will double the beam energy to 8 GeV, increasing the XFEL photon energy reach to about 13 keV. The energy reach can be extended to 20 keV if the beam emittance can be halved, which requires a higher gradient electron gun with a lower intrinsic emittance photocathode. To this end, the Low Emittance Injector (LEI) will be built that will run parallel to the existing LCLS-II Injector. The LEI design will be based on a state-of-the-art SRF gun with a 30 MV/m cathode gradient. The main goal is to produce transverse beam emittances of 0.1 mm-mrad for 100 pC bunch charges. This paper describes the beam dynamics studies on the design of the LEI including the simulations and multi-objective genetic algorithm (MOGA) optimizations. Performance with different injector layouts, cathode gradients, bunch charges and cathode mean transverse energies (MTEs) will be presented.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA02
About •	Received ※ 02 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 17 August 2022
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WEPA03	Status of the SLAC/MSU SRF Gun Development Project	cathode, gun, SRF, cryomodule	623
	J.W. Lewellen, C. Adolphsen, R. Coy, L. Ge, F. Ji, M.J. Murphy, L. Xiao SLAC, Menlo Park, California, USA A. Arnold, S. Gatzmaga, P. Murcek, R. Xiang HZDR, Dresden, Germany Y. Choi, C. Compton, X.-J. Du, D.B. Greene, W. Hartung, S.H. Kim, T. Konomi, S.J. Miller, D.G. Morris, M.S. Patil, J.T. Popielarski, L. Popielarski, K. Saito, T. Xu FRIB, East Lansing, Michigan, USA M.P. Kelly, T.B. Petersen ANL, Lemont, Illinois, USA
	Funding: US Department of Energy. The LCLS-II-HE project at SLAC is intended to increase the photon energy reach of the LCLS-II FEL to at least 20 keV. In addition to upgrading the undulator system, and increasing the electron beam energy to 8 GeV, the project will also construct a low-emittance injector (LEI) in a new tunnel. To achieve the LEI emittance goals, a low-MTE photocathode will be required, as will on-cathode electric fields up to 50% higher than those achievable in the current LCLS-II photoinjector. The beam source for the LEI will be based around a superconducting quarterwave cavity resonant at 185.7 MHz. A prototype gun is currently being designed and fabricated at the Facility for Rare Isotope Beams (FRIB) at Michigan State University. This paper presents the performance goals for the new gun design, an overview of the prototype development effort, current status, and future plans including fabrication of a "production" gun for the LEI.
	Poster WEPA03 [4.510 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA03
About •	Received ※ 21 July 2022 — Revised ※ 28 July 2022 — Accepted ※ 08 August 2022 — Issue date ※ 11 August 2022
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WEPA09	A Parallel Automatic Simulation Tool for Cavity Shape Optimization	HOM, simulation, SRF, gun	634
	L. Ge, Z. Li, C.-K. Ng, L. Xiao SLAC, Menlo Park, California, USA M. Beall, B.R. Downie, O. Klaas Simmetrix Inc., Clifton Park, USA
	Funding: U.S. Department of Energy under contract No. DE-SC0018715. We present a parallel automatic shape optimization workflow for designing accelerator cavities. The newly developed 3D parallel optimization tool Opt3P based on discrete adjoint methods is used to determine the optimal accelerator cavity shape with the desired spectral response. Initial and updated models, meshes, and design velocities of design parameters for defining the cavity shape are generated with Simmetrix tools for mesh generation (MeshSim), geometry modification and query (GeomSim), and user interface tools (SimModeler). Two shape optimization examples using this automatic simulation workflow will be presented here. One is the TESLA cavity with higher-order-mode (HOM) couplers and the other is a superconducting rf (SRF) gun. The objective for the TESLA cavity is to minimize HOM damping factors and for the SRF gun to minimize the surface electric and magnetic fields while maintaining its operating mode frequency at a prescribed value. The results demonstrate that the automatic simulation tool allows an efficient shape optimization procedure with minimal manual operations. All simulations were performed on the NERSC supercomputer Cori system for solution speedup.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA09
About •	Received ※ 03 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 08 October 2022
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WEPA10	Determination of LCLS-II Gun-2 Prototype Dimensions	gun, cathode, simulation, vacuum	637
	L. Xiao, C. Adolphsen, E.N. Jongewaard, X. Liu, F. Zhou SLAC, Menlo Park, California, USA
	The LCLS-II spare gun (Gun-2) design is largely based on the existing LCLS-II gun (Gun-1), in which there is significant captured dark current (DC) that originates on the high field copper surface near the cathode plug gap opening. To help suppress DC, the Gun-2 cathode and anode noses and the cathode plug opening are elliptically shaped to minimize the peak surface field for a given cathode gradient. Stainless steel (SS) cathode and anode inserts are used in Gun-2 to further reduce dark current. The RF simulations were performed using a model that includes all the 3D features. The thermal and structural analyses were done to investigate the effects of the air pressure and RF heating. The multi-physics simulation results provided the information needed to compute the overall frequency change from the basic 2D model to the nominal frequency during operation. The Gun-2 cathode-to-anode gap distance will be made 1 mm longer than the nominal gap with the expectation that less than 1 mm will be machined off to meet the target frequency. In this paper, the Gun-2 frequency correction calculations are presented, and the cathode-to-anode gap determination is discussed.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA10
About •	Received ※ 30 July 2022 — Revised ※ 03 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 10 August 2022
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WEPA12	Operational Experience of the New Booster Cryomodule at the Upgraded Injector Test Facility	booster, cryomodule, simulation, experiment	640
	M.W. Bruker, R. Bachimanchi, J.M. Grames, M.D. McCaughan, J. Musson, P.D. Owen, T.E. Plawski, M. Poelker, T. Powers, H. Wang, Y.W. Wang JLab, Newport News, Virginia, USA
	Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. Since the early 1990s, the injector of the CEBAF accelerator at Jefferson Lab has relied on a normal-conducting RF graded-beta capture section to boost the kinetic energy of the electron beam from 100 / 130 keV to 600 keV for subsequent acceleration using a cryomodule housing two superconducting 5-cell cavities similar to those used throughout the accelerator. To simplify the injector design and improve the beam quality, the normal-conducting RF capture section and the cryomodule will be replaced with a new single booster cryomodule employing a superconducting, β = 0.6, 2-cell-cavity capture section and a single, β = 0.97, 7-cell cavity. The Upgraded Injector Test Facility at Jefferson Lab is currently hosting the new cryomodule to evaluate its performance with beam before installation at CEBAF. While demonstrating satisfactory performance of the booster and good agreement with simulations, our beam test results also speak to limitations of accelerator operations in a noisy, thermally unregulated environment.
	Poster WEPA12 [3.726 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA12
About •	Received ※ 03 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 06 September 2022
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WEPA19	HE Production Update at JLab - Introducing an Enhanced Nitrogen Purge for Clean String Assembly	controls, cryomodule, vacuum, hardware	659
	P.D. Owen JLab, Newport News, Virginia, USA
	A major limitation to cryomodule performance is field emission caused by particulates within the superconducting cavities. To reduce contamination of the inner surfaces during assembly in a cleanroom, the whole string can be connected to a purge system, which maintains a constant overpressure of dry, clean nitrogen gas. Following successes of similar systems at XFEL and Fermilab, Jefferson Lab followed this example for the production of LCLS-II HE cryomodules. Implementing this system required new procedures, infrastructure, and hardware, as well as significant testing of the system before production began. This paper will summarize the implemented controls and procedures, including lessons learned from Fermilab, as well as the results of mock-up tests. Based on the latter, the system was used to assemble the first article string in April 2022, and was also used during a rework required due to issues with cold FPC ceramics two months later. The benefits of using a purge system with regards to procedure, time savings, and added flexibility for potential rework have already proven to provide a significant improvement for the production of LCLS-II-HE cryomodules at Jefferson Lab.
	Poster WEPA19 [1.538 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA19
About •	Received ※ 02 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 21 August 2022
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WEPA23	SRF Cavity Instability Detection with Machine Learning at CEBAF	EPICS, SRF, linac, controls	669
	D.L. Turner, R. Bachimanchi, A. Carpenter, J. Latshaw, C. Tennant, L.S. Vidyaratne JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. During the operation of CEBAF, one or more unstable superconducting radio-frequency (SRF) cavities often cause beam loss trips while the unstable cavities themselves do not necessarily trip off. Identifying an unstable cavity out of the hundreds of cavities installed at CEBAF is difficult and time-consuming. The present RF controls for the legacy cavities report at only 1 Hz, which is too slow to detect fast transient instabilities. A fast data acquisition system for the legacy SRF cavities is being developed which samples and reports at 5 kHz to allow for detection of transients. A prototype chassis has been installed and tested in CEBAF. An autoencoder based machine learning model is being developed to identify anomalous SRF cavity behavior. The model is presently being trained on the slow (1 Hz) data that is currently available, and a separate model will be developed and trained using the fast (5 kHz) DAQ data once it becomes available. This paper will discuss the present status of the new fast data acquisition system and results of testing the prototype chassis. This paper will also detail the initial performance metrics of the autoencoder model.
	Poster WEPA23 [1.859 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA23
About •	Received ※ 01 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 24 August 2022
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WEPA25	Field Emission Mitigation in CEBAF SRF Cavities Using Deep Learning	radiation, detector, neutron, linac	676
	K. Ahammed, J. Li ODU, Norfolk, Virginia, USA A. Carpenter, R. Suleiman, C. Tennant, L.S. Vidyaratne JLab, Newport News, Virginia, USA
	Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. The Continuous Electron Beam Accelerator Facility (CEBAF) operates hundreds of superconducting radio frequency (SRF) cavities in its two main linear accelerators. Field emission can occur when the cavities are set to high operating RF gradients and is an ongoing operational challenge. This is especially true in newer, higher gradient SRF cavities. Field emission results in damage to accelerator hardware, generates high levels of neutron and gamma radiation, and has deleterious effects on CEBAF operations. So, field emission reduction is imperative for the reliable, high gradient operation of CEBAF that is required by experimenters. Here we explore the use of deep learning architectures via multilayer perceptron to simultaneously model radiation measurements at multiple detectors in response to arbitrary gradient distributions. These models are trained on collected data and could be used to minimize the radiation production through gradient redistribution. This work builds on previous efforts in developing machine learning (ML) models, and is able to produce similar model performance as our previous ML model without requiring knowledge of the field emission onset for each cavity.
	Poster WEPA25 [1.586 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA25
About •	Received ※ 01 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 20 September 2022
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WEPA26	197 MHz Waveguide Loaded Crabbing Cavity Design for the Electron-Ion Collider	HOM, GUI, impedance, electron	679
	S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA J. Guo, R.A. Rimmer JLab, Newport News, Virginia, USA Z. Li SLAC, Menlo Park, California, USA B.P. Xiao BNL, Upton, New York, USA
	The Electron-Ion Collider will require crabbing systems at both hadron and electron storage rings in order to reach the desired luminosity goal. The 197 MHz crab cavity system is one of the critical rf systems of the col-lider. The crab cavity, based on the rf-dipole design, ex-plores the option of waveguide load damping to suppress the higher order modes and meet the tight impedance specifications. The cavity is designed with compact dog-bone waveguides with transitions to rectangular wave-guides and waveguide loads. This paper presents the compact 197 MHz crab cavity design with waveguide damping and other ancillaries.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA26
About •	Received ※ 08 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 06 September 2022
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WEPA27	Effect of Duration of 120 °C Baking on the Performance of Superconducting Radio Frequency Niobium Cavities	niobium, SRF, radio-frequency, accelerating-gradient	683
	B.D. Khanal ODU, Norfolk, Virginia, USA P. Dhakal JLab, Newport News, Virginia, USA
	Over the last decade much attention was given in increasing the quality factor of superconducting radio frequency (SRF) cavities by impurity doping. Prior to the era of doping, the final cavity processing technique to achieve the high accelerating gradient includes the "in situ" low temperature baking of SRF cavities at temperature ~ 120°C for several hours. Here, we present the results of a series of measurements on 1.3 GHz TESLA shape single-cell cavities with successive low temperature baking at 120°C up to 96 hours. The experimental data were analyzed with available theory of superconductivity to elucidate the effect of the duration of low temperature baking on the superconducting properties of cavity materials as well as the RF performance. In addition, the RF loss related to the trapping of residual magnetic field refereed as flux trapping sensitivity was measured with respect to the duration of 120°C bake.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA27
About •	Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 19 August 2022
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WEPA29	Real-Time Cavity Fault Prediction in CEBAF Using Deep Learning	network, cryomodule, SRF, experiment	687
	M. Rahman, K.M. Iftekharuddin ODU, Norfolk, Virginia, USA A. Carpenter, T.S. McGuckin, C. Tennant, L.S. Vidyaratne JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Data-driven prediction of future faults is a major research area for many industrial applications. In this work, we present a new procedure of real-time fault prediction for superconducting radio-frequency (SRF) cavities at the Continuous Electron Beam Accelerator Facility (CEBAF) using deep learning. CEBAF has been afflicted by frequent downtime caused by SRF cavity faults. We perform fault prediction using pre-fault RF signals from C100-type cryomodules. Using the pre-fault signal information, the new algorithm predicts the type of cavity fault before the actual onset. The early prediction may enable potential mitigation strategies to prevent the fault. In our work, we apply a two-stage fault prediction pipeline. In the first stage, a model distinguishes between faulty and normal signals using a U-Net deep learning architecture. In the second stage of the network, signals flagged as faulty by the first model are classified into one of seven fault types based on learned signatures in the data. Initial results show that our model can successfully predict most fault types 200 ms before onset. We will discuss reasons for poor model performance on specific fault types.
	Poster WEPA29 [1.339 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA29
About •	Received ※ 02 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 17 August 2022
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WEPA30	Nb₃Sn Coating of a 2.6 GHz SRF Cavity by Sputter Deposition Technique	SRF, site, target, plasma	691
	M.S. Shakel, W. Cao, H. Elsayed-Ali, Md.N. Sayeed ODU, Norfolk, Virginia, USA G.V. Eremeev Fermilab, Batavia, Illinois, USA U. Pudasaini, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Funding: Supported by DOE, Office of Accelerator R&D and Production, Contact No. DE-SC0022284, with partial support by DOE, Office of Nuclear Physics DE-AC05-06OR23177, Early Career Award to G. Eremeev. Nb₃Sn is of interest as a coating for SRF cavities due to its higher transition temperature Tc ~18.3 K and superheating field Hsh ~400 mT, both are twice that of Nb. Nb₃Sn coated cavities can achieve high-quality factors at 4 K and can replace the bulk Nb cavities operated at 2 K. A cylindrical magnetron sputtering system was built, commissioned, and used to deposit Nb₃Sn on the inner surface of a 2.6 GHz single-cell Nb cavity. With two identical cylindrical magnetrons, this system can coat a cavity with high symmetry and uniform thickness. Using Nb-Sn multilayer sequential sputtering followed by annealing at 950°C for 3 hours, polycrystalline Nb₃Sn films were first deposited at the equivalent positions of the cavity’s beam tubes and equator. The film’s composition, crystal structure, and morphology were characterized by energy dispersive spectroscopy, X-ray diffraction, and atomic force microscopy. The Tc of the films was measured by the four-point probe method and was 17.61 to 17.76 K. Based on these studies, ~1.2 micron thick Nb₃Sn was deposited inside a 2.6 GHz Nb cavity. We will discuss first results from samples and cavity coatings, and the status of the coating system.
	Poster WEPA30 [1.769 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA30
About •	Received ※ 03 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 22 August 2022
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WEPA31	Lower Temperature Annealing of Vapor Diffused Nb₃Sn for Accelerator Cavities	SRF, superconductivity, experiment, electron	695
	J.K. Tiskumara, J.R. Delayen ODU, Norfolk, Virginia, USA G.V. Eremeev Fermilab, Batavia, Illinois, USA U. Pudasaini JLab, Newport News, Virginia, USA
	Nb₃Sn is a next-generation superconducting material for the accelerator cavities with higher critical temperature and superheating field, both twice compared to Nb. It promises superior performance and higher operating temperature than Nb, resulting in significant cost reduction. So far, the Sn vapor diffusion method is the most preferred and successful technique to coat niobium cavities with Nb₃Sn. Although several post-coating techniques (chemical, electrochemical, mechanical) have been explored to improve the surface quality of the coated surface, an effective process has yet to be found. Since there are only a few studies on the post-coating heat treatment at lower temperatures, we annealed Nb₃Sn-coated samples at 800 C - 1000 C to study the effect of heat treatments on surface properties, primarily aimed at removing surface Sn residues. This paper discusses the systematic surface analysis of coated samples after annealing at temperatures between 850 C and 950 C.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA31
About •	Received ※ 02 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 02 September 2022
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WEPA36	Emittance Growth Due to RF Phase Noise in Crab Cavities	emittance, simulation, collider, betatron	708
	H. Huang, S. Zhao ODU, Norfolk, Virginia, USA F. Lin, V.S. Morozov ORNL RAD, Oak Ridge, Tennessee, USA Y. Luo Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA T. Satogata, Y. Zhang JLab, Newport News, Virginia, USA B.P. Xiao, D. Xu BNL, Upton, New York, USA
	The Electron-Ion Collider (EIC) incorporates beam crabbing to recover geometric luminosity loss from the nonzero crossing angle at the interaction point (IP). It is well-known that crab cavity imperfections can cause growth of colliding beam emittances, thus degrading collider performance. Here we report a particle tracking study to quantify these effects. Presently the study is focused on crab cavity RF phase noise. Simulations were carried out using Bmad. Dependence of emittance growth on phase noise level was obtained which could be used for developing crab cavity phase control specifications. We also benchmarked these simulations with theory.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA36
About •	Received ※ 02 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 02 September 2022
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WEPA48	Electromagnetic Design of a Compact RF Chopper for Heavy-Ion Beam Separation at FRIB	dipole, linac, simulation, MEBT	738
	A.C. Araujo Martinez, R.B. Agustsson, Y.C. Chen, S.V. Kutsaev RadiaBeam, Santa Monica, California, USA A.S. Plastun, X. Rao FRIB, East Lansing, Michigan, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, under SBIR grant DE- SC0020671. Rare isotope beams are produced at FRIB via fragmentation of a primary heavy ion beam in a thin target. The isotope beam of interest is contaminated with other fragments, which must be filtered out to ensure the delivery of rare isotopes with desired rates and purities. One of the stages of fragment separation uses an RF deflecting cavity to provide time-of-flight separation. However, to avoid neighboring bunches overlapping with each other and with the contaminants, it is necessary to increase the inter-bunch distance by a factor of four, corresponding to a 20.125 MHz rate. To solve this problem, we have developed an RF chopper system for the 500 keV/u primary heavy-ion beams. The system consists of a deflecting quarter wave resonator (QWR) cavity operating at 60.375 MHz, two dipole steering magnets, and a beam dump. In this paper, we present and discuss the optimization of the electromagnetic design of the QWR cavity and magnets, as well as some aspects, related to beam dynamics and conceptual engineering design.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA48
About •	Received ※ 02 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 08 September 2022
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WEPA49	Ferrite-Free Circulator for Precise Measurements of SRF Cavities with High Q-Factor	ISOL, SRF, resonance, experiment	742
	A.I. Pronikov, A.Yu. Smirnov RadiaBeam, Santa Monica, California, USA A.A. Krasnok Florida International University, Miami, Florida, USA S.N. Romanenko Zaporizhzhya National Technical University, Zaporizhzhya, Ukraine V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Funding: This work was supported by the US Department of Energy, Offices of High Energy and Nuclear Physics, awards DE-SC0020926 and DE-SC0022439. In this work, we suggest and investigate new magnetless circulators based on three resonators connected in a loop and parametrically modulated in time with mutual phase lag. The first design consists of three Fano resonators with a spectrally asymmetric response, in contrast to schemes based on the Lorentz resonators explored thus far. The second design includes three Fano-Lorentz resonators, i.e., it also possesses spatial asymmetry. We demonstrate that the asymmetric approach provides strong and reversible isolation for the practically feasible modulation amplitude and rate. The results of our work are promising for precise measurements of superconducting radio frequency cavities with high Q-factor.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA49
About •	Received ※ 04 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 13 September 2022
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WEPA52	Demonstration of Twice-Reduced Lorentz-Force Detuning in SRF Cavity by Copper Cold Spraying	SRF, site, niobium, accelerating-gradient	749
	R.A. Kostin, C.-J. Jing, A. Kanareykin Euclid TechLabs, Solon, Ohio, USA G. Ciovati JLab, Newport News, Virginia, USA
	Funding: The project is funded by DOE SBIR # DE-SC0019589 Superconducting RF (SRF) cavities usually are made from thin-walled high RRR Niobium and are susceptible to Lorentz Force Detuning (LFD) ’ cavity deformation phenomena by RF fields. In this paper, we present high gradient cryogenic results of an SRF cavity with two times reduced LFD achieved by copper cold spray reinforcement without sacrificing cavity flexibility for tuning. Finite-element model was developed first to find the best geometry for LFD reduction, which incorporated coupled RF, structural and thermal modules, and is also presented.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA52
About •	Received ※ 27 July 2022 — Revised ※ 03 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 16 August 2022
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WEPA55	Applications of Machine Automation with Robotics and Computer Vision in Cleanroom Assemblies	controls, SRF, operation, vacuum	756
	A. Liu, J.R. Callahan, E. Gomez, S.M. Milller, W. Si Euclid TechLabs, Solon, Ohio, USA
	Funding: This work is supported by the US DOE SBIR program under contract number DE-SC0021736. Modern linear particle accelerators use superconducting radio frequency (SRF) cavities for achieving extremely high-quality factors (Q) and higher beam stability. The assembly process of the system, although with a much more stringent cleanness requirement, is very similar to the ultrahigh vacuum (UHV) system operation procedure. Humans, who are conventionally the operators in this procedure, can only avoid contaminating the system by wearing proper sterile personal protection equipment to avoid direct skin contact with the systems, or dropping particulates. However, humans unavoidably make unintentional mistakes that can contaminate the environment: cross contamination of the coverall suits during wearing, slippage of masks or goggles, damaged gloves, and so forth. Besides, humans are limited when operating heavy weights, which may lead to incorrect procedures, or even worse, injury. In this paper, we present our recent work on a viable and cost-effective machine automation system composed of a robotic arm and a computer vision system for the assembly process in a cleanroom environment, for example for SRF string assemblies, and more.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA55
About •	Received ※ 30 July 2022 — Revised ※ 04 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 12 August 2022
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WEPA63	Extensions of the Complex (IQ) Baseband RF Cavity Model Including RF Source and Beam Interactions	controls, simulation, beam-loading, linac	767
	S.P. Jachim, B.J. Cook, J.R.S. Falconer Arizona State University, Tempe, USA
	Funding: This work was supported in part by NSF award #1935994. This paper extends prior work describing a complex envelope (i.e., baseband) dynamic model of excited accelerator RF cavities, including the effects of frequency detuning, beam loading, reflections, multiple drive ports, and parasitic modes. This model is presented here in closed-form transfer function and state-variable realizations, which may be more appropriate for analytic purposes. Several example simulations illustrate the detailed insight into RF system behavior afforded by this model.
DOI •	reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA63
About •	Received ※ 28 July 2022 — Revised ※ 08 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 15 August 2022
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WEPA69	The Impact on the Vertical Beam Dynamics Due to the Noise in a Horizontal Crab Crossing Scheme	emittance, feedback, electron, hadron	788

Paper

Title

Other Keywords

Page

MOYD3

EIC Transverse Emittance Growth Due to Crab Cavity RF Noise: Estimates and Mitigation

emittance, feedback, simulation, target

6

T. Mastoridis, P. Fuller, P. Mahvi, Y. Matsumura
CalPoly, San Luis Obispo, California, USA

Funding: This work is partially supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under Award Number DE-SC-0019287.
The Electron-Ion Collider (EIC) requires crab cavities to compensate for a 25 mrad crossing angle and achieve maximum luminosity. The crab cavity Radio Frequency (RF) system will inject low levels of noise to the crabbing field, generating transverse emittance growth and potentially limiting luminosity lifetime. In this work, we estimate the transverse emittance growth rate as a function of the Crab Cavity RF noise and quantify RF noise specifications for reasonable performance. Finally, we evaluate the possible mitigation of the RF noise induced emittance growth via a dedicated feedback system.

Slides MOYD3 [0.223 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOYD3

About •

Received ※ 28 July 2022 — Revised ※ 01 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 04 October 2022

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MOYD5

Tolerances of Crab Dispersion at the Interaction Point in the Hadron Storage Ring of the Electron-Ion Collider

proton, simulation, electron, dynamic-aperture

12

Y. Luo, J.S. Berg, M. Blaskiewicz, C. Montag, V. Ptitsyn, F.J. Willeke, D. Xu
BNL, Upton, New York, USA
Y. Hao
FRIB, East Lansing, Michigan, USA
V.S. Morozov
ORNL RAD, Oak Ridge, Tennessee, USA
J. Qiang
LBNL, Berkeley, California, USA
T. Satogata
JLab, Newport News, Virginia, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
The Electron Ion Collider (EIC) presently under construction at Brookhaven National Laboratory will collide polarized high energy electron beams with hadron beams with luminosity up to 10³⁴ cm^-2 s^-1 in the center mass energy range of 20 to 140 GeV. Due to the detector solenoid in the interaction region, the design horizontal crabbing angle will be coupled to the vertical plane if uncompensated. In this article, we estimate the tolerance of crab dispersion at the interaction point in the EIC Hadron Storage Ring (HSR). Both strong-strong and weak-strong simulations are used. We found that there is a tight tolerance of vertical crabbing angle at the interaction point in the HSR.

Slides MOYD5 [1.183 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOYD5

About •

Received ※ 01 August 2022 — Accepted ※ 04 August 2022 — Issue date ※ 15 August 2022

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MOYE3

Experiments on a Conduction Cooled Superconducting Radio Frequency Cavity with Field Emission Cathode

niobium, experiment, SRF, accelerating-gradient

16

Y. Ji, R. Dhuley, C.J. Edwards, J.C.T. Thangaraj
Fermilab, Batavia, Illinois, USA
V. Korampally, D. Mihalcea, O. Mohsen, P. Piot, I. Salehinia
Northern Illinois University, DeKalb, Illinois, USA

Funding: The project is supported by DOE HEP Accelerator Stewardship award to Fermilab and Northern Illinois University
To achieve Ampere-class electron beam accelerators the pulse delivery rate need to be much higher than the typical photo injector repetition rate of the order of a few kilohertz. We propose here an injector which can, in principle, generate electron bunches at the same rate as the operating RF frequency. A conduction-cooled superconducting radio frequency (SRF) cavity operating in the CW mode and housing a field emission element at its region of high axial electric field can be a viable method of generating high-repetition-rate electron bunches. In this paper, we report the development and experiments on a conduction-cooled Nb₃Sn cavity with a niobium rod intended as a field emitter support. The initial experiments demonstrate ~0.4 MV/m average accelerating gradient, which is equivalent of peak gradient of 3.2 MV/m. The measured RF cavity quality factor is 1.4 × 10⁸ slightly above our goal. The achieved field gradient is limited by the relatively low input RF power and by the poor coupling between the external power supply and the RF cavity. With ideal coupling the field gradient can be as high as 0.6 MV/m still below our goal of about 1 MV/m

Slides MOYE3 [1.444 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOYE3

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Received ※ 01 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 30 September 2022

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MOYE5

In Situ Plasma Processing of Superconducting Cavities at JLab

plasma, cryomodule, HOM, radiation

22

T. Powers, N.C. Brock, T.D. Ganey
JLab, Newport News, Virginia, USA

Jefferson Lab has an ongoing R&D program in plasma processing which is close to going into production processing in the CEBAF accelerator. Plasma processing is a common technique for removing hydrocarbons from surfaces, which increases the work function and reduces the secondary emission coefficient. Unlike helium processing which relies on ion bombardment of the field emitters, plasma processing uses free oxygen produced in the plasma to break down the hydrocarbons on the surface of the cavity. The initial focus of the effort was processing C100 cavities by injecting RF power into the HOM coupler ports. Results from processing cryomodule in the cryomodule test bunker as well as vertical test results will be presented. We plan to start processing cryomodules in the CEBAF tunnel within the next year. The goal will be to improve the operational gradients and the energy margin of the linacs. This work will describe the systems and methods used at JLAB for processing cavities using an argon oxygen gas mixture. Before and after plasma processing results will also be presented.

Slides MOYE5 [2.679 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOYE5

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Received ※ 01 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 01 October 2022

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MOZD6

Accelerator Physics Lessons from CBETA, the First Multi-Turn SRF ERL

linac, electron, SRF, photon

41

K.E. Deitrick
JLab, Newport News, Virginia, USA
G.H. Hoffstaetter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The Cornell-BNL ERL Test Accelerator (CBETA) has been designed, constructed, and commissioned in a collaboration between Cornell and BNL. It focuses on energy-saving measures in accelerators, including permanent magnets, energy recovery, and superconductors; it has thus been referred to as a green accelerator. CBETA has become the world’s first Energy Recovery Linac (ERL) that accelerates through multiple turns and then recovers the energy in SRF cavities though multiple decelerating turns. The energy is then available to accelerate more beam. It has also become the first accelerator that operates 7 beams in the same large-energy aperture Fixed Field Alternating-gradient (FFA) lattice. The FFA is constructed of permanent combined function magnets and transports energies of 42, 78, 114, and 150 MeV simultaneously. Accelerator physics lessons from the commissioning period will be described and applications of such an accelerator from hadron cooling to EUV lithography and from nuclear physics to a compact Compton source will be discussed.

Slides MOZD6 [3.207 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOZD6

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Received ※ 23 July 2022 — Revised ※ 27 July 2022 — Accepted ※ 03 August 2022 — Issue date ※ 06 August 2022

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MOZE4

Ceramic Enhanced Accelerator Structure Low Power Test and Designs of High Power and Beam Tests

electron, impedance, accelerating-gradient, simulation

49

H. Xu, M.R. Bradley, L.D. Duffy, M.A. Holloway, J. Upadhyay
LANL, Los Alamos, New Mexico, USA

Funding: Research was supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory, under project number 20210083ER.
A ceramic enhanced accelerator structure (CEAS) uses a concentric ceramic ring placed inside a metallic pillbox cavity to significantly increase the shunt impedance of the cavity. Single cell standing wave CEAS cavities are designed, built, and tested at low power at 5.1 GHz. The results indicate 40% increase in shunt impedance compared to that of a purely metallic pillbox cavity. A beam test setup has been designed to use a single cell CEAS cavity to modulate a 30-keV direct-current (DC) electron beam at an accelerating gradient of 1 to 2 MV/m to verify the beam acceleration capability of the CEAS concept and to study the potential charging effect on the ceramic component during the operation. Another single cell standing wave CEAS cavity has been designed for high power test at 5.7 GHz for the high accelerating gradient capability.

Slides MOZE4 [1.652 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOZE4

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Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 07 October 2022

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MOPA12

Commissioning of HOM Detectors in the First Cryomodule of the LCLS-II Linac

HOM, MMI, alignment, cryomodule

69

J.A. Diaz Cruz
UNM-ECE, Albuquerque, USA
B.T. Jacobson, N.R. Neveu, J.P. Sikora
SLAC, Menlo Park, California, USA

Long-range wakefields (LRWs) may cause emittance dilution effects. LWRs are especially unwanted at facilities with low emittance beams like the LCLS-II at SLAC. Dipolar higher-order modes (HOMs) are a set of LRWs that are excited by off-axis beams. Two 4-channel HOM detectors were built to measure the beam-induced HOM signals for TESLA-type superconducting RF (SRF) cavities; they were tested at the Fermilab Accelerator Science and Technology (FAST) facility and are now installed at SLAC. The HOM detectors were designed to investigate LRW effects on the beam and to help with beam alignment. This paper presents preliminary results of HOM measurements at the first cryomodule (CM01) of the LCLS-II linac and describes the relevant hardware and setup of the experiment.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA12

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Received ※ 09 August 2022 — Accepted ※ 20 August 2022 — Issue date ※ 31 August 2022

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MOPA21

Effect of Electropolishing on Nitrogen Doped and Undoped Niobium Surfaces

niobium, SRF, factory, superconducting-RF

93

V. Chouhan, F. Furuta, M. Martinello, T.J. Ring, G. Wu
Fermilab, Batavia, Illinois, USA

Cold electropolishing (EP) of a nitrogen-doped (N-doped) niobium (Nb) superconducting RF (SRF) cavity was found to improve its quality factor. In order to understand the effect of EP temperature on N-doped and undoped surfaces, a systematic EP study was conducted with 2/0 N-doped and heat-treated Nb samples in a beaker. The Nb samples were electropolished at different surface temperatures ranging from 0 to 42 C. The results showed that the doped surface was susceptible to the sample temperature during EP. EP resulted in the surface pitting on the doped samples where the number density of pits increased at a higher temperature. The surface results were compared with the surface of cutouts from a 9-cell cavity which was 2/0 N-doped and electropolished. This paper shows de-tailed surface features of the N-doped and undoped Nb surfaces electropolished at different temperatures.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA21

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Received ※ 20 July 2022 — Revised ※ 24 July 2022 — Accepted ※ 09 August 2022 — Issue date ※ 11 August 2022

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MOPA22

Study on Electropolishing Conditions for 650 MHz Niobium SRF Cavity

cathode, SRF, niobium, power-supply

97

V. Chouhan, D.J. Bice, F. Furuta, M. Martinello, M.K. Ng, H. Park, T.J. Ring, G. Wu
Fermilab, Batavia, Illinois, USA
B.M. Guilfoyle, M.P. Kelly, T. Reid
ANL, Lemont, Illinois, USA

The PIP II linear accelerator includes different types of niobium SRF cavities including 650 MHz elliptical low (0.61) and high (0.92) beta cavities. The elliptical cavity surface is processed with the electropolishing method. The elliptical cavities especially the low-beta 650 MHz cavities showed a rough equator surface after the EP was performed with the standard EP conditions. This work was focused to study the effect of different EP parameters, including cathode surface area, temperature and voltage, and optimize them to improve the cavity surface.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA22

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Received ※ 02 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 03 September 2022

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MOPA23

Tests of the Extended Range SRF Cavity Tuners for the LCLS-II HE Project

operation, cryomodule, SRF, vacuum

100

C. Contreras-Martinez, T.T. Arkan, A.T. Cravatta, B.D. Hartsell, J.A. Kaluzny, T.N. Khabiboulline, Y.M. Pischalnikov, S. Posen, G.V. Romanov, J.C. Yun
Fermilab, Batavia, Illinois, USA

The LCLS-II HE superconducting linac will produce multi-energy beams by supporting multiple undulator lines simultaneously. This could be achieved by using the cavity SRF tuner in the off-frequency detune mode. This off-frequency operation method was tested in the verification cryomodule (vCM) and CM 1 at Fermilab at 2 K. In both cases, the tuners achieved a frequency shift of -565±80 kHz. This study will discuss cavity frequency during each step as it is being assembled in the cryomodule string and finally when it is being tested at 2 K. Tracking the cavity frequency helped enable the tuners to reach this large frequency shift. The specific procedures of tuner setting during assembly will be presented.

Poster MOPA23 [0.654 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA23

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Received ※ 03 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 19 August 2022 — Issue date ※ 31 August 2022

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MOPA24

LCLS-II and HE Cryomodule Microphonics at CMTF at Fermilab

cryomodule, cryogenics, SRF, niobium

103

C. Contreras-Martinez, B.E. Chase, A.T. Cravatta, J.A. Einstein-Curtis, E.R. Harms, J.P. Holzbauer, J.N. Makara, S. Posen, R. Wang
Fermilab, Batavia, Illinois, USA
L.R. Doolittle
LBNL, Berkeley, California, USA

Microphonics causes the cavity to detune. This study discusses the microphonics of 16 cryomodules, 14 for LCLS-II and 2 for LCLS-II HE tested at CMTF. The peak detuning, as well as the RMS detuning for each cryomodule, will be discussed. For each cryomodule, the data was taken with enough soaking time to prevent any thermalization effects which can show up in the detuning. Each data capture taken was 30 minutes or longer and sampled at 1 kHz.

Poster MOPA24 [1.428 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA24

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Received ※ 03 August 2022 — Revised ※ 10 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 20 September 2022

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MOPA25

Simulated Lorentz Force Detuning Compensation with a Double Lever Tuner on a Dressed ILC/1.3 GHz Cavity at Room Temperature

controls, flattop, resonance, SRF

106

C. Contreras-Martinez, Y.M. Pischalnikov, J.C. Yun
Fermilab, Batavia, Illinois, USA

Pulsed SRF linacs with high accelerating gradients experience large frequency shifts caused by Lorentz force detuning (LFD). A piezoelectric actuator with a resonance control algorithm can maintain the cavity frequency at the nominal level thus reducing the RF power. This study uses a double lever tuner with a piezoelectric actuator for compensation and another piezoelectric actuator to simulate the effects of the Lorentz force pulse. A double lever tuner has an advantage by increasing the stiffness of the cavity-tuner system thus reducing the effects of LFD. The tests are conducted at room temperature and with a dressed 1.3 GHz 9-cell cavity.

Poster MOPA25 [0.931 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA25

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Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 13 August 2022

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MOPA27

Validation of the 650 MHz SRF Tuner on the Low and High Beta Cavities for PIP-II at 2 K

SRF, linac, operation, proton

109

C. Contreras-Martinez, S.K. Chandrasekaran, S. Cheban, G.V. Eremeev, I.V. Gonin, T.N. Khabiboulline, Y.M. Pischalnikov, O.V. Prokofiev, A.I. Sukhanov, J.C. Yun
Fermilab, Batavia, Illinois, USA

The PIP-II linac will include thirty-six B_G=0.61 and twenty-four B_G=0.92 650 MHz 5 cell elliptical SRF cavities. Each cavity will be equipped with a tuning system consisting of a double lever slow tuner for coarse frequency tuning and a piezoelectric actuator for fine frequency tuning. The same tuner will be used for both the B_G=0.61 and B_G=0.92 cavities. Results of testing the cavity-tuner system for the B_G=0.61 will be presented for the first time.

Poster MOPA27 [0.782 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA27

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Received ※ 03 August 2022 — Revised ※ 10 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 04 October 2022

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MOPA30

LCLS-II BCS Average Current Monitor

electron, hardware, MMI, LLRF

120

N.M. Ludlow, T.L. Allison, J.P. Sikora, J.J. Welch
SLAC, Menlo Park, California, USA

LCLS-II is a 4th generation light source at the SLAC National Accelerator Laboratory. LCLS-II will accelerate a 30 µA electron beam with a 1 MHz bunch rate with a new superconducting Continuous Waveform (CW) RF accelerator. The Average Current Monitor (ACM) is part of the Beam Containment System (BCS) for the LCLS-II accelerator. The Beam Containment System is a safety system that provides paths to safely shut the accelerator beam off under a variety of conditions. The Average Current Monitor is a beam diagnostic within the BCS that is used to verify that the accelerator is producing the appropriate current level and to limit beam power to allowed values to protect the machine and beam dumps. The average beam current is obtained by measuring the power level induced by the beam in a low Q cavity. By knowing the Q, the beta, and the coupling of the cavity, the instantaneous charge can be calculated, then integrating the instantaneous charge over one millisecond will yield the average current. This paper will discuss progress in the checkout process of the ACM LLRF hardware leading to LCLS-II commissioning.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA30

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Received ※ 16 July 2022 — Revised ※ 05 August 2022 — Accepted ※ 24 August 2022 — Issue date ※ 06 October 2022

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MOPA36

Optimization of Superconducting Linac for Proton Improvement Plan-II (PIP-II)

emittance, linac, quadrupole, solenoid

132

A. Pathak, E. Pozdeyev
Fermilab, Batavia, Illinois, USA

PIP-II is an essential upgrade of the Fermilab complex that will enable the world’s most intense high-energy beam of neutrinos for the international Deep Underground Neutrino Experiment at LBNF and support a broad physics program at Fermilab. Ultimately, the PIP-II superconducting linac will be capable of accelerating the H⁻ CW beam to 800 MeV with an average power of 1.6 MW. To operate the linac with such high power, beam losses and beam emittance growth must be tightly controlled. In this paper, we present the results of global optimization of the Linac options towards a robust and efficient physics design for the superconducting section of the PIP-II linac. We also investigate the impact of the nonlinear field of the dipole correctors on the beam quality and derive the requirement on the field quality using statistical analysis. Finally, we assess the need to correct the quadrupole focusing produced by Half Wave, and Single Spoke accelerating cavities. We assess the feasibility of controlling the beam coupling in the machine by changing the polarity of the field of Linac focusing solenoids

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA36

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Received ※ 02 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 01 October 2022

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MOPA38

Accelerated Lifetime Test of the SRF Dressed Cavity/Tuner System for the LCLS II HE Project

operation, SRF, vacuum, LabView

136

Y.M. Pischalnikov, T.T. Arkan, C. Contreras-Martinez, B.D. Hartsell, J.A. Kaluzny, Y.M. Orlov, R.V. Pilipenko, J.C. Yun
Fermilab, Batavia, Illinois, USA
W. Lahmadi
Wahid Lahmadi, Williston, USA

The off-frequency detune method is being considered for application in the LCLS-II-HE superconducting linac to produce multi-energy electron beams for supporting multiple undulator lines simultaneously. Design of the tuner has been changed to deliver roughly 3 times larger frequency tuning range. Working requirements for off-frequency operation (OFO) state that cavities be tuned at least twice a month. This specification requires the increase of the tuner longevity by 30 times compared with LCLS-II demands. Accelerated longevity tests of the LCLS-II HE dressed cavity with tuner were conducted at FNAL’s HTS. Detail analysis of wearing and impacts on performances of the tuner’s piezo and stepper motor actuators will be presented. Additionally, results of longevity testing of the dressed cavity bellow, when cooled down to 2 K and compressed by 2.6 mm for roughly 2000 cycles, will be presented.

Poster MOPA38 [3.026 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA38

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Received ※ 29 July 2022 — Revised ※ 06 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 11 August 2022

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MOPA59

Prediction of Gaseous Breakdown for Plasma Cleaning of RF Cavities

simulation, plasma, electron, electronics

174

S.A. Ahmed
Ansys, Inc., Canonsburg, USA

The quest for a high accelerating gradient in superconducting radio frequency cavity attracted scientists to adopt the plasma cleaning technology. Generating an efficient plasma inside a complex cavity structure for a desired frequency, gas types, and pressure for a given temperature is a challenge. The onset of discharge can be obtained from the well-known Paschen curve. Setting up an experiment is expensive and time-consuming, which may lead to a significant delay in the project. A high-fidelity computer simulation, modeling an arbitrary geometry and tracking the Paschen curve in a complex electromagnetic environment is therefore necessary. Ansys HFSS through its Finite Element Mesh (FEM) for the full-wave EM simulations combined with the electron impact ionization of gases enables the successful prediction of plasma breakdown for an arbitrary configuration for a wide frequency band and variety of gases. A comprehensive study will be demonstrated at the conference.
The author like to thank Robert Chao for the valuable discussions and his efforts in developing this capability in the Ansys Electronics Desktop.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA59

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Received ※ 01 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 19 August 2022

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MOPA60

HFSS Enables Multipaction Analysis of High Power RF/Microwave Components

multipactoring, electron, simulation, vacuum

176

S.A. Ahmed
Ansys, Inc., Canonsburg, USA

The radiofrequency (RF) components in particle accelerators operated under a vacuum and driven by high RF power may be prone to electron multipaction ’ an RF triggered electron resonance phenomenon causing malfunction or complete breakdown. Therefore, exploring the design challenges of vacuum RF windows, cavities, and other devices for the electron multipaction becomes necessary. Setting up an experiment to mitigate the failure of RF devices is expensive and time-consuming, which may cause a significant delay in the project. Therefore, a high-fidelity computer simulation modeling the arbitrary geometry and tracking the particles (electrons) in a complex electromagnetic environment is desirable. Ansys HFSS through Finite Element Mesh (FEM) for the full-wave RF simulation combined with the particle-in-cell (PIC) technique for tracking particles in EM fields; enables the engineers/physicist successful prediction of system failure against the electron multipaction. This paper will demonstrate the workflow of the HFSS multipaction analysis.
The author like to thank Robert Chao for the valuable discussions and his efforts in developing this capability in the Ansys Electronics Desktop.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA60

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Received ※ 03 August 2022 — Revised ※ 13 August 2022 — Accepted ※ 26 August 2022 — Issue date ※ 06 October 2022

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MOPA67

Examining the Effects of Oxygen Doping on SRF Cavity Performance

SRF, niobium, ECR, radio-frequency

196

H. Hu, Y.K. Kim
University of Chicago, Chicago, Illinois, USA
D. Bafia
Fermilab, Batavia, Illinois, USA

Superconducting radiofrequency (SRF) cavities are resonators with extremely low surface resistance that enable accelerating cavities to have extremely high quality factors (Q₀). High (Q₀) decreases the capital required to keep accelerators cold by reducing power loss. The performance of SRF cavities is largely governed by the surface composition of the first 100 nm of the cavity surface. Impurities such as oxygen and nitrogen have been observed to yield high Q₀, but their precise roles are still being studied. Here, we compare the performance of cavities doped with nitrogen and oxygen in terms of fundamental material properties to understand how these impurities affect performance. This enables us to have further insight into the underlying mechanisms that enable these surface treatments to yield high Q₀ performance.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA67

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Received ※ 02 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 03 October 2022

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MOPA72

Preliminary Tests and Beam Dynamics Simulations of a Straight-Merger Beamline

dipole, experiment, simulation, electron

206

A.A. Al Marzouk, P. Piot, T. Xu
Northern Illinois University, DeKalb, Illinois, USA
S.V. Benson, K.E. Deitrick, J. Guo, A. Hutton, G.-T. Park, S. Wang
JLab, Newport News, Virginia, USA
D.S. Doran, G. Ha, P. Piot, J.G. Power, C. Whiteford, E.E. Wisniewski
ANL, Lemont, Illinois, USA
C.E. Mitchell, J. Qiang, R.D. Ryne
LBNL, Berkeley, California, USA

Funding: NSF award PHY-1549132 to Cornell University and NIU, U.S. DOE contract DE-AC02-06CH11357 with ANL and DE-AC05-06OR23177 with JLAB.
Beamlines capable of merging beams with different energies are critical to many applications related to advanced accelerator concepts and energy-recovery linacs (ERLs). In an ERL, a low-energy "fresh" bright bunch is generally injected into a superconducting linac for acceleration using the fields established by a decelerated "spent" beam traveling on the same axis. A straight-merger system composed of a selecting cavity with a superimposed dipole magnet was proposed and recently test at AWA. This paper reports on the experimental results obtained so far along with detailed beam dynamics investigations of the merger concept and its ability to conserve the beam brightness associated with the fresh bunch.

Poster MOPA72 [1.659 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA72

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Received ※ 11 August 2022 — Accepted ※ 13 August 2022 — Issue date ※ 02 October 2022

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MOPA83

Automation of Superconducting Cavity and Superconducting Magnet Operation for FRIB

operation, linac, solenoid, cryomodule

239

W. Chang, Y. Choi, X.-J. Du, W. Hartung, S.H. Kim, T. Konomi, S.R. Kunjir, H. Nguyen, J.T. Popielarski, K. Saito, T. Xu, S. Zhao
FRIB, East Lansing, Michigan, USA

The superconducting (SC) driver linac for the Facility for Rare Isotope Beams (FRIB) is a heavy-ion accelerator that accelerate ions to 200 MeV per nucleon. The linac has 46 cryomodules that contain 324 SC cavities and 69 SC solenoid packages. For linac operation with high availability and high reliability, automation is essential for such tasks as fast device turn-on/off, fast recovery from trips, and real-time monitoring of operational performance. We have implemented several automation algorithms, including one-button turn-on/off of SC cavities and SC magnets; automated degaussing of SC solenoids; mitigation of field emission-induced multipacting during recovery from cavity trips; and real-time monitoring of the cavity field level calibration. The design, development, and operating experience with automation will be presented.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA83

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Received ※ 02 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 26 August 2022

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MOPA84

Superconducting Cavity Commissioning for the FRIB Linac

MMI, cryomodule, controls, linac

242

W. Chang, W. Hartung, S.H. Kim, T. Konomi, S.R. Kunjir, J.T. Popielarski, K. Saito, T. Xu, S. Zhao
FRIB, East Lansing, Michigan, USA

The superconducting driver linac for the Facility for Rare Isotope Beams (FRIB) is a heavy ion accelerator that has 46 cryomodules with 324 superconducting (SC) cavities that accelerate ions to 200 MeV per nucleon. Linac commissioning was done in multiple phases, in parallel with technical installation. Ion beam have now been accelerated to the design energy through the full linac; rare isotopes were first produced in December 2021; and the first user experiment was completed in May 2022. All cryomodules were successfully commissioned. Cryomodule commissioning included establishing the desired cavity fields, measuring field emission X-rays, optimizing the tuner control loops, measuring the cavity dynamic heat load, and confirming the low-level RF control (amplitude and phase stability). Results on cryomodule commissioning and cryomodule performance will be presented.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA84

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Received ※ 13 July 2022 — Revised ※ 02 August 2022 — Accepted ※ 13 August 2022 — Issue date ※ 05 September 2022

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MOPA85

Design of a 185.7 MHz Superconducting RF Photoinjector Quarter-Wave Resonator for the LCLS-II-HE Low Emittance Injector

SRF, gun, cathode, electron

245

S.H. Kim, W. Hartung, T. Konomi, S.J. Miller, M.S. Patil, J.T. Popielarski, K. Saito, T. Xu, T. Xu
FRIB, East Lansing, Michigan, USA
C. Adolphsen, L. Ge, F. Ji, J.W. Lewellen, L. Xiao
SLAC, Menlo Park, California, USA
M.P. Kelly, T.B. Petersen, P. Piot
ANL, Lemont, Illinois, USA
P. Piot
Northern Illinois University, DeKalb, Illinois, USA

Funding: Work supported by the U.S. Department of Energy Contract DE-AC02-76SF00515.
A 185.7 MHz superconducting quarter-wave resonator (QWR) was designed for the low emittance injector of the Linac Coherent Light Source high energy upgrade (LCLS-II-HE). The cavity was designed to minimize the risk of cathode efficiency degradation due to multipacting or field emission and to operate with a high RF electric field at the cathode for low electron-beam emittance. Cavity design features include: (1) shaping of the cavity wall to reduce the strength of the low-field coaxial multipacting barrier; (2) four ports for electropolishing and high-pressure water rinsing; and (3) a fundamental power coupler (FPC) port located away from the accelerating gap. The design is oriented toward minimizing the risk of particulate contamination and avoid harmful dipole components in the RF field. The ANL 162 MHz FPC design for PIP-II is being adapted for the gun cavity. We will present the RF design of the cavity integrated with the FPC.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA85

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Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 30 August 2022

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MOPA86

Conditioning of Low-Field Multipacting Barriers in Superconducting Quarter-Wave Resonators

coupling, multipactoring, cryomodule, electron

249

S.H. Kim, W. Chang, W. Hartung, J.T. Popielarski, T. Xu
FRIB, East Lansing, Michigan, USA

Funding: This is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661, the State of Michigan and Michigan State University.
Multipacting (MP) barriers are typically observed at very low RF amplitude, at a field 2 to 3 orders of magnitude below the operating gradient, in low-frequency (<~100 MHz), quarter-wave resonators (QWRs). Such barriers may be troublesome, as RF conditioning with a fundamental power coupler (FPC) of typical coupling strength (external Q = 10⁶ to 10⁷) is generally difficult. For the FRIB \beta = 0.085 QWRs (80.5 MHz), the low barrier is observed at an accelerating gradient (E_acc) of ~10 kV/m; the operating E_acc is 5.6 MV/m. Theoretical and simulation studies suggested that the conditioning is difficult due to the relatively low RF power dissipated into multipacting rather than being a problem of the low barrier being stronger than other barriers. We developed a single-stub coaxial FPC matching element for external adjustment of the external Q by one order of magnitude. The matching element provided a significant reduction in the time to condition the low barrier. We will present theoretical and simulation studies of the low MP barrier and experimental results on MP conditioning with the single-stub FPC matching element.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA86

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Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 21 August 2022

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MOPA87

Design of the Cathode Stalk for the LCLS-II-HE Low Emittance Injector

cathode, gun, SRF, ISOL

253

T. Konomi, W. Hartung, S.H. Kim, S.J. Miller, D.G. Morris, J.T. Popielarski, K. Saito, A. Taylor, T. Xu
FRIB, East Lansing, Michigan, USA
C. Adolphsen, J.W. Lewellen
SLAC, Menlo Park, California, USA
S. Gatzmaga, P. Murcek, R. Xiang
HZDR, Dresden, Germany
M.P. Kelly, T.B. Petersen
ANL, Lemont, Illinois, USA

Superconducting radio-frequency (SRF) electron guns are attractive for delivery of beams at a high bunch repetition rate with a high accelerating field. An SRF gun is the most suitable injector for the high-energy upgrade of the Linac Coherent Light Source (LCLS-II-HE), which will produce high-energy X-rays at high repetition rate. An SRF gun is being developed for LCLS-II-HE as a collaborative effort by FRIB, HZDR, ANL, and SLAC. The cavity operating frequency is 185.7 MHz, and the target accelerating field at the photocathode is 30 MV/m. The photocathode is replaceable. The cathode is held by a fixture (’cathode stalk’) that is designed for thermal isolation and particle-free cathode exchange. The stalk must allow for precise alignment of the cathode position, cryogenic or room-temperature cathode operating temperature, and DC bias to inhibit multipacting. We are planning a test of the stalk to confirm that the design meets the requirements for RF power dissipation and biasing. In this presentation, we will describe the cathode stalk design and RF/DC stalk test plan.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA87

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Received ※ 04 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 18 August 2022 — Issue date ※ 11 September 2022

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MOPA88

FRIB and UEM LLRF Controller Upgrade

controls, LLRF, FPGA, operation

256

S.R. Kunjir, E. Bernal, D.G. Morris, S. Zhao
FRIB, East Lansing, Michigan, USA
C.-Y. Ruan
MSU, East Lansing, Michigan, USA

Funding: Supported by the U.S. DOE Office of Science under Cooperative Agreement DE-SC0000661, the State of Michigan, Michigan State University and U.S. National Science Foundation grant DMR-1625181.
The Facility for Rare Isotope Beams (FRIB) is developing a 644 MHz superconducting (SC) cavity for a future upgrade project. The current low level radio frequency (LLRF) controller at FRIB is not able to operate at 644 MHz. The Ultrafast Electron Microscope (UEM) laboratory within the Department of Physics at Michigan State University designed an LLRF controller based on analog RF components to operate a 1.013 GHz room temperature (RT) cavity. With requirements for improved stability, performance and user controls there was a need to upgrade the analog LLRF controller. The FRIB radio frequency (RF) group designed, developed and fabricated a new digital LLRF controller, with high-speed serial interface between system on chip field programmable gate array and fast data converters and capable of high frequency direct sampling, to meet the requirements of 644 MHz SC cavity and 1.013 GHz UEM RT cavity. This paper gives an overview of the upgraded digital LLRF controller, its features, improvements and preliminary test results.

Poster MOPA88 [2.818 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA88

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Received ※ 01 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 04 August 2022 — Issue date ※ 16 August 2022

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MOPA91

Plasma Processing of Superconducting Quarter-Wave Resonators Using a Higher-Order Mode

plasma, SRF, cryomodule, HOM

267

W. Hartung, W. Chang, K. Elliott, S.H. Kim, T. Konomi, J.T. Popielarski, K. Saito, T. Xu
FRIB, East Lansing, Michigan, USA

The Facility for Rare Isotope Beams (FRIB) is a superconducting ion linac with acceleration provided by 104 quarter-wave resonators (QWRs) and 220 half-wave resonators (HWRs); FRIB user operations began in May 2022. Plasma cleaning is being developed as a method to mitigate possible future degradation of QWR or HWR performance: in-situ plasma cleaning represents an alternative to removal and disassembly of cryomodules for refurbishment of each cavity via repeat etching and rinsing. Initial measurements were done on a QWR and an HWR with room-temperature-matched input couplers to drive the plasma via the fundamental mode. Subsequent plasma cleaning tests were done on two additional FRIB QWRs using the fundamental power coupler (FPC) to drive the plasma. When using the FPC, a higher-order mode (HOM) at 5 times the accelerating mode frequency was used to drive the plasma. Use of the HOM allowed for less mismatch at the FPC and hence lower field in the coupler relative to the cavity. A neon-oxygen gas mixture was used for plasma generation. Before and after cold tests showed a significant reduction in field emission X-rays after plasma cleaning. Results will be presented.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA91

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Received ※ 12 August 2022 — Revised ※ 16 August 2022 — Accepted ※ 25 August 2022 — Issue date ※ 16 September 2022

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TUXD6

Dual Radiofrequency Cavity Based Monochromatization for High Resolution Electron Energy Loss Spectroscopy

electron, cathode, simulation, space-charge

278

A.V. Kulkarni, P.E. Denham, A. Kogar, P. Musumeci
UCLA, Los Angeles, USA

Reducing the energy spread of electron beams can enable breakthrough advances in electron energy loss spectroscopic investigations of solid state samples where characteristic excitations typically have energy scales on the order of meV. In conventional electron sources the energy spread is limited by the emission process and typically on the order of a fraction of an eV. State-of-the-art energy resolution can only be achieved after significant losses in the monochromatization process. Here we propose to take advantage of photoemission from ultrashort laser pulses (~40 fs) so that after a longitudinal phase space manipulation that trades pulse duration for energy spread, the energy spread can be reduced by more than one order of magnitude. The scheme uses two RF cavities to accomplish this goal and can be implemented on a relatively short (~ 1m) beamline. Analytical predictions and results of 3D self consistent beam dynamics simulations are presented to support the findings.

Slides TUXD6 [1.461 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUXD6

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Received ※ 03 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 18 August 2022

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TUPA11

Magnet System for a Compact Microtron Source

microtron, electron, extraction, injection

363

S.A. Kahn, R.J. Abrams, M.A. Cummings, R.P. Johnson, G.M. Kazakevich
Muons, Inc, Illinois, USA

Funding: Work supported in part by U.S. D.O.E. SBIR grant DE-SC0013795.
A microtron can be an effective intense electron source. It can use less RF power than a linac to produce a similar energy because the beam will pass through the RF cavity several times. To produce a high-quality low-emittance beam with a microtron requires a magnetic system with a field uniformity $δ B/B<0.001. Field quality for a compact microtron with fewer turns is more difficult to achieve. In this study we describe the magnet for a compact S-band microtron that will achieve the necessary field requirements. The shaping of the magnet poles and shimming of the magnet iron at the outer extent of the poles will be employed to provide field uniformity. The extraction of the beam will be discussed.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA11

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Received ※ 04 August 2022 — Revised ※ 14 August 2022 — Accepted ※ 06 September 2022 — Issue date ※ 08 October 2022

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TUPA13

Affordable, Efficient Injection-Locked Magnetrons for Superconducting Cavities

injection, electron, controls, GUI

366

M. Popovic, M.A. Cummings, R.P. Johnson, S.A. Kahn, R.R. Lentz, M.L. Neubauer, T. Wynn
Muons, Inc, Illinois, USA
T. Blassick, J.K. Wessel
Richardson Electronics Ltd, Lafox, Illinois, USA

Funding: DE-SC0022586.
Existing magnetrons that are typically used to study methods of control or lifetime improvements for SRF accelerators are built for much different applications such kitchen microwave ovens (1kW, 2.45 GHz) or industrial heating (100 kW, 915 MHz). In this project, Muons, Inc. will work with an industrial partner to develop fast and flexible manufacturing techniques to allow many ideas to be tested for construction variations that enable new phase and amplitude injection locking control methods, longer lifetime, and inexpensive refurbishing resulting in the lowest possible life-cycle costs. In Phase II magnetron sources will be tested on SRF cavities to accelerate an electron beam at JLab. A magnetron operating at 650 MHz will be constructed and tested with our novel patented subcritical voltage operation methods to drive an SRF cavity. The choice of 650 MHz is an optimal frequency for magnetron efficiency. The critical areas of magnetron manufacturing and design affecting life-cycle costs that will be modeled for improvement include: Q_ext, filaments, magnetic field, vane design, and novel control of outgassing.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA13

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Received ※ 05 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 23 August 2022

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TUPA15

Development of a CVD System for Next-Generation SRF Cavities

controls, SRF, GUI, vacuum

372

G. Gaitan, P. Bishop, A.T. Holic, G. Kulina, J. Sears, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
M. Liepe
Cornell University, Ithaca, New York, USA
B.W. Wendland
University of Minnesota, Minnesota, USA

Funding: This research is funded by the National Science Foundation under Grant No. PHY-1549132, the Center for Bright Beams.
Next-generation, thin-film surfaces employing Nb₃Sn, NbN, NbTiN, and other compound superconductors are destined to allow reaching superior RF performance levels in SRF cavities. Optimized, advanced deposition processes are required to enable high-quality films of such materials on large and complex-shaped cavities. For this purpose, Cornell University is developing a remote plasma-enhanced chemical vapor deposition (CVD) system that facilitates coating on complicated geometries with a high deposition rate. This system is based on a high-temperature tube furnace with a clean vacuum and furnace loading system. The use of plasma alongside reacting precursors will significantly reduce the required processing temperature and promote precursor decomposition. The system can also be used for annealing cavities after the CVD process to improve the surface layer. The chlorine precursors have the potential to be corrosive to the equipment and pose specific safety concerns. A MATLAB GUI has been developed to control and monitor the CVD system at Cornell.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA15

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Received ※ 14 July 2022 — Revised ※ 08 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 22 August 2022

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TUPA27

Longitudinal Feedback Dynamics in Storage Rings with Small Synchrotron Tunes

feedback, HOM, simulation, synchrotron

405

R.R. Lindberg
ANL, Lemont, Illinois, USA

Funding: This work was supported by U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357.
We analyze the dynamics of multibunch longitudinal instabilities including bunch-by-bunch feedback under the assumption that the synchrotron tune is small. We find that increasing the feedback response does not always guarantee stability, even in the ideal case with no noise. As an example, we show that if the growth rate of a cavity-driven mode is of the order of the synchrotron frequency, then there are parameter regions for which the instability cannot be controlled by feedback irrespective of its gain. We verify these calculations with tracking simulations relevant to the APS-U, and find that the dynamics do not depend upon whether the longitudinal feedback relies on phase-sensing or energy-sensing technology. Hence, this choice should be dictated by measurement accuracy and noise considerations.

Poster TUPA27 [1.180 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA27

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Received ※ 26 July 2022 — Revised ※ 05 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 26 August 2022

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TUPA43

Novel RF Phase Detector for Accelerator Applications

detector, controls, LLRF, feedback

446

J.M. Potter
JP Accelerator Works, Los Alamos, New Mexico, USA

A novel phase detector has been developed that is suitable for use in an rf phase locked loop for locking an rf source to an rf accelerator structure or phase locking the accelerator structure to a fixed or adjustable frequency rf source. It is also useful for fast phase feedback to control the phase of an accelerator rf field. The principle is applicable to a wide range of frequencies and amplitudes. The phase is uniquely and unambiguously determined over 360°, eliminating the need for external phase shifters or phase references. The operation of this phase detector is described in detail. An application is described that uses a DDS-based LLRF source as the rf input to a high-power rf system.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA43

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Received ※ 02 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 06 October 2022

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TUPA57

Electromagnetic and Beam Dynamics Modeling of the LANSCE Coupled-Cavity Linac

linac, simulation, emittance, quadrupole

472

S.S. Kurennoy, Y.K. Batygin, D.V. Gorelov
LANL, Los Alamos, New Mexico, USA

The 800-MeV proton linac at LANSCE consists of a drift-tube linac, which brings the beam to 100 MeV, followed by a coupled-cavity linac (CCL) consisting of 44 modules. Each CCL module contains multiple tanks, and it is fed by a single 805-MHz klystron. CCL tanks are multi-cell blocks of identical re-entrant side-coupled cavities, which are followed by drifts with magnetic quadrupole doublets. Bridge couplers - special cavities displaced from the beam axis - electromagnetically couple CCL tanks over such drifts. We have developed 3D CST models of CCL tanks. Their electromagnetic analysis is performed using MicroWave Studio. Beam dynamics is modeled with Particle Studio for bunch trains with realistic beam distributions using the CST calculated RF fields and quadrupole magnetic fields to determine the output beam parameters. Beam dynamics results are crosschecked with other multi-particle codes.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA57

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Received ※ 15 July 2022 — Revised ※ 01 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 19 August 2022

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TUPA58

Iterative Tuning of the Beam Feedforward Controller for LANSCE LINAC Digital Low Level RF Control System

controls, beam-loading, LLRF, neutron

475

S. Kwon, A.T. Archuleta, L.J. Castellano, M.S. Prokop, C. Rose, P.A. Torrez, P. Van Rooy
LANL, Los Alamos, New Mexico, USA

Funding: USDOE
This paper addresses an iterative particle beam phase and amplitude feedforward controller tuning method based on the gradient search approach. The method does not need an a priori plant model as it only needs data collected in previous experimental runs. The controller is implemented on a field programmable gate array (FPGA) equipped with a real-time operating system and a network connection. Data from each RF pulse is collected and sent via the network to the FPGA for processing. The controller tuning is performed between the RF pulses. Once the tuning is performed, the controller parameters are downloaded to the controller in the FPGA and new controller parameters are applied at the upcoming RF pulse

Poster TUPA58 [0.998 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA58

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Received ※ 01 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 07 September 2022

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TUPA59

RF System Upgrade for Low Energy DTL Cavity at LANSCE

controls, DTL, LLRF, MMI

478

J.T.M. Lyles, R.E. Bratton, T.W. Hall, M. Sanchez Barrueta
LANL, Los Alamos, New Mexico, USA

Funding: Work supported by the United States Department of Energy, National Nuclear Security Agency, under contract 89233218CNA000001.
The Los Alamos Neutron Science Center (LANSCE) 100-MeV Drift Tube Linac (DTL) uses four accelerating cavities. In May of 2021, a new RF amplifier system was commissioned to drive the first 4-MeV cavity. It had been powered for 30 years with a triode vacuum tube RF amplifier driven by a tetrode, along with four more vacuum tubes for anode high-voltage modulation. The new amplifier system uses one tetrode amplifier driven by a 20-kW solid state amplifier (SSA) to generate 400 kWp at 201.25 MHz. The tetrode amplifier is protected for reflected power from the DTL by a coaxial circulator. The new installation includes cRio controls and a fast protection and monitoring system capable of reacting to faults within 10 µs. A new digital low-level RF (LLRF) system has been installed that integrates I/Q signal processing, PI feedback, and feedforward controls for beam loading compensation. Issues with LLRF stability were initially encountered due to interaction from thermal-related RF phase changes. After these issues were solved, the final outcome has been a reliable new RF system to complete the overall upgrade of the LANSCE DTL RF power plant.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA59

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Received ※ 03 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 12 August 2022

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TUPA69

Improving Cavity Phase Measurements at Los Alamos Neutron Science Center

GUI, LLRF, controls, neutron

493

P. Van Rooy, A.T. Archuleta, L.J. Castellano, S. Kwon, M.S. Prokop, P.A. Torrez
LANL, Los Alamos, New Mexico, USA

Control stability of the phase and amplitude in the cavity is a significant contributor to beam performance. The ability to measure phase and amplitude of pulsed RF systems at accuracies of ± 0.1 degrees and ± 0.1 percent required for our systems is difficult, and custom-designed circuitry is required. The digital low-level RF upgrade at the Los Alamos Neutron Science Center is continuing to progress with improved cavity phase measurements. The previous generation of the cavity phase and amplitude measurement system has a phase ambiguity, which requires repeated calibrations to ascertain the correct phase direction. The new phase measurement system removes the ambiguity and the need for field calibration while improving the range and precision of the cavity phase measurements. In addition, the new digital low-level RF systems is designed to upgrade the legacy system without significant mechanical, electrical, or cabling changes. Performance data for the new phase measurement system is presented.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA69

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Received ※ 02 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 21 August 2022 — Issue date ※ 08 September 2022

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TUPA73

Design and Low Power Test of an Electron Bunching Enhancer Using Electrostatic Potential Depression

electron, simulation, gun, experiment

499

H. Xu, B.E. Carlsten, Q.R. Marksteiner
LANL, Los Alamos, New Mexico, USA
B.L. Beaudoin, T.W. Koeth, A. Ting
UMD, College Park, Maryland, USA

Funding: This project was supported by the U.S. Department of Energy Office of Science through the Accelerator Stewardship Program.
We present our experimental design and low power test results of a structure for the proof-of-principle demonstration of fast increase of the first harmonic current content in a bunched electron beam, using the technique of electrostatic potential depression (EPD). A primarily bunched electron beam from an inductive output tube (IOT) at 710 MHz first enters an idler cavity, where the longitudinal slope of the beam energy distribution is reversed. The beam then transits through an EPD section implemented by a short beam pipe with a negative high voltage bias, inside which the rate of increase of the first harmonic current is significantly enhanced. An output cavity measures the harmonic current developed inside the beam downstream of the EPD section. Low power test results of the idler and the output cavities agree with the theoretical design.

Poster TUPA73 [1.307 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA73

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Received ※ 29 July 2022 — Accepted ※ 03 August 2022 — Issue date ※ 09 August 2022

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TUPA75

High Gradient Testing Results of the Benchmark a/λ=0.105 Cavity at CERF-NM

GUI, klystron, coupling, MMI

505

M.R.A. Zuboraj, D.V. Gorelov, T.W. Hall, M.E. Middendorf, D. Rai, E.I. Simakov, T. Tajima
LANL, Los Alamos, New Mexico, USA

Funding: This work was supported by Los Alamos National Laboratory’s Laboratory Directed Research and Development (LDRD) Program.
This presentation will report initial results of high gradient testing of two C-band accelerating cavities fabricated at Los Alamos National Laboratory (LANL). At LANL, we commissioned a C-band Engineering Research Facility of New Mexico (CERF-NM) which has unique capability of conditioning and testing accelerating cavities for operation at surface electric fields at the excess of 300 MV/m, powered by a 50 MW, 5.712 GHz Canon klystron. Recently, we fabricated and tested two benchmark copper cavities at CERF-NM. These cavities establish a benchmark for high gradient performance at C-band and the same geometry will be used to provide direct comparison between high gradient performance of cavities fabricated of different alloys and by different fabrication methods. The cavities consist of three cells with one high gradient central cell and two coupling cells on the sides. The ratio of the radius of the coupling iris to the wavelength is a/λ=0.105. This poster will report high gradient test results such as breakdown rates as function of peak surface electric and magnetic fields and pulse heating.

Poster TUPA75 [0.890 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA75

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Received ※ 05 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 01 October 2022

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TUPA77

X-Band Harmonic Longitudinal Phase Space Linearization at the PEGASUS Photoinjector

linac, electron, gun, laser

508

P.E. Denham, P. Musumeci, A. Ody
UCLA, Los Angeles, USA

Due to the finite bunch length, photoemitted electron beams sample RF-nonlinearities that lead to energy-time correlations along the bunch temporal profile. This is an important effect for all applications where the projected energy spread is important. In particular, for time-resolved single shot electron microscopy, it is critical to keep the beam energy spread below 1·10^-4 to avoid chromatic aberrations in the lenses. Higher harmonic RF cavities can be used to compensate for the RF-induced longitudinal phase space nonlinearities. Start-to-end simulations suggest that this type of compensation can reduce energy spread to the 1·10^-5 level. This work is an experimental study of x-band harmonic linearization of a beam longitudinal phase space at the PEGASUS facility, including developing high-resolution spectrometer diagnostics to verify the scheme.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA77

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Received ※ 25 July 2022 — Revised ※ 04 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 10 August 2022

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TUPA80

Cyborg Beamline Development Updates

gun, cathode, cryogenics, simulation

512

G.E. Lawler, A. Fukasawa, N. Majernik, J.R. Parsons, J.B. Rosenzweig, Y. Sakai
UCLA, Los Angeles, California, USA
F. Bosco
Sapienza University of Rome, Rome, Italy
Z. Li, S.G. Tantawi
SLAC, Menlo Park, California, USA
B. Spataro
LNF-INFN, Frascati, Italy

Funding: This work was supported by the Center for Bright Beams, National Science Foundation Grant No. PHY-1549132 and DOE Contract DE-SC0020409.
Xray free electron laser (XFEL) facilities in their current form are large, costly to maintain, and inaccessible due to their minimal supply and high demand. It is then advantageous to consider miniaturizing XFELs through a variety of means. We hope to increase beam brightness from the photoinjector via high gradient operation (>120 MV/m) and cryogenic temperature operation at the cathode (<77K). To this end we have designed and fabricated our new CrYogenic Brightness-Optimized Radiofrequency Gun (CYBGORG). The photogun is 0.5 cell so much less complicated than our eventual 1.6 cell photoinjector. It will serve as a prototype and test bed for cathode studies in a new cryogenic and very high gradient regime. We present here the fabricated structure, progress towards commissioning, and beamline simulations.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA80

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Received ※ 02 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 09 October 2022

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TUPA81

Design of a High-Power RF Breakdown Test for a Cryocooled C-Band Copper Structure

cryogenics, GUI, distributed, electron

516

G.E. Lawler, A. Fukasawa, J.R. Parsons, J.B. Rosenzweig
UCLA, Los Angeles, California, USA
Z. Li, S.G. Tantawi
SLAC, Menlo Park, California, USA
A. Mostacci
Sapienza University of Rome, Rome, Italy
E.I. Simakov, T. Tajima
LANL, Los Alamos, New Mexico, USA
B. Spataro
LNF-INFN, Frascati, Italy

Funding: This work was supported by the DOE Contract DE-SC0020409.
High-gradient RF structures capable of maintaining gradients in excess of 250 MV/m are critical in several concepts for future electron accelerators. Concepts such as the ultra-compact free electron laser (UC-XFEL) and the Cool Copper Collider (C3) plan to obtain these gradients through the cryogenic operation (<77K) of normal conducting copper cavities. Breakdown rates, the most significant gradient limitation, are significantly reduced at these low temperatures, but the precise physics is complex and involves many interacting effects. High-power RF breakdown measurements at cryogenic temperatures are needed at the less explored C-band frequency (5.712 GHz), which is of great interest for the aforementioned concepts. On behalf of a large collaboration of UCLA, SLAC, LANL, and INFN, the first C-band cryogenic breakdown measurements will be made using a LANL RF test infrastructure. The 2-cell geometry designed for testing will be modifications of the distributed coupled reentrant design used to efficiently power the cells while staying below the limiting values of peak surface electric and magnetic fields.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA81

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Received ※ 29 July 2022 — Accepted ※ 02 August 2022 — Issue date ※ 08 August 2022

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WEYE2

Upgrade of the FRIB ReAccelerator

cryomodule, experiment, MMI, ion-source

572

A.C.C. Villari, B. Arend, G. Bollen, D.B. Crisp, K.D. Davidson, K. Fukushima, A.I. Henriques, K. Holland, S.H. Kim, A. Lapierre, Y. Liu, T. Maruta, D.G. Morris, S. Nash, P.N. Ostroumov, A.S. Plastun, J. Priller, S. Schwarz, B.M. Sherrill, M. Steiner, C. Sumithrarachchi, R. Walker, T. Zhang, Q. Zhao
FRIB, East Lansing, Michigan, USA

Funding: Work supported by the NSF under grant PHY15-65546 and DOE-SC under award number DE-SC0000661
The reaccelerator facility at FRIB was upgraded to provide new science opportunities. The upgrade included a new ion source to produce stable and long livied rare isotopes in a batch mode, a new room-temperature rebuncher, a new β = 0.085 quarter-wave-resonator cryomodule to increase the beam energy from 3 MeV/u to 6 MeV/u for ions with a charge-to-mass ratio of 1/4, and a new experimental vault with beamlines.

Slides WEYE2 [4.220 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEYE2

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Received ※ 13 July 2022 — Revised ※ 01 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 10 August 2022

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WEZD6

Manufacturing the Harmonic Kicker Cavity Prototype for the Electron-Ion Collider

kicker, electron, collider, MMI

601

S.A. Overstreet, M.W. Bruker, G.A. Grose, J. Guo, J. Henry, G.-T. Park, R.A. Rimmer, H. Wang, R.S. Williams
JLab, Newport News, Virginia, USA

Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177
High-bunch-frequency beam-separation schemes, such as the injection scheme proposed for the Rapid Cycling Synchrotron at the Electron-Ion Collider, demand rise and fall times an order of magnitude below what can realistically be accomplished with a stripline kicker. Nanosecond-time-scale kick waveforms can instead be obtained by Fourier synthesis in a harmonically resonant quarter-wave radio-frequency cavity which is optimized for high shunt impedance. Originally developed for the Jefferson Lab Electron-Ion Collider (JLEIC) Circulator Cooler Ring, a hypothetical 11-pass ring driven by an energy-recovery linac at Jefferson Lab, our high-power prototype of such a harmonic kicker cavity, which operates at five modes at the same time, will demonstrate the viability of this concept with a beam test at Jefferson Lab. As the geometry of the cavity, tight mechanical tolerances, and number of ports complicate the design and manufacturing process, special care must be given to the order of the manufacturing steps. We present our experiences with the manufacturability of the present design, lessons learned, and first RF test results from the prototype.

Slides WEZD6 [12.312 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZD6

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Received ※ 04 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 18 August 2022 — Issue date ※ 31 August 2022

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WEZE3

Compact, High-Power Superconducting Electron Linear Accelerators for MW Industrial Applications

electron, SRF, vacuum, gun

604

J.C.T. Thangaraj, R. Dhuley
Fermilab, Batavia, Illinois, USA

Fermilab has developed a novel concept for an industrial electron linac using Nb₃Sn coating technology and conduction cooling. We will show the range of multi-cavity linac designs targeted toward various applications. We will also discuss technology development status with results on conduction cooling of SRF cavities based on cryocoolers, which removes the need for liquid Helium, thus making SRF technology accessible to industrial applications. These conduction-cooled linacs can generate electron beam energies up to 10 MeV in continuous-wave operation and can reach higher power (>=1 MW) by combing several modules. Compact and light enough to mount on mobile platforms, our machine is anticipated to enable new in-situ environmental remediation applications such as waste-water treatment for urban areas, X-ray medical device sterilization, and innovative pavement applications. We also show cost-economics and key R&D areas that much be addressed for a practical machine.

Slides WEZE3 [3.811 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZE3

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Received ※ 02 August 2022 — Revised ※ 12 August 2022 — Accepted ※ 13 August 2022 — Issue date ※ 30 August 2022

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WEZE4

First High-Gradient Results of UED/UEM SRF Gun at Cryogenic Temperatures

gun, SRF, accelerating-gradient, cryogenics

607

R.A. Kostin, C. Jing
Euclid Beamlabs, Bolingbrook, USA
D.J. Bice, T.N. Khabiboulline, S. Posen
Fermilab, Batavia, Illinois, USA

Funding: The project is funded by DOE SBIR #DE-SC0018621
Benefiting from the rapid progress on RF photogun technologies in the past two decades, the development of MeV range ultrafast electron diffraction/microscopy (UED and UEM) has been identified as an enabling instrumentation. UEM or UED use low power electron beams with modest energies of a few MeV to study ultrafast phenomena in a variety of novel and exotic materials. SRF photoguns become a promising candidate to produce highly stable electrons for UEM/UED applications because of the ultrahigh shot-to-shot stability compared to room temperature RF photoguns. SRF technology was prohibitively expensive for industrial use until two recent advancements: Nb₃Sn and conduction cooling. The use of Nb₃Sn allows to operate SRF cavities at higher temperatures (4K) with low power dissipation which is within the reach of commercially available closed-cycle cryocoolers. Euclid is developing a continuous wave (CW), 1.5-cell, MeV-scale SRF conduction cooled photogun operating at 1.3 GHz. In this paper, we present first high gradient results of the gun conducted in liquid helium.

Slides WEZE4 [2.817 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZE4

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Received ※ 05 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 29 September 2022

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WEZE5

Magnetic Flux Expulsion in Superconducting Radio-Frequency Niobium Cavities Made from Cold Worked Niobium

SRF, niobium, radio-frequency, ECR

611

B.D. Khanal
ODU, Norfolk, Virginia, USA
S. Balachandran, P.J. Lee
NHMFL, Tallahassee, Florida, USA
S. Chetri
ASC, Tallahassee, Florida, USA
P. Dhakal
JLab, Newport News, Virginia, USA

Trapped residual magnetic field during the cool down of superconducting radio frequency (SRF) cavities is one of the primary sources of RF residual losses leading to lower quality factor. Historically, SRF cavities have been fabricated from high purity fine grain niobium with grain size ~50 to 100 µm as well as large grain with grain size of the order of few centimeters. Non-uniform recrystallization of fine-grain Nb cavities after the post fabrication heat treatment leads to higher flux trapping during the cool down, and hence the lower quality factor. We fabricated two 1.3 GHz single cell cavities from cold-worked niobium from different vendors and processed along with cavities made from SRF grade Nb. The flux expulsion and flux trapping sensitivity were measured after successive heat treatments in the range 800 to 1000°C. The flux expulsion from cold-worked fine-grain Nb cavities improves after 800°C/3h heat treatments and it becomes similar to that of standard fine-grain Nb cavities when the heat treatment temperature is higher than 900°C.

Slides WEZE5 [2.029 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZE5

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Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 31 August 2022

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WEPA01

Beam Dynamics Optimization of a Low Emittance Photoinjector Without Buncher Cavities

emittance, electron, cathode, gun

615

J. Qiang
LBNL, Berkeley, California, USA
F. Ji, T.O. Raubenheimer
SLAC, Menlo Park, California, USA

The photoinjector plays an important role in generating high brightness low emittance electron beam for x-ray free electron laser applications. In this paper, we report on beam dynamics optimization study of a low emittance photoinjector based on a proposed superconducting gun without including any buncher cavities. Multi-objective optimization with self-consistent beam dynamics simulations was employed to attain the optimal Pareto front.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA01

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Received ※ 02 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 11 September 2022

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WEPA02

Beam Dynamics Studies on a Low Emittance Injector for LCLS-II-HE

emittance, cathode, gun, solenoid

619

F. Ji, C. Adolphsen, R. Coy, L. Ge, C.E. Mayes, T.O. Raubenheimer, L. Xiao
SLAC, Menlo Park, California, USA
J. Qiang
LBNL, Berkeley, California, USA

The SLAC High Energy upgrade of LCLS-II (LCLS-II-HE) will double the beam energy to 8 GeV, increasing the XFEL photon energy reach to about 13 keV. The energy reach can be extended to 20 keV if the beam emittance can be halved, which requires a higher gradient electron gun with a lower intrinsic emittance photocathode. To this end, the Low Emittance Injector (LEI) will be built that will run parallel to the existing LCLS-II Injector. The LEI design will be based on a state-of-the-art SRF gun with a 30 MV/m cathode gradient. The main goal is to produce transverse beam emittances of 0.1 mm-mrad for 100 pC bunch charges. This paper describes the beam dynamics studies on the design of the LEI including the simulations and multi-objective genetic algorithm (MOGA) optimizations. Performance with different injector layouts, cathode gradients, bunch charges and cathode mean transverse energies (MTEs) will be presented.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA02

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Received ※ 02 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 17 August 2022

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WEPA03

Status of the SLAC/MSU SRF Gun Development Project

cathode, gun, SRF, cryomodule

623

J.W. Lewellen, C. Adolphsen, R. Coy, L. Ge, F. Ji, M.J. Murphy, L. Xiao
SLAC, Menlo Park, California, USA
A. Arnold, S. Gatzmaga, P. Murcek, R. Xiang
HZDR, Dresden, Germany
Y. Choi, C. Compton, X.-J. Du, D.B. Greene, W. Hartung, S.H. Kim, T. Konomi, S.J. Miller, D.G. Morris, M.S. Patil, J.T. Popielarski, L. Popielarski, K. Saito, T. Xu
FRIB, East Lansing, Michigan, USA
M.P. Kelly, T.B. Petersen
ANL, Lemont, Illinois, USA

Funding: US Department of Energy.
The LCLS-II-HE project at SLAC is intended to increase the photon energy reach of the LCLS-II FEL to at least 20 keV. In addition to upgrading the undulator system, and increasing the electron beam energy to 8 GeV, the project will also construct a low-emittance injector (LEI) in a new tunnel. To achieve the LEI emittance goals, a low-MTE photocathode will be required, as will on-cathode electric fields up to 50% higher than those achievable in the current LCLS-II photoinjector. The beam source for the LEI will be based around a superconducting quarterwave cavity resonant at 185.7 MHz. A prototype gun is currently being designed and fabricated at the Facility for Rare Isotope Beams (FRIB) at Michigan State University. This paper presents the performance goals for the new gun design, an overview of the prototype development effort, current status, and future plans including fabrication of a "production" gun for the LEI.

Poster WEPA03 [4.510 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA03

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Received ※ 21 July 2022 — Revised ※ 28 July 2022 — Accepted ※ 08 August 2022 — Issue date ※ 11 August 2022

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WEPA09

A Parallel Automatic Simulation Tool for Cavity Shape Optimization

HOM, simulation, SRF, gun

634

L. Ge, Z. Li, C.-K. Ng, L. Xiao
SLAC, Menlo Park, California, USA
M. Beall, B.R. Downie, O. Klaas
Simmetrix Inc., Clifton Park, USA

Funding: U.S. Department of Energy under contract No. DE-SC0018715.
We present a parallel automatic shape optimization workflow for designing accelerator cavities. The newly developed 3D parallel optimization tool Opt3P based on discrete adjoint methods is used to determine the optimal accelerator cavity shape with the desired spectral response. Initial and updated models, meshes, and design velocities of design parameters for defining the cavity shape are generated with Simmetrix tools for mesh generation (MeshSim), geometry modification and query (GeomSim), and user interface tools (SimModeler). Two shape optimization examples using this automatic simulation workflow will be presented here. One is the TESLA cavity with higher-order-mode (HOM) couplers and the other is a superconducting rf (SRF) gun. The objective for the TESLA cavity is to minimize HOM damping factors and for the SRF gun to minimize the surface electric and magnetic fields while maintaining its operating mode frequency at a prescribed value. The results demonstrate that the automatic simulation tool allows an efficient shape optimization procedure with minimal manual operations. All simulations were performed on the NERSC supercomputer Cori system for solution speedup.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA09

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Received ※ 03 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 08 October 2022

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WEPA10

Determination of LCLS-II Gun-2 Prototype Dimensions

gun, cathode, simulation, vacuum

637

L. Xiao, C. Adolphsen, E.N. Jongewaard, X. Liu, F. Zhou
SLAC, Menlo Park, California, USA

The LCLS-II spare gun (Gun-2) design is largely based on the existing LCLS-II gun (Gun-1), in which there is significant captured dark current (DC) that originates on the high field copper surface near the cathode plug gap opening. To help suppress DC, the Gun-2 cathode and anode noses and the cathode plug opening are elliptically shaped to minimize the peak surface field for a given cathode gradient. Stainless steel (SS) cathode and anode inserts are used in Gun-2 to further reduce dark current. The RF simulations were performed using a model that includes all the 3D features. The thermal and structural analyses were done to investigate the effects of the air pressure and RF heating. The multi-physics simulation results provided the information needed to compute the overall frequency change from the basic 2D model to the nominal frequency during operation. The Gun-2 cathode-to-anode gap distance will be made 1 mm longer than the nominal gap with the expectation that less than 1 mm will be machined off to meet the target frequency. In this paper, the Gun-2 frequency correction calculations are presented, and the cathode-to-anode gap determination is discussed.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA10

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Received ※ 30 July 2022 — Revised ※ 03 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 10 August 2022

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WEPA12

Operational Experience of the New Booster Cryomodule at the Upgraded Injector Test Facility

booster, cryomodule, simulation, experiment

640

M.W. Bruker, R. Bachimanchi, J.M. Grames, M.D. McCaughan, J. Musson, P.D. Owen, T.E. Plawski, M. Poelker, T. Powers, H. Wang, Y.W. Wang
JLab, Newport News, Virginia, USA

Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.
Since the early 1990s, the injector of the CEBAF accelerator at Jefferson Lab has relied on a normal-conducting RF graded-beta capture section to boost the kinetic energy of the electron beam from 100 / 130 keV to 600 keV for subsequent acceleration using a cryomodule housing two superconducting 5-cell cavities similar to those used throughout the accelerator. To simplify the injector design and improve the beam quality, the normal-conducting RF capture section and the cryomodule will be replaced with a new single booster cryomodule employing a superconducting, β = 0.6, 2-cell-cavity capture section and a single, β = 0.97, 7-cell cavity. The Upgraded Injector Test Facility at Jefferson Lab is currently hosting the new cryomodule to evaluate its performance with beam before installation at CEBAF. While demonstrating satisfactory performance of the booster and good agreement with simulations, our beam test results also speak to limitations of accelerator operations in a noisy, thermally unregulated environment.

Poster WEPA12 [3.726 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA12

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Received ※ 03 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 06 September 2022

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WEPA19

HE Production Update at JLab - Introducing an Enhanced Nitrogen Purge for Clean String Assembly

controls, cryomodule, vacuum, hardware

659

P.D. Owen
JLab, Newport News, Virginia, USA

A major limitation to cryomodule performance is field emission caused by particulates within the superconducting cavities. To reduce contamination of the inner surfaces during assembly in a cleanroom, the whole string can be connected to a purge system, which maintains a constant overpressure of dry, clean nitrogen gas. Following successes of similar systems at XFEL and Fermilab, Jefferson Lab followed this example for the production of LCLS-II HE cryomodules. Implementing this system required new procedures, infrastructure, and hardware, as well as significant testing of the system before production began. This paper will summarize the implemented controls and procedures, including lessons learned from Fermilab, as well as the results of mock-up tests. Based on the latter, the system was used to assemble the first article string in April 2022, and was also used during a rework required due to issues with cold FPC ceramics two months later. The benefits of using a purge system with regards to procedure, time savings, and added flexibility for potential rework have already proven to provide a significant improvement for the production of LCLS-II-HE cryomodules at Jefferson Lab.

Poster WEPA19 [1.538 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA19

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Received ※ 02 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 21 August 2022

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WEPA23

SRF Cavity Instability Detection with Machine Learning at CEBAF

EPICS, SRF, linac, controls

669

D.L. Turner, R. Bachimanchi, A. Carpenter, J. Latshaw, C. Tennant, L.S. Vidyaratne
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
During the operation of CEBAF, one or more unstable superconducting radio-frequency (SRF) cavities often cause beam loss trips while the unstable cavities themselves do not necessarily trip off. Identifying an unstable cavity out of the hundreds of cavities installed at CEBAF is difficult and time-consuming. The present RF controls for the legacy cavities report at only 1 Hz, which is too slow to detect fast transient instabilities. A fast data acquisition system for the legacy SRF cavities is being developed which samples and reports at 5 kHz to allow for detection of transients. A prototype chassis has been installed and tested in CEBAF. An autoencoder based machine learning model is being developed to identify anomalous SRF cavity behavior. The model is presently being trained on the slow (1 Hz) data that is currently available, and a separate model will be developed and trained using the fast (5 kHz) DAQ data once it becomes available. This paper will discuss the present status of the new fast data acquisition system and results of testing the prototype chassis. This paper will also detail the initial performance metrics of the autoencoder model.

Poster WEPA23 [1.859 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA23

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Received ※ 01 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 24 August 2022

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WEPA25

Field Emission Mitigation in CEBAF SRF Cavities Using Deep Learning

radiation, detector, neutron, linac

676

K. Ahammed, J. Li
ODU, Norfolk, Virginia, USA
A. Carpenter, R. Suleiman, C. Tennant, L.S. Vidyaratne
JLab, Newport News, Virginia, USA

Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.
The Continuous Electron Beam Accelerator Facility (CEBAF) operates hundreds of superconducting radio frequency (SRF) cavities in its two main linear accelerators. Field emission can occur when the cavities are set to high operating RF gradients and is an ongoing operational challenge. This is especially true in newer, higher gradient SRF cavities. Field emission results in damage to accelerator hardware, generates high levels of neutron and gamma radiation, and has deleterious effects on CEBAF operations. So, field emission reduction is imperative for the reliable, high gradient operation of CEBAF that is required by experimenters. Here we explore the use of deep learning architectures via multilayer perceptron to simultaneously model radiation measurements at multiple detectors in response to arbitrary gradient distributions. These models are trained on collected data and could be used to minimize the radiation production through gradient redistribution. This work builds on previous efforts in developing machine learning (ML) models, and is able to produce similar model performance as our previous ML model without requiring knowledge of the field emission onset for each cavity.

Poster WEPA25 [1.586 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA25

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Received ※ 01 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 20 September 2022

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WEPA26

197 MHz Waveguide Loaded Crabbing Cavity Design for the Electron-Ion Collider

HOM, GUI, impedance, electron

679

S.U. De Silva, J.R. Delayen
ODU, Norfolk, Virginia, USA
J. Guo, R.A. Rimmer
JLab, Newport News, Virginia, USA
Z. Li
SLAC, Menlo Park, California, USA
B.P. Xiao
BNL, Upton, New York, USA

The Electron-Ion Collider will require crabbing systems at both hadron and electron storage rings in order to reach the desired luminosity goal. The 197 MHz crab cavity system is one of the critical rf systems of the col-lider. The crab cavity, based on the rf-dipole design, ex-plores the option of waveguide load damping to suppress the higher order modes and meet the tight impedance specifications. The cavity is designed with compact dog-bone waveguides with transitions to rectangular wave-guides and waveguide loads. This paper presents the compact 197 MHz crab cavity design with waveguide damping and other ancillaries.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA26

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Received ※ 08 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 06 September 2022

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WEPA27

Effect of Duration of 120 °C Baking on the Performance of Superconducting Radio Frequency Niobium Cavities

niobium, SRF, radio-frequency, accelerating-gradient

683

B.D. Khanal
ODU, Norfolk, Virginia, USA
P. Dhakal
JLab, Newport News, Virginia, USA

Over the last decade much attention was given in increasing the quality factor of superconducting radio frequency (SRF) cavities by impurity doping. Prior to the era of doping, the final cavity processing technique to achieve the high accelerating gradient includes the "in situ" low temperature baking of SRF cavities at temperature ~ 120°C for several hours. Here, we present the results of a series of measurements on 1.3 GHz TESLA shape single-cell cavities with successive low temperature baking at 120°C up to 96 hours. The experimental data were analyzed with available theory of superconductivity to elucidate the effect of the duration of low temperature baking on the superconducting properties of cavity materials as well as the RF performance. In addition, the RF loss related to the trapping of residual magnetic field refereed as flux trapping sensitivity was measured with respect to the duration of 120°C bake.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA27

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Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 19 August 2022

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WEPA29

Real-Time Cavity Fault Prediction in CEBAF Using Deep Learning

network, cryomodule, SRF, experiment

687

M. Rahman, K.M. Iftekharuddin
ODU, Norfolk, Virginia, USA
A. Carpenter, T.S. McGuckin, C. Tennant, L.S. Vidyaratne
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Data-driven prediction of future faults is a major research area for many industrial applications. In this work, we present a new procedure of real-time fault prediction for superconducting radio-frequency (SRF) cavities at the Continuous Electron Beam Accelerator Facility (CEBAF) using deep learning. CEBAF has been afflicted by frequent downtime caused by SRF cavity faults. We perform fault prediction using pre-fault RF signals from C100-type cryomodules. Using the pre-fault signal information, the new algorithm predicts the type of cavity fault before the actual onset. The early prediction may enable potential mitigation strategies to prevent the fault. In our work, we apply a two-stage fault prediction pipeline. In the first stage, a model distinguishes between faulty and normal signals using a U-Net deep learning architecture. In the second stage of the network, signals flagged as faulty by the first model are classified into one of seven fault types based on learned signatures in the data. Initial results show that our model can successfully predict most fault types 200 ms before onset. We will discuss reasons for poor model performance on specific fault types.

Poster WEPA29 [1.339 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA29

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Received ※ 02 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 17 August 2022

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WEPA30

Nb₃Sn Coating of a 2.6 GHz SRF Cavity by Sputter Deposition Technique

SRF, site, target, plasma

691

M.S. Shakel, W. Cao, H. Elsayed-Ali, Md.N. Sayeed
ODU, Norfolk, Virginia, USA
G.V. Eremeev
Fermilab, Batavia, Illinois, USA
U. Pudasaini, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Funding: Supported by DOE, Office of Accelerator R&D and Production, Contact No. DE-SC0022284, with partial support by DOE, Office of Nuclear Physics DE-AC05-06OR23177, Early Career Award to G. Eremeev.
Nb₃Sn is of interest as a coating for SRF cavities due to its higher transition temperature Tc ~18.3 K and superheating field Hsh ~400 mT, both are twice that of Nb. Nb₃Sn coated cavities can achieve high-quality factors at 4 K and can replace the bulk Nb cavities operated at 2 K. A cylindrical magnetron sputtering system was built, commissioned, and used to deposit Nb₃Sn on the inner surface of a 2.6 GHz single-cell Nb cavity. With two identical cylindrical magnetrons, this system can coat a cavity with high symmetry and uniform thickness. Using Nb-Sn multilayer sequential sputtering followed by annealing at 950°C for 3 hours, polycrystalline Nb₃Sn films were first deposited at the equivalent positions of the cavity’s beam tubes and equator. The film’s composition, crystal structure, and morphology were characterized by energy dispersive spectroscopy, X-ray diffraction, and atomic force microscopy. The Tc of the films was measured by the four-point probe method and was 17.61 to 17.76 K. Based on these studies, ~1.2 micron thick Nb₃Sn was deposited inside a 2.6 GHz Nb cavity. We will discuss first results from samples and cavity coatings, and the status of the coating system.

Poster WEPA30 [1.769 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA30

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Received ※ 03 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 22 August 2022

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WEPA31

Lower Temperature Annealing of Vapor Diffused Nb₃Sn for Accelerator Cavities

SRF, superconductivity, experiment, electron

695

J.K. Tiskumara, J.R. Delayen
ODU, Norfolk, Virginia, USA
G.V. Eremeev
Fermilab, Batavia, Illinois, USA
U. Pudasaini
JLab, Newport News, Virginia, USA

Nb₃Sn is a next-generation superconducting material for the accelerator cavities with higher critical temperature and superheating field, both twice compared to Nb. It promises superior performance and higher operating temperature than Nb, resulting in significant cost reduction. So far, the Sn vapor diffusion method is the most preferred and successful technique to coat niobium cavities with Nb₃Sn. Although several post-coating techniques (chemical, electrochemical, mechanical) have been explored to improve the surface quality of the coated surface, an effective process has yet to be found. Since there are only a few studies on the post-coating heat treatment at lower temperatures, we annealed Nb₃Sn-coated samples at 800 C - 1000 C to study the effect of heat treatments on surface properties, primarily aimed at removing surface Sn residues. This paper discusses the systematic surface analysis of coated samples after annealing at temperatures between 850 C and 950 C.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA31

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Received ※ 02 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 02 September 2022

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WEPA36

Emittance Growth Due to RF Phase Noise in Crab Cavities

emittance, simulation, collider, betatron

708

H. Huang, S. Zhao
ODU, Norfolk, Virginia, USA
F. Lin, V.S. Morozov
ORNL RAD, Oak Ridge, Tennessee, USA
Y. Luo
Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA
T. Satogata, Y. Zhang
JLab, Newport News, Virginia, USA
B.P. Xiao, D. Xu
BNL, Upton, New York, USA

The Electron-Ion Collider (EIC) incorporates beam crabbing to recover geometric luminosity loss from the nonzero crossing angle at the interaction point (IP). It is well-known that crab cavity imperfections can cause growth of colliding beam emittances, thus degrading collider performance. Here we report a particle tracking study to quantify these effects. Presently the study is focused on crab cavity RF phase noise. Simulations were carried out using Bmad. Dependence of emittance growth on phase noise level was obtained which could be used for developing crab cavity phase control specifications. We also benchmarked these simulations with theory.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA36

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Received ※ 02 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 02 September 2022

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WEPA48

Electromagnetic Design of a Compact RF Chopper for Heavy-Ion Beam Separation at FRIB

dipole, linac, simulation, MEBT

738

A.C. Araujo Martinez, R.B. Agustsson, Y.C. Chen, S.V. Kutsaev
RadiaBeam, Santa Monica, California, USA
A.S. Plastun, X. Rao
FRIB, East Lansing, Michigan, USA

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, under SBIR grant DE- SC0020671.
Rare isotope beams are produced at FRIB via fragmentation of a primary heavy ion beam in a thin target. The isotope beam of interest is contaminated with other fragments, which must be filtered out to ensure the delivery of rare isotopes with desired rates and purities. One of the stages of fragment separation uses an RF deflecting cavity to provide time-of-flight separation. However, to avoid neighboring bunches overlapping with each other and with the contaminants, it is necessary to increase the inter-bunch distance by a factor of four, corresponding to a 20.125 MHz rate. To solve this problem, we have developed an RF chopper system for the 500 keV/u primary heavy-ion beams. The system consists of a deflecting quarter wave resonator (QWR) cavity operating at 60.375 MHz, two dipole steering magnets, and a beam dump. In this paper, we present and discuss the optimization of the electromagnetic design of the QWR cavity and magnets, as well as some aspects, related to beam dynamics and conceptual engineering design.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA48

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Received ※ 02 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 08 September 2022

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WEPA49

Ferrite-Free Circulator for Precise Measurements of SRF Cavities with High Q-Factor

ISOL, SRF, resonance, experiment

742

A.I. Pronikov, A.Yu. Smirnov
RadiaBeam, Santa Monica, California, USA
A.A. Krasnok
Florida International University, Miami, Florida, USA
S.N. Romanenko
Zaporizhzhya National Technical University, Zaporizhzhya, Ukraine
V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Funding: This work was supported by the US Department of Energy, Offices of High Energy and Nuclear Physics, awards DE-SC0020926 and DE-SC0022439.
In this work, we suggest and investigate new magnetless circulators based on three resonators connected in a loop and parametrically modulated in time with mutual phase lag. The first design consists of three Fano resonators with a spectrally asymmetric response, in contrast to schemes based on the Lorentz resonators explored thus far. The second design includes three Fano-Lorentz resonators, i.e., it also possesses spatial asymmetry. We demonstrate that the asymmetric approach provides strong and reversible isolation for the practically feasible modulation amplitude and rate. The results of our work are promising for precise measurements of superconducting radio frequency cavities with high Q-factor.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA49

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Received ※ 04 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 13 September 2022

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WEPA52

Demonstration of Twice-Reduced Lorentz-Force Detuning in SRF Cavity by Copper Cold Spraying

SRF, site, niobium, accelerating-gradient

749

R.A. Kostin, C.-J. Jing, A. Kanareykin
Euclid TechLabs, Solon, Ohio, USA
G. Ciovati
JLab, Newport News, Virginia, USA

Funding: The project is funded by DOE SBIR # DE-SC0019589
Superconducting RF (SRF) cavities usually are made from thin-walled high RRR Niobium and are susceptible to Lorentz Force Detuning (LFD) ’ cavity deformation phenomena by RF fields. In this paper, we present high gradient cryogenic results of an SRF cavity with two times reduced LFD achieved by copper cold spray reinforcement without sacrificing cavity flexibility for tuning. Finite-element model was developed first to find the best geometry for LFD reduction, which incorporated coupled RF, structural and thermal modules, and is also presented.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA52

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Received ※ 27 July 2022 — Revised ※ 03 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 16 August 2022

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WEPA55

Applications of Machine Automation with Robotics and Computer Vision in Cleanroom Assemblies

controls, SRF, operation, vacuum

756

A. Liu, J.R. Callahan, E. Gomez, S.M. Milller, W. Si
Euclid TechLabs, Solon, Ohio, USA

Funding: This work is supported by the US DOE SBIR program under contract number DE-SC0021736.
Modern linear particle accelerators use superconducting radio frequency (SRF) cavities for achieving extremely high-quality factors (Q) and higher beam stability. The assembly process of the system, although with a much more stringent cleanness requirement, is very similar to the ultrahigh vacuum (UHV) system operation procedure. Humans, who are conventionally the operators in this procedure, can only avoid contaminating the system by wearing proper sterile personal protection equipment to avoid direct skin contact with the systems, or dropping particulates. However, humans unavoidably make unintentional mistakes that can contaminate the environment: cross contamination of the coverall suits during wearing, slippage of masks or goggles, damaged gloves, and so forth. Besides, humans are limited when operating heavy weights, which may lead to incorrect procedures, or even worse, injury. In this paper, we present our recent work on a viable and cost-effective machine automation system composed of a robotic arm and a computer vision system for the assembly process in a cleanroom environment, for example for SRF string assemblies, and more.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA55

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Received ※ 30 July 2022 — Revised ※ 04 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 12 August 2022

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WEPA63

Extensions of the Complex (IQ) Baseband RF Cavity Model Including RF Source and Beam Interactions

controls, simulation, beam-loading, linac

767

S.P. Jachim, B.J. Cook, J.R.S. Falconer
Arizona State University, Tempe, USA

Funding: This work was supported in part by NSF award #1935994.
This paper extends prior work describing a complex envelope (i.e., baseband) dynamic model of excited accelerator RF cavities, including the effects of frequency detuning, beam loading, reflections, multiple drive ports, and parasitic modes. This model is presented here in closed-form transfer function and state-variable realizations, which may be more appropriate for analytic purposes. Several example simulations illustrate the detailed insight into RF system behavior afforded by this model.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA63

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Received ※ 28 July 2022 — Revised ※ 08 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 15 August 2022

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WEPA69

The Impact on the Vertical Beam Dynamics Due to the Noise in a Horizontal Crab Crossing Scheme

emittance, feedback, electron, hadron

788

Y. Hao
BNL, Upton, New York, USA
Y. Luo
Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA

Funding: Work Supported BY Brookhaven Science Associates, LLC under contract NO. DE-SC0012704 with the U.S. Department of Energy.
Several recent and future colliders have adopted the crab crossing scheme to boost performance. The lower RF control noise of the crab cavities has been identified as one of the significant sources that impact the transverse beam quality in the crabbing plane. However, through beam-beam interaction and other coupling sources, the effect may also affect the non-crabbing plane. In this paper, we report the simulation observations of the beam dynamics in the non-crabbing plane in the presence of phase noise in the crab cavity.

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA69

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Received ※ 03 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 06 September 2022

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WEPA75

{6-D} Element-by-Element Particle Tracking with Crab Cavity Phase Noise and Weak-Strong Beam-Beam Interaction for the Hadron Storage Ring of the Electron-Ion Collider

emittance, simulation, proton, electron

809

Y. Luo, J.S. Berg, M. Blaskiewicz, C. Montag, V. Ptitsyn, F.J. Willeke, D. Xu
BNL, Upton, New York, USA
Y. Hao
FRIB, East Lansing, Michigan, USA
H. Huang
ODU, Norfolk, Virginia, USA
V.S. Morozov
ORNL RAD, Oak Ridge, Tennessee, USA
J. Qiang
LBNL, Berkeley, California, USA
T. Satogata
JLab, Newport News, Virginia, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
The Electron Ion Collider (EIC) presently under construction at Brookhaven National Laboratory will collide polarized high energy electron beams with hadron beams with luminosity up to 10³⁴ cm^-2 s^-1 in the center mass energy range of 20 to 140 GeV. Crab cavities are used to compensate the geometric luminosity due to a large crossing angle in the EIC. However, it was found that the phase noise in crab cavities will generate a significant emittance growth for hadron beams and its tolerance from analytical calculation is very small for the Hadron Storage Ring (HSR) of the EIC. In this paper, we report on 6-D symplectic particle tracking to estimate the proton emittance growth rate, especially in the vertical plane, for the HSR with weak-strong beam-beam and other machine or lattice errors.

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA75

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Received ※ 01 August 2022 — Revised ※ 06 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 19 August 2022

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THXD6

A Quasi-Optical Beam Position Monitor

coupling, electron, site, photon

846

S.V. Kuzikov
Euclid TechLabs, Solon, Ohio, USA

There is a strong demand for non-destructive electron Beam Position Monitors (BPMs) for non-perturbative diagnostics of the electron beam position. Challenges are related to the shortness of the electron beam and the noisy chamber environment that are typical for modern RF-driven and plasma-driven accelerators. We propose using a pair of identical high-quality quasi-optical resonators attached to opposite sides of the beam pipe. The resonators can introduce Photonic Band Gap (BPM) structures. These open resonators sustain very low numbers of high-quality modes. We intend to operate at the lowest mode among the others that are capable of being excited by the bunches. The mentioned mode has a coupling coefficient with the beam that depends on the distance between the bunch and the coupling hole. The lower this distance, the higher the coupling. Therefore, comparing the pick-up signals of both resonators with an oscilloscope, we can determine the beam position.

Slides THXD6 [3.745 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THXD6

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Received ※ 25 July 2022 — Accepted ※ 06 August 2022 — Issue date ※ 27 September 2022

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THYD3

Update on the Status of C-Band Research and Facilities at LANL

cathode, electron, klystron, operation

855

E.I. Simakov, A.M. Alexander, D.V. Gorelov, T.W. Hall, M.E. Middendorf, D. Rai, T. Tajima, M.R.A. Zuboraj
LANL, Los Alamos, New Mexico, USA

Funding: Los Alamos National Laboratory LDRD Program
We will report on the status of two C-band test facilities at Los Alamos National Laboratory (LANL): C-band Engineering Research Facility in New Mexico (CERF-NM), and Cathodes and Rf Interactions in Extremes (CARIE). Modern applications such as X-ray sources require accelerators with optimized cost of construction and operation, naturally calling for high-gradient acceleration. At LANL we commissioned a high gradient test stand powered by a 50 MW, 5.712 GHz Canon klystron. CERF-NM is the first high gradient C-band test facility in the United States. It was fully commissioned in 2021. In the last year, multiple C-band high gradient cavities and components were tested at CERF-NM. Currently we work to implement several updates to the test stand including the ability to remotedly operate at high gradient for the round-the-clock high gradient conditioning. Adding capability to operate at cryogenic temperatures is considered. The construction of CARIE will begin in October of 2022. CARIE will house a cryo-cooled copper RF photoinjector with a high quantum-efficiency cathode and a high gradient accelerator section.

Slides THYD3 [3.331 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYD3

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Received ※ 31 July 2022 — Revised ※ 08 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 04 October 2022

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THYD6

Arrival Time and Energy Jitter Effects on the Performance of X-Ray Free Electron Laser Oscillator

FEL, electron, laser, radiation

866

G. Tiwari
BNL, Upton, New York, USA
K.-J. Kim, R.R. Lindberg
ANL, Lemont, Illinois, USA
K.-J. Kim
University of Chicago, Chicago, Illinois, USA

Funding: U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357.
We report on the effects of electron beam arrival time and energy jitter on the power level and the fluctuations of the output of an X-ray FEL oscillator (XFELO). For this study, we apply the FEL driven paraxial resonator model of XFELO along with an analytical reflectivity profile to mimic the phase shift and spectral filtering effects of Bragg-crystals. The thresholds for acceptable timing jitters and energy jitters are determined in terms of the fluctuations of the steady-state power output. We explore potential ways to mitigate the power output fluctuations in the presence of unavoidable electron beam jitters.

Slides THYD6 [1.935 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYD6

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Received ※ 01 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 03 October 2022

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THYE5

Analysis of Low RRR SRF Cavities

SRF, niobium, accelerating-gradient, radio-frequency

877

K. Howard, Y.K. Kim
University of Chicago, Chicago, Illinois, USA
D. Bafia, A. Grassellino
Fermilab, Batavia, Illinois, USA

Recent findings in the superconducting radio-frequency (SRF) community have shown that introducing certain impurities into high-purity niobium can improve quality factors and accelerating gradients. Success has been found in nitrogen-doping, diffusion of the native oxide into the niobium surface, and thin films of alternate superconductors atop a niobium bulk cavity. We question why some impurities improve RF performance while others hinder it. The purpose of this study is to characterize the impurity profile of niobium with a low residual resistance ratio (RRR) and correlate these impurities with the RF performance of low RRR cavities so that the mechanism of recent impurity-based improvements can be better understood and improved upon. Additionally, we performed surface treatments, low temperature baking and nitrogen-doping, on low RRR cavities to evaluate how the intentional addition of more impurities to the RF layer affects performance. We have found that low RRR cavities experience low temperature-dependent BCS resistance behavior more prominently than their high RRR counterparts. The results of this study have the potential to unlock a new understanding on SRF materials.

Slides THYE5 [5.013 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYE5

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Received ※ 03 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 01 October 2022

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THYE6

First Demonstration of a ZrNb Alloyed Surface for Superconducting Radio-Frequency Cavities

SRF, radio-frequency, electron, superconductivity

881

Z. Sun, M. Liepe, T.E. Oseroff
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Surface design of the RF surface is a promising path to next-generation SRF cavities. Here, we report a new strategy based on ZrNb surface alloying. Material development via an electrochemical process will be detailed. RF performance evaluated in the Cornell sample host cavity will be discussed. Cornell demonstrates that ZrNb alloying is a viable new technology to improve the performance of SRF cavities.

Slides THYE6 [1.459 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYE6

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Received ※ 22 July 2022 — Accepted ※ 08 August 2022 — Issue date ※ 20 August 2022

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THZD1

Instant Phase Setting in a Large Superconducting Linac

linac, SRF, experiment, MMI

885

A.S. Plastun, P.N. Ostroumov
FRIB, East Lansing, Michigan, USA

Funding: This work is supported by the U.S. Department of Energy Office of Science under Cooperative Agreement No. DE-SC0000661, the State of Michigan, and Michigan State University.
The instant phase setting reduces the time needed to setup 328 radiofrequency cavities of the Facility for Rare Isotope Beams (FRIB) linac from 20 hours to 10 minutes. This technique uses a 1-D computer model of the linac to predict the cavities’ phases. The model has been accurately calibrated using the data of the 360-degree phase scans - a common procedure for phasing of linear accelerators. The model was validated by comparison with a conventional phase scan results. The predictions applied to the linac are then verified by multiple time-of-flight energy measurements and the response of the beam position/phase monitors (BPMs) to an intentional energy and phase mismatch. The presented approach not just reduces the time and the effort required to tune the FRIB accelerator for new experiments every couple of weeks, but it also provides an easy recovery from cavity failures. It is beneficial for user facilities requiring high beam availability, as well as for radioactive ion beam accelerators, where quick time-of-flight energy measurement via the BPMs is not possible due to the low intensities of these beams.

Slides THZD1 [2.610 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THZD1

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Received ※ 07 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 21 August 2022

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THZD4

Accelerating Structures for High-Gradient Proton Radiography Booster at LANSCE

booster, linac, proton, distributed

894

S.S. Kurennoy, Y.K. Batygin, E.R. Olivas
LANL, Los Alamos, New Mexico, USA

Increasing energy of proton beam at LANSCE from 800 MeV to 3 GeV improves radiography resolution ~10 times. We proposed accomplishing such an energy boost with a compact cost-effective linac based on normal conducting high-gradient (HG) RF accelerating structures. Such an unusual proton linac is feasible for proton radiography (pRad), which operates with short RF pulses. For a compact pRad booster at LANSCE, we have developed a multi-stage design: a short L-band section to capture and compress the 800-MeV proton beam followed by the main HG linac based on S- and C-band cavities, and finally, by an L-band de-buncher [1]. Here we present details of development, including EM and thermal-stress analysis, of proton HG structures with distributed RF coupling for the pRad booster. A simple two-cell structure with distributed coupling is being fabricated and will be tested at the LANL C-band RF Test Stand.
[1] S.S. Kurennoy, Y.K. Batygin. IPAC21, MOPAB210.

Slides THZD4 [1.591 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THZD4

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Received ※ 01 August 2022 — Revised ※ 10 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 26 September 2022

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THZD6

An 8 GeV Linac as the Booster Replacement in the Fermilab Power Upgrade

linac, injection, cryomodule, SRF

897

D.V. Neuffer, S.A. Belomestnykh, M. Checchin, D.E. Johnson, S. Posen, E. Pozdeyev, V.S. Pronskikh, A. Saini, N. Solyak, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Funding: Work supported by the Fermi National Accelerator Laboratory, managed and operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy.
Increasing the Main Injector (MI) beam power above ~1.2 MW requires replacement of the 8-GeV Booster by a higher intensity alternative. In the Project X era, rapid-cycling synchrotron (RCS) and linac solutions were considered for this purpose. In this paper, we consider the linac version that produces 8 GeV H⁻ beam for injection into the Recycler Ring (RR) or Main Injector (MI). The linac takes ~1-GeV beam from the PIP-II Linac and accelerates it to ~2 GeV in a 650-MHz SRF linac, followed by a 8-GeV pulsed linac using 1300 MHz cryomodules. The linac components incorporate recent improvements in SRF technology. Research needed to implement the high power SRF Linac is described.

Slides THZD6 [4.078 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THZD6

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Received ※ 03 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 04 October 2022

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FRXD6

Bunch Length Measurements at the CEBAF Injector at 130 kV

laser, electron, simulation, gun

917

S. Pokharel, G.A. Krafft
ODU, Norfolk, Virginia, USA
M.W. Bruker, J.M. Grames, A.S. Hofler, R. Kazimi, G.A. Krafft, S. Zhang
JLab, Newport News, Virginia, USA

Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.
In this work, we investigated the evolution in bunch length of beams through the CEBAF injector for low to high charge per bunch. Using the General Particle Tracer (GPT), we have simulated the beams through the beamline of the CEBAF injector and analyzed the beam to get the bunch lengths at the location of chopper. We performed these simulations with the existing injector using a 130 kV gun voltage. Finally, we describe measurements to validate these simulations. The measurements have been done using chopper scanning technique for two injector laser drive frequency modes: one with 500 MHz, and another with 250 MHz.

Slides FRXD6 [0.800 MB]

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reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-FRXD6

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Received ※ 02 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 01 September 2022

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