02: Photon Sources and Electron Accelerators
Paper Title Page
MOODE2
Expanding the Boundaries of X-ray Lasers: LCLS Upgrades and Future  
 
  • G.R. Hays
    SLAC, Menlo Park, California, USA
 
  The Linac Coherent Light Source (LCLS) is currently in the midst of several major upgrades: LCLS-II, LCLS-II-HE, and MEC-U. These upgrades will augment the facility with a 4 GeV continuous-wave superconducting electron accelerator (LCLS-II) that is subsequently extended to 8 GeV (LCLS-II-HE), and a PW-class laser system coupled to the X-ray laser (MEC-U). The science motivation, expected performance, technological drivers, and status will be presented. Future capabilities, beyond those enabled with the ongoing upgrades, will also be discussed.  
slides icon Slides MOODE2 [3.267 MB]  
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MOZD1
Commissioning of LCLS-II  
 
  • Y. Ding
    SLAC, Menlo Park, California, USA
 
  The LCLS-II is a CW FEL based on a 4 GeV SRF linac. Commissioning of the CW Electron Gun and SRF linac was begun during the winter of 2022 with expectations of 1st light during Summer 2022. Results will be presented.  
slides icon Slides MOZD1 [9.598 MB]  
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MOZD2 Preliminary Study of a High Gain THz FEL in a Recirculating Cavity 30
 
  • A.C. Fisher, P. Musumeci
    UCLA, Los Angeles, California, USA
 
  The THz gap is a region of the electromagnetic spectrum where high average and peak power radiation sources are scarce while at the same time scientific and industrial applications are growing in demand. Free-electron laser coupling in a magnetic undulator is one of the best options for radiation generation in this frequency range, but slippage effects require the use of relatively long and low current electron bunches to drive the THz FEL, limiting amplification gain and output peak power. Here we use a circular waveguide in a 0.96 m strongly tapered helical undulator to match the radiation and e-beam velocities, allowing resonant energy extraction from an ultrashort 200 pC 5.5 MeV electron beam over an extended distance. E-beam energy measurements, supported by energy and spectral measurement of the THz FEL radiation, indicate an average energy efficiency of ~ 10%, with some particles losing > 20% of their initial kinetic energy.  
slides icon Slides MOZD2 [7.005 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOZD2  
About • Received ※ 04 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 13 August 2022
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MOZD3
Development of Two-Color Sub-Femtosecond Pump/Probe Techniques with X-Ray Free-Electron Lasers  
 
  • Z.H. Guo, P.L. Franz
    Stanford University, Stanford, California, USA
  • D.B. Cesar, J.P. Cryan, T.D.C. Driver, J.P. Duris, Z. Huang, K. Larsen, S. Li, A. Marinelli, J.T. O’Neal, R. Robles, N.S. Sudar, A.L. Wang, Z. Zhang
    SLAC, Menlo Park, California, USA
 
  Funding: This work is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), Accelerator and Detector research program.
We report the generation of GW-level attosecond pump/probe pulse pairs with tunable sub-femtosecond delays at the Linac Coherent Light Source (LCLS). The attosecond 370 eV pump pulse is first generated via the Enhanced Self-Amplified Spontaneous Emission (ESASE) method, then the attosecond 740 eV probe pulse is produced by re-amplifying the electron beam microbunching after the magnetic chicane. Due to the harmonic amplification, the minimal delay between pump-probe pulse pairs (limited by slippage between the light field and the electron bunch) can be shorter than 1 femtosecond. We use the angular streaking technique to measure temporal delays between pump/probe pulse pairs at multiple beamline configurations. When the delay chicane is turned off, the averaged delay is increased by ~150 attoseconds by adding one undulator module for probe pulses. Long delays can be set up by turning the delay chicane on. These experimental results are in agreement with start-to-end XFEL simulations. Looking toward future experiments, our sub-femtosecond pump/probe technique can be applied to observe electronic charge dynamics in molecular systems.
 
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MOZD4 Uncertainty Quantification of Beam Parameters in a Linear Induction Accelerator Inferred from Bayesian Analysis of Solenoid Scans 34
 
  • M.A. Jaworski, D.C. Moir, S. Szustkowski
    LANL, Los Alamos, New Mexico, USA
 
  Linear induction accelerators (LIAs) such as the DARHT at Los Alamos National Laboratory make use of the beam envelope equation to simulate the beam and design experiments. Accepted practice is to infer beam parameters using the solenoid scan technique with optical transition radiation (OTR) beam profiles. These scans are then analyzed with an envelope equation solver to find a solution consistent with the data and machine parameters (beam energy, current, magnetic field, and geometry). The most common code for this purpose with flash-radiography LIAs is xtr [1]. The code assumes the machine parameters are perfectly known and that beam profiles will follow a normal distribution about the best fit and solves by minimizing a chi-square-like metric. We construct a Bayesian model of the beam parameters allowing maching parameters, such as solenoid position, to vary within reasonable uncertainty bounds. Posterior distribution functions are constructed using Markov-Chain Monte Carlo (MCMC) methods to evaluate the accuracy of the xtr solution uncertainties and the impact of finite precision in measurements.
[1] P.W. Allison, "Beam dynamics equations for xtr," Los Alamos Technical Report LA-UR-01-6585. November 2001.
 
slides icon Slides MOZD4 [1.082 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOZD4  
About • Received ※ 05 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 20 August 2022
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MOZD5 ERL-Based Compact X-Ray FEL 37
 
  • F. Lin, V.S. Morozov
    ORNL RAD, Oak Ridge, Tennessee, USA
  • J. Guo, Y. Zhang
    JLab, Newport News, Virginia, USA
 
  Funding: Work supported by UT-Battelle, LLC, under contract DE-AC05-00OR22725, and by Jefferson Science Associates, LLC, under contract DE-AC05-06OR23177
We propose to develop an energy-recovery-linac (ERL)-based X-ray free-electron laser (XFEL). Taking advantage of the demonstrated high-efficiency energy recovery of the beam power in the ERL, the proposed concept offers the following benefits: i) recirculating the electron beam through high-gradient superconducting RF (SRF) cavities shortens the linac, ii) energy recovery in the SRF linac saves the klystron power and reduces the beam dump power, iii) the high average beam power produces a high average photon brightness. In addition, such a concept has the capability of delivering optimized high-brightness CW X-ray FEL performance at different energies with simultaneous multipole sources. In this paper, we will present the preliminary results on the study of feasibility, optics design and parameter optimization of such a device.
 
slides icon Slides MOZD5 [2.870 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOZD5  
About • Received ※ 02 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 04 August 2022 — Issue date ※ 11 September 2022
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MOZD6 Accelerator Physics Lessons from CBETA, the First Multi-Turn SRF ERL 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 icon 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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MOPA34 Noise in Intense Electron Bunches 128
 
  • S. Nagaitsev, D.R. Broemmelsiek, J.D. Jarvis, A.H. Lumpkin, J. Ruan, G.W. Saewert, R.M. Thurman-Keup
    Fermilab, Batavia, Illinois, USA
  • Z. Huang, G. Stupakov
    SLAC, Menlo Park, California, USA
  • Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
 
  We report on our investigations into density fluctuations in electron bunches. Noise and density fluctuations in relativistic electron bunches, accelerated in a linac, are of critical importance to various Coherent Electron Cooling (CEC) concepts as well as to free-electron lasers (FELs). For CEC, the beam noise results in additional diffusion that counteracts cooling. In SASE FELs, a microwave instability starts from the initial noise in the beam and eventually leads to the beam microbunching yielding coherent radiation, and the initial noise in the FEL bandwidth plays a useful role. In seeded FELs, in contrast, such noise interferes with the seed signal, so that reducing noise at the initial seed wavelength would lower the seed laser power requirement. Status of the project will be presented.  
poster icon Poster MOPA34 [0.638 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA34  
About • Received ※ 10 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 14 August 2022 — Issue date ※ 24 August 2022
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MOPA46 Cryogenic Dielectric Structure with GΩ/m Level Shunt Impedance 157
 
  • R.A. Kostin, C. Jing
    Euclid Beamlabs, Bolingbrook, USA
 
  Shunt impedance is one of the most important parameters characterizing particle acceleration efficiency. It is known that RF losses are reduced at cryogenic temperatures. For example, a record high shunt impedance of 350 MΩ/m was demonstrated recently for all metal X-band accelerating structure, which is more than 2 times higher than that at room temperature. In this article we present a novel hybrid dielectric structure which can achieve even higher shunt impedance due to the fact that losses in dielectric materials reduced much more than in pure copper.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA46  
About • Received ※ 12 August 2022 — Revised ※ 16 August 2022 — Accepted ※ 23 August 2022 — Issue date ※ 17 September 2022
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MOPA50 Integrated Photonics Structure Cathodes for Longitudinally Shaped Bunch Trains 160
 
  • S.J. Coleman, D.T. Abell, C.C. Hall
    RadiaSoft LLC, Boulder, Colorado, USA
  • R. Kapadia
    University of Southern California, Los Angeles, California, USA
  • S.S. Karkare
    Arizona State University, Tempe, USA
  • S.Y. Kim, P. Piot, J.F. Power
    ANL, Lemont, Illinois, USA
 
  Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Award Number DOE DE-SC0021681
Compact, high-gradient structure wakefield accelerators can operate at improved efficiency using shaped electron beams, such as a high transformer ratio beam shape, to drive the wakes. These shapes have generally come from a photocathode gun followed by a transverse mask to imprint a desired shape on the transverse distribution, and then an emittance exchanger (EEX) to convert that transverse shape into a longitudinal distribution. This process discards some large fraction of the beam, limiting wall-plug efficiency as well as leaving a solid object in the path of the beam. In this paper, we present a proposed method of using integrated photonics structures to control the emission pattern on the cathode surface. This transverse pattern is then converted into a longitudinal pattern at the end of an EEX. This removes the need for the mask, preserving the total charge produced at the cathode surface. We present simulations of an experimental set-up to demonstrate this concept at the Argonne Wakefield Accelerator.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA50  
About • Received ※ 03 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 26 August 2022 — Issue date ※ 03 October 2022
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MOPA79 Studying the Emission Characteristics of Field Emission Cathodes with Various Geometries 226
 
  • M.R. Howard, S.M. Lidia
    FRIB, East Lansing, Michigan, USA
  • J.E. Coleman
    LANL, Los Alamos, New Mexico, USA
 
  Funding: Work supported by the NNSA of US DOE under contract 89233218CNA000001 and partially supported by the US DOE under Cooperative Agreement award number DE-SC0018362 and Michigan State University.
The cathode test stand (CTS) at LANL is designed to hold off voltages of up to 500kV and can supply pulse durations up to 2.6 μs. Using this test stand, we are able to test both field emission and photocathodes with different geometries and materials at various pulse lengths and PFN voltages. Currently, the test stand is used to evaluate field emission using a velvet cathode over various pulse lengths. The CTS employs various diagnostic tools, including E-dots, B-dots, and a scintillator coupled with a pepperpot mask in order to measure the extracted voltage, current, beam distribution, and transverse emittance. Xenos [1] has been used to create and simulate diode geometries that permits study to optimize various beam parameters. These geometries include changing the size and recess of the cathode as well as implementing a Pierce geometry. Here, we will discuss comparisons for various simulated cathodes and how changes in geometry impact given beam parameters.
[1] See https://www.fieldp.com/xenos.html for information about the Xenos software.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA79  
About • Received ※ 02 August 2022 — Revised ※ 10 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 30 August 2022
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TUYD1
High Voltage DC Gun for High Intensity Polarized Electron Source  
 
  • O.H. Rahman, J.P. Biswas, C.M. Degen, W. Liu, J. Skarita, E. Wang
    BNL, Upton, New York, USA
 
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
At Brookhaven National Lab, we have constructed a high intensity polarized electron gun with an inverted electrode geometry and large cathode area. The DC gun showed stable operation at 300 KV with bunch charge up to 16 nC. It also incorporates new technologies such as an active cathode cooling system, a biased anode, and a unique high voltage cable with a semiconductor jacket. Lifetime tests with a biased anode has showed exceptional performance. This gun exceeds EIC polarized gun requirements — high voltage, bunch charge, average current and charge lifetime — with ease. In this talk, we report on the design and performance of the gun including high voltage performance and cathode lifetime tests.
 
slides icon Slides TUYD1 [2.226 MB]  
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TUYD2
Progress Towards Long-Lifetime, High-Current Polarized-Electron Sources  
 
  • J.P. Biswas
    Stony Brook University, Stony Brook, USA
  • J.P. Biswas, M. Gaowei, W. Liu, O.H. Rahman, J.T. Sadowski, X. Tong, E. Wang
    BNL, Upton, New York, USA
 
  Funding: The work was supported by the U.S. Department of Energy under Contract No. DE-AC02-98CH10886
We describe new activation techniques, developed using Cs-Te and Cs-O-Te as a activation layers, to achieve Negative Electron Affinity (NEA) surfaces of GaAs. X-Ray photoelectron spectroscopic and Low Energy Electron Microscopic studies have been performed on these surfaces. The results indicate that both layers achieve NEA of GaAs and lead to longer charge lifetime compared to traditional Cs-O/GaAs photocathodes.
 
slides icon Slides TUYD2 [10.825 MB]  
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TUYD3 The Quest for the Perfect Cathode 281
 
  • J.W. Lewellen, J. Smedley, T. Vecchione
    SLAC, Menlo Park, California, USA
  • D. Filippetto
    LBNL, Berkeley, California, USA
  • S.S. Karkare
    Arizona State University, Tempe, USA
  • J.M. Maxson
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • P. Musumeci
    UCLA, Los Angeles, California, USA
 
  Funding: U.S. Department of Energy.
The next generation of free electron lasers will be the first to see the performance of the laser strongly dependent on the materials properties of the photocathode. A new injector proposed for the LCLS-II HE is an example of this revolution, with the goal of increasing the photon energy achievable by LCLS-II to over 20 keV. We must now ask, what is the optimal cathode, temperature, and laser combination to enable this injector? There are many competing requirements. The cathode must be robust enough to operate in a superconducting injector, and must not cause contamination of the injector. It must achieve sufficient charge at high repetition rate, while minimizing the emittance. The wavelength chosen must minimize mean transverse energy while maintaining tolerable levels of multi-photon emission. The cathode must be capable of operating at high (~30 MV/m) gradient, which puts limits on both surface roughness and field emission. This presentation will discuss the trade space for such a cathode/laser combination, and detail a new collaborative program among a variety of institutions to investigate it.
 
slides icon Slides TUYD3 [1.632 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUYD3  
About • Received ※ 02 August 2022 — Revised ※ 04 August 2022 — Accepted ※ 14 August 2022 — Issue date ※ 26 September 2022
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TUYD4 Towards High Brightness from Plasmon-Enhanced Photoemitters 285
 
  • C.M. Pierce, I.V. Bazarov, J.M. Maxson
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • D.B. Durham, D. Filippetto, F. Riminucci
    LBNL, Berkeley, USA
  • A.H. Kachwala, S.S. Karkare
    Arizona State University, Tempe, USA
  • A. Minor
    UC Berkeley, Berkeley, California, USA
 
  Funding: This work is supported by DOE BES Contract No. DE-AC02-05CH11231. C.P. acknowledges NSF Award PHY-1549132 (CBB) and the US DOE SCGSR program. DD was supported by NSF Grant No. DMR-1548924 (STROBE).
Plasmonic cathodes, whose nanoscale features may locally enhance optical energy from the driving laser trapped at the vacuum interface, have emerged as a promising technology for improving the brightness of metal cathodes. A six orders of magnitude improvement [1] in the non-linear yield of metals has been experimentally demonstrated through this type of nanopatterning. Further, nanoscale lens structures may focus light below its free-space wavelength offering multiphoton photoemission from a region near 10 times smaller [2] than that achievable in typical photoinjectors. In this proceeding, we report on our efforts to characterize the brightness of two plasmonic cathode concepts: a spiral lens and a nanogroove array. We demonstrate an ability to engineer and fabricate nanoscale patterned cathodes by comparing their optical properties with those computed with a finite difference time domain (FDTD) code. The emittance and nonlinear yield of the cathodes are measured under ultrafast laser irradiation. Finally, prospects of this technology for the control and acceleration of charged particle beams are discussed.
[1] Polyakov, A., et al. (2013). Physical Review Letters, 110(7), 076802.
[2] Durham, D. B., et al. (2019). Physical Review Applied, 12(5), 054057.
 
slides icon Slides TUYD4 [7.160 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUYD4  
About • Received ※ 05 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 13 September 2022
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TUYD5 Epitaxial Alkali-Antimonide Photocathodes on Lattice-matched Substrates 289
 
  • P. Saha, S.S. Karkare
    Arizona State University, Tempe, USA
  • E. Echeverria, A. Galdi, J.M. Maxson, C.A. Pennington
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • E.J. Montgomery, S. Poddar
    Euclid Beamlabs, Bolingbrook, USA
 
  Alkali-antimonides photocathodes, characterized by high quantum efficiency (QE) and low mean transverse energy (MTE) in the visible range of spectrum, are excellent candidates for electron sources to drive X-ray Free Electron Lasers (XFEL) and Ultrafast Electron Diffraction (UED). A key figure of merit for these applications is the electron beam brightness, which is inversely proportional to MTE. MTE can be limited by nanoscale surface roughness. Recently, we have demonstrated physically and chemically smooth Cs3Sb cathodes on Strontium Titanate (STO) substrates grown via co-deposition technique. Such flat cathodes could result from a more ordered growth. In this paper, we present RHEED data of co-deposited Cs3Sb cathodes on STO. Efforts to achieve epitaxial growth of Cs3Sb on STO are then demonstrated via RHEED. We find that films grown epitaxially on substrates like STO and SiC (previously used to achieve single crystalline Cs3Sb) exhibit QE higher than the polycrystalline Cs3Sb cathodes, by an order of magnitude below photoemission threshold. Given the larger QE, lower laser fluence could be used to extract high charge densities, thereby leading to enhanced beam brightness.  
slides icon Slides TUYD5 [2.088 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUYD5  
About • Received ※ 01 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 07 September 2022
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TUYD6 Design of a 200 kV DC Cryocooled Photoemission Gun for Photocathode Investigations 292
 
  • G.S. Gevorkyan, T.J. Hanks, A.H. Kachwala, S.S. Karkare, C.J. Knill, C.A. Sarabia Cardenas
    Arizona State University, Tempe, USA
 
  Funding: This work was supported by the U.S. National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams, and the DOE under Grant No. DE-SC0021092.
We present the first results of the commissioning of the 200 kV DC electron gun with a cryogenically cooled cathode at Arizona State University. The gun is specifically designed for studying a wide variety of novel cathode materials including single crystalline and epitaxially grown materials at 30 K temperatures to obtain the lowest possible intrinsic emittance of UED and XFEL applications [1]. We will present the measurements of the cryogenic performance of the gun and the first high voltage commissioning results.
[1] G. S. Gevorkyan et. al., Proc. of NAPAC19 MOPLM16 (2019)
 
slides icon Slides TUYD6 [12.632 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUYD6  
About • Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 29 September 2022
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TUPA19 Avoiding Combinatorial Explosion in Simulation of Multiple Magnet Errors in Swap-Out Safety Tracking for the Advanced Photon Source Upgrade 386
 
  • M. Borland, R. Soliday
    ANL, Lemont, Illinois, USA
 
  Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
The Advanced Photon Source (APS) is upgrading the storage ring to a hybrid seven-bend-achromat design with reverse bends, providing a natural emittance of 41 pm at 6 GeV. The small dynamic acceptance entails operation in on-axis swap-out mode. Careful consideration is required of the safety implications of injection with shutters open. Tracking studies require simulation of multiple simultaneous magnet errors, some combinations of which may introduce potentially dangerous conditions. A naive grid scan of possible errors, while potentially very complete, would be prohibitively time-consuming. We describe a different approach using biased sampling of particle distributions from successive scans. We also describe other aspects of the simulations, such as use of 3D field maps and a highly detailed aperture model.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA19  
About • Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 10 September 2022
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TUPA23 First Beam Results Using the 10-kW Harmonic Rf Solid-State Amplifier for the APS Particle Accumulator Ring 398
 
  • K.C. Harkay, T.G. Berenc, J.R. Calvey, J.C. Dooling, H. Shang, T.L. Smith, Y. Sun, U. Wienands
    ANL, Lemont, Illinois, USA
 
  Funding: Work supported by U. S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
The Advanced Photon Source (APS) particle accumulator ring (PAR) was designed to accumulate linac pulses into a single bunch using a fundamental radio frequency (rf) system, and longitudinally compress the beam using a harmonic rf system prior to injection into the booster. The APS Upgrade injectors will need to supply full-current bunch replacement with high single-bunch charge for swap-out injection in the new storage ring. Significant bunch lengthening is observed in the PAR at high charge, which negatively affects beam capture in the booster. Predictions showed that the bunch length could be compressed to better match the booster acceptance using a combination of higher beam energy and higher harmonic gap voltage. A new 10-kW harmonic rf solid-state amplifier (SSA) was installed in 2021 to raise the gap voltage and improve bunch compression. The SSA has been operating reliably. Initial results show that the charge-dependent bunch lengthening in PAR with higher gap voltage agrees qualitatively with predictions. A tool was written to automate bunch length data acquisition. Future plans to increase the beam energy, which makes the SSA more effective, will also be summarized.
 
poster icon Poster TUPA23 [2.477 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA23  
About • Received ※ 03 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 07 October 2022
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TUPA32 SCU Ends Configured as Phase Shifter 420
 
  • M.F. Qian
    ANL, Lemont, Illinois, USA
 
  Funding: Work supported by LDRD funding from Argonne National Laboratory, provided by the Director, Office of Science, of the U.S. DOE under Contract No. DE-AC02-06CH11357.
Dipole correctors and phase shifters are usually needed in the interspace of a permanent magnet (PM)-based undulator array for purposes of beam steering and phase matching when the field strength is changing. Unlike the PM-based undulators, the superconducting undulator (SCU) can change its end field with the help of varying currents in the end coils. By setting the end coil currents the beam-steering and the phase-matching could be realized, thus eliminating the need for standalone correctors and phase shifters, saving the interspace as well as reducing the mechanical complexity of an undulator array. We developed a procedure for determining the SCU end coil currents and verified it by numerical simulations. The procedure as well as the simulation results are described in this paper.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA32  
About • Received ※ 03 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 07 September 2022
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TUPA72 Comparison Study on First Bunch Compressor Schemes by Conventional and Double C-Chicane for MaRIE XFEL 496
 
  • H. Xu, P.M. Anisimov, L.D. Duffy, Q.R. Marksteiner
    LANL, Los Alamos, New Mexico, USA
 
  Funding: Laboratory Directed Research and Development program of Los Alamos National Laboratory, project number 20200287ER.
We report our comparison study on the first stage electron bunch compression schemes at 750 MeV using a conventional and a double C-chicane for the X-ray free electron laser (XFEL) under development for the Matter-Radiation Interactions in Extremes (MaRIE) initiative at Los Alamos National Laboratory. Compared to the performance of the conventional C-chicane bunch compressor, the double C-chicane scheme exhibits the capability of utilizing the transverse momentum shift induced by the coherent synchrotron radiation in the second C-chicane to compensate that generated in the first C-chicane, resulting in a compressed electron bunch with minimized transverse momentum shift along the beam. It is also found that the double C-chicane scheme can be designed to significantly better preserve the beam emittance in the course of the bunch compression. This is particularly beneficial for the MaRIE XFEL whose lasing performance critically depends on the preservation of the ultralow beam emittance.
 
poster icon Poster TUPA72 [1.339 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA72  
About • Received ※ 01 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 15 August 2022  
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TUPA80 Cyborg Beamline Development Updates 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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TUPA86 Simulations of Nanoblade Cathode Emissions with Image Charge Trapping for Yield and Brightness Analyses 535
 
  • J.I. Mann, G.E. Lawler, J.B. Rosenzweig, B. Wang
    UCLA, Los Angeles, California, USA
  • T. Arias, J.K. Nangoi
    Cornell University, Ithaca, New York, USA
  • S.S. Karkare
    Arizona State University, Tempe, USA
 
  Funding: National Science Foundation Grant No. PHY-1549132
Laser-induced field emission from nanostructures as a means to create high brightness electron beams has been a continually growing topic of study. Experiments using nanoblade emitters have achieved peak fields upwards of 40 GV/m according to semi-classical analyses, begging further theoretical investigation. A recent paper has provided analytical reductions of the common semi-infinite Jellium system for pulsed incident lasers. We utilize these results to further understand the physics underlying electron rescattering-type emissions. We numerically evaluate this analytical solution to efficiently produce spectra and yield curves. The effect of space-charge trapping at emission may be simply included by directly modifying these spectra. Additionally, we use a self-consistent 1-D time-dependent Schrödinger equation with an image charge potential to study the same system as a more exact, but computationally costly, approach. With these results we may finally investigate the mean transverse energy and beam brightness at the cathode in these extreme regimes.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-TUPA86  
About • Received ※ 02 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 03 September 2022
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WEPA01 Beam Dynamics Optimization of a Low Emittance Photoinjector Without Buncher Cavities 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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WEPA03 Status of the SLAC/MSU SRF Gun Development Project 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 icon 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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WEPA08 Design and Operation Experience of a Multi-Collimator/YAG Screen Device on LCLS II Low Energy Beamline 631
 
  • X. Liu, C. Adolphsen, M. Santana-Leitner, L. Xiao, F. Zhou
    SLAC, Menlo Park, California, USA
 
  During the commissioning of the normal conducting VHF RF gun of LCLS II, it was observed that field emission (dark current) of roughly 2 µA level was present under normal operation of the gun. While the dark current of this level is deemed manageable with existing beamline configurations, it is desired in precaution to add a collimator on the low energy beamline to block the dark current, being concerned that the dark current situation might worsen with time. Since no spare longitudinal space is available, the new device takes place of the existing YAG screen. The new device is made of a 15 mm thick copper plate, with four round apertures of 6, 8, 10, and 12 mm radius respectively. At the end of the collimator plate, features are made for clamping two YAG screens and mounting their corresponding mirrors for beam/halo profile imaging. The collimator plate is electrically insulated from the chamber so that it can also be used for measuring the dark current. A motor-driven UHV compatible linear translator shifts the device between positions. Besides design details, related thermal, beam dynamics, and radiation analyses as well as operation experience will be presented.

* Work supported by US DOE under contract AC02-76SF00515.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA08  
About • Received ※ 02 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 13 September 2022
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WEPA10 Determination of LCLS-II Gun-2 Prototype Dimensions 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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WEPA13 New Results at JLab Describing Operating Lifetime of GaAs Photo-guns 644
 
  • M.W. Bruker, J.M. Grames, C. Hernandez-Garcia, M. Poelker, S. Zhang
    JLab, Newport News, Virginia, USA
  • V.M. Lizárraga-Rubio, C.A. Valerio-Lizárraga
    ECFM-UAS, Culiacan, Sinaloa, Mexico
  • J.T. Yoskowitz
    ODU, Norfolk, Virginia, USA
 
  Funding: This work is supported by U.S. Department of Energy under DE-AC05-06OR23177 and by Consejo Nacional de Ciencia y Tecnología and the Universidad Autonoma de Sinaloa under PRO_A1_022.
Polarized electrons from GaAs photocathodes have been key to some of the highest-impact results of the Jefferson Lab science program over the past 30 years. During this time, various studies have given insight into improving the operational lifetime of these photocathodes in DC high-voltage photo-guns while using lasers with spatial Gaussian profiles of typically 0.5 mm to 1 mm FWHM, cathode voltages of 100 kV to 130 kV, and a wide range of beam currents up to multiple mA. In this contribution, we show recent experimental data from a 100 kV to 180 kV setup and describe our progress at predicting the lifetime based on the calculable dynamics of ionized gas molecules inside the gun. These new experimental studies at Jefferson Lab are specifically aimed at exploring the ion damage of higher-voltage guns being built for injectors.
 
poster icon Poster WEPA13 [1.644 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA13  
About • Received ※ 02 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 01 October 2022
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WEPA20 High-Gradient Wien Spin Rotators at Jefferson Lab 662
 
  • G.G. Palacios Serrano, P.A. Adderley, J.M. Grames, C. Hernandez-Garcia, M. Poelker
    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.
Nuclear physics experiments performed in the Contin-uous Electron Beam Accelerator Facility (CEBAF) at Jefferson Laboratory (JLab) require spin manipulation of electron beams. Two Wien spin rotators in the injector keV region are essential at CEBAF to establish longitudinal polarization at the end station target, and to flip the polarization direction by π rad to rule out false asymmetries. In a Wien filter, the homogeneous and independent electric and magnetic fields, along with the velocity vectors of the electrons that traverse it, form a mutually orthogonal system. The magnitude of the electrostatic field, established by biasing two highly-polished elec-trodes, defines the desired spin angle at the target yet deviates the beam trajectory due to the Lorentz force. The beam trajectory in the Wien is then re-established by adjusting the magnetic field, induced by an electromag-net encasing the device vacuum chamber. This contribu-tion describes the evolution design and high voltage testing of Wien filters for spin manipulation at increased beam energies in the keV injector region, required by high precision parity violation experiments like MOLLER.
 
poster icon Poster WEPA20 [1.434 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA20  
About • Received ※ 02 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 05 September 2022
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WEPA22 Measuring the Electric Dipole Moment of the Electron in a Two-Energy Spin-Transparent Storage Ring 665
 
  • R. Suleiman, Y.S. Derbenev
    JLab, Newport News, Virginia, USA
  • V.S. Morozov
    ORNL RAD, Oak Ridge, Tennessee, USA
 
  Funding: This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 and by UT-Battelle, LLC, under contract DE-AC05-00OR22725.
We will present a new design of a two-energy storage ring for low energy (0.2 to 2 MeV) polarized electron bunches [1]. The new design is based on the transparent spin methodology that cancels the spin precession due to the magnetic dipole moment at any energy while allowing for spin precession induced by the fundamental physics of interest to accumulate. The buildup of the vertical component of beam polarization can be measured using standard Mott polarimetry that is optimal at low electron energy. These rings can be used to measure the permanent electric dipole moment of the electron, relevant to CP violation and matter-antimatter asymmetry in the universe, and to search for dark energy and ultra-light dark matter.
[1] R. Suleiman, V.S. Morozov, and Y.S. Derbenev, On possibilities of high precision experiments in fundamental physics in storage rings of low energy polarized electron beams, arXiv:2105.11575 (2021)
 
poster icon Poster WEPA22 [0.781 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA22  
About • Received ※ 04 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 07 October 2022
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WEPA25 Field Emission Mitigation in CEBAF SRF Cavities Using Deep Learning 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 icon 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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WEPA62 Design and Commissioning of the ASU CXLS RF System 764
 
  • B.J. Cook, G.I. Babic, J.R.S. Falconer, W.S. Graves, M.R. Holl, S.P. Jachim, R.E. Larsen
    Arizona State University, Tempe, USA
 
  Funding: This work was supported in part by NSF award #1935994.
The Compact X-ray Light Source (CXLS) uses inverse Compton scattering of a high intensity laser off a bright, relativistic electron beam to produce hard x-rays. The accelerator consists of a photoinjector and three standing-wave linac sections, which are powered by two 6-MW klystrons operating at 9.3 GHz with a repetition rate of 1 kHz. This paper presents the design and commissioning of the CXLS RF systems consisting of both high-power RF structures and low-power diagnostics. The high-power RF system is comprised of two solid state amplifier and klystron modulator sets, various directional couplers, and three phase shifter power dividers. The low-level system consists of a master oscillator and laser phase lock, IQ modulators, IQ demodulators, and downconverters. We present measurements of the low-level and high-power RF phase and amplitude stability showing RMS timing jitter in the tens of femtoseconds and amplitude jitter below 0.1% at high power.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA62  
About • Received ※ 29 July 2022 — Revised ※ 03 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 19 August 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WEPA65 On-Chip Photonics Integrated Photocathodes 773
 
  • A.H. Kachwala, O. Chubenko, S.S. Karkare
    Arizona State University, Tempe, USA
  • R. Ahsan
    USC, Los Angeles, California, USA
  • H.U. Chae, R. Kapadia
    University of Southern California, Los Angeles, California, USA
 
  Funding: This work is supported by the NSF Center for Bright Beams under award PHY-1549132, and by the Department of Energy, Office of Science under awards DE-SC0021092, and DE-SC0021213.
Photonics integrated photocathodes can result in advanced electron sources for various accelerator applications. In such photocathodes, light can be directed using waveguides and other photonic components on the substrate underneath a photoemissive film to generate electron emission from specific locations at sub-micron scales and at specific times at 100-femtosecond scales along with triggering novel photoemission mechanisms resulting in brighter electron beams and enabling unprecedented spatio-temporal shaping of the emitted electrons. In this work we have demonstrated photoemission confined in the transverse direction using a nanofabricated Si3N4 waveguide underneath a 40-nm thick cesiated GaAs photoemissive film, thus demonstrating a proof of principle feasibility of such photonics integrated photocathodes. This work paves the way to integrate the advances in the field of photonics and nanofabrication with photocathodes to develop better electron sources.
 
poster icon Poster WEPA65 [0.642 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA65  
About • Received ※ 26 July 2022 — Revised ※ 06 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 10 August 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WEPA66 Near-Threshold Photoemission from Graphene Coated Cu Single Crystals 776
 
  • C.J. Knill, S.S. Karkare
    Arizona State University, Tempe, USA
  • H. Ago, K. Kawahara
    Global Innovation Center, Kyushu University, Kasuga, Fukuoka, Japan
  • E. Batista, N.A. Moody, G.X. Wang, H. Yamaguchi, P. Yang
    LANL, Los Alamos, New Mexico, USA
 
  Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams, and by the Department of Energy under Grant DE-SC0021092.
The brightness of electron beams emitted from photocathodes plays a key role in the performance of x-ray free electron lasers (XFELs) and ultrafast electron diffraction (UED) experiments. In order to achieve the maximum beam brightness, the electrons need to be emitted from photocathodes with the smallest possible mean transverse energy (MTE). Recent studies have looked at the effect that a graphene coating has on the quantum efficiency (QE) of the cathode [1]. However, there have not yet been any investigations into the effect that a graphene coating has on the MTE. Here we report on MTE and QE measurements of a graphene coated Cu(110) single crystal cathode at room and cryogenic temperatures. At room temperature, a minimum MTE of 25 meV was measured at 295 nm. This MTE remained stable at 25 meV over several days. At 77 K, the minimum MTE of 9 meV was measured at 290 nm. We perform density functional theory (DFT) calculations to look at the effects of a graphene coating on a Cu(111) surface state. These calculations show that the graphene coating reduces the radius of the surface state, allowing for emission from a lower transverse energy state in comparison to bare Cu(111).
[1] F. Liu et al, Appl. Phys. Lett. 110, 041607 (2017); https://doi.org/10.1063/1.4974738
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA66  
About • Received ※ 28 July 2022 — Revised ※ 19 July 2022 — Accepted ※ 07 August 2022 — Issue date ※ 10 August 2022
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WEPA68 Record Quantum Efficiency from Superlattice Photocathode for Spin Polarized Electron Beam Production 784
 
  • J.P. Biswas, L. Cultrera, K. Kisslinger, W. Liu, J. Skarita, E. Wang
    BNL, Upton, New York, USA
  • S.D. Hawkins, J.F. Klem, S.R. Lee
    Sandia National Laboratories, Albuquerque, New Mexico, USA
 
  Funding: The work is supported by Brookhaven Science Associates, LLC under Contract DESC0012704 with the U.S. DOE. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
Electron sources producing highly spin-polarized electron beams are currently possible only with photocathodes based on GaAs and other III-V semiconductors. GaAs/GaAsP superlattice (SL) photocathodes with a distributed Bragg reflector (DBR) represent the state of the art for the production of spin-polarized electrons. We present results on a SL-DBR GaAs/GaAsP structure designed to leverage strain compensation to achieve simultaneously high QE and spin polarization. These photocathode structures were grown using molecular beam epitaxy and achieved quantum efficiencies exceeding 15% and electron spin polarization of about 75% when illuminated with near bandgap photon energies.
 
poster icon Poster WEPA68 [4.506 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA68  
About • Received ※ 20 July 2022 — Revised ※ 02 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 10 August 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WEPA76 Radio Frequency System of the NSLS-II Injector LINAC for Multi-Bunch-Mode Beams 813
 
  • H. Ma, J. Rose, C. Sorrentino
    BNL, Upton, New York, USA
 
  Funding: US DOE, Office of BES
The Multi-Bunch Mode (MBM) beam injection opera-tion of NSLS-II LINAC requires a beam-loading compen-sation for its rf field. That requirement has a significant impact on its radio frequency system (RF), in both the low-level rf control and the high-power klystron transmit-ters. Specifically, for the rf control, it requires the output vector modulation have enough bandwidth to be able to respond the transients by the MBM beam of 40~300 nS long. For the high-power rf transmitters, it requires the klystrons to operate in a near-linear region to be able to respond the linear rf control for the beam-loading compensation, which means a need of ~30% extra rf power overhead, compared to the single-bunch mode operations. The digital signal processing and the network configuration for the rf controllers are also the important areas in the implementation. The original system design was driven by the MBM beam operation requirements, and our system upgrade today continues to be guided by the same principles.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA76  
About • Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 10 August 2022 — Issue date ※ 24 August 2022
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WEPA81 Time-Resolved Experiments at NSLS II: Motivation and Machine Capabilities 826
 
  • G.M. Wang, B. Bacha, G. Bassi, G.L. Carr, Y. Hidaka, Y. Hu, Y. Li, C. Mazzoli, D. Padrazo Jr, R.S. Rainer, J. Rose, J.T. Sadowski, V.V. Smaluk, Y. Tian, L. Wiegart, G. Williams, X. Yang
    BNL, Upton, New York, USA
 
  NSLS-II is a 3-GeV third-generation synchrotron light source at Brookhaven National Lab. The storage ring has been in routine operations for over six years and hosts 28 operating beamlines. The storage ring performance has continuously improved, including 500-mA with limited insertion devices closed, and routine 400-mA top off operation with 90% uniform filling pattern. Recently, we are exploring different operation modes, uniform multi single-bunch mode, and camshaft mode with a high single-bunch charge, to support timing-resolved user experiments. In this paper, we explore the potential for scientific experiments using the pulsed nature of the NSLS, summarize the user requirements on the beam parameters and the progress of accelerator studies.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA81  
About • Received ※ 04 August 2022 — Revised ※ 12 August 2022 — Accepted ※ 13 August 2022 — Issue date ※ 22 August 2022
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THYD1 XFEL as a Low-Emittance Injector for a 4th-Generation Synchrotron Radiation Source 850
 
  • T. Hara
    RIKEN SPring-8 Center, Hyogo, Japan
 
  Low-emittance beam injection is required for the future SPring-8-II due to its small injection beam aperture. To meet this requirement, the SACLA linac has been used as a low-emittance injector since 2020 [1]. In order to perform the beam injection in parallel with XFEL operation, three accelerators are virtually constructed in a control system for the two XFEL beamlines and the beam injection, and thus the accelerator parameters can be independently tuned. Since the reference clock frequencies of the two accelerators are not related by an integer multiple, a new timing system was developed that achieves 3.8 ps (rms) synchronization. To maintain bunch purity better than 1e-8, which is routinely requested at SPring-8, an electron sweeper and an RF knock-out system are introduced for the SACLA injector and the SPring-8 storage ring. Although 0.1 nm-rad emittance of SACLA is increased by an order of magnitude at a transport line mainly due to quantum excitation of synchrotron radiation, it is still small enough for SPring-8-II. By shutting down an old dedicated injector complex, energy consumption has been significantly reduced, and it contributes to create a low-carbon society.
The speaker present this work on behalf of RIKEN-JASRI project team.
[1] Toru Hara et al., Phys. Rev. Accel. Beams 24, 110702 (2021).
 
slides icon Slides THYD1 [10.103 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYD1  
About • Received ※ 29 July 2022 — Revised ※ 05 August 2022 — Accepted ※ 07 August 2022 — Issue date ※ 23 September 2022
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THYD2
The Challenging Physics Regimes of High Current Electron Beams  
 
  • J.E. Coleman
    LANL, Los Alamos, New Mexico, USA
 
  Electrons with intense space charge produce truly challenging physics regimes every step of the way. Hollow electron beams produced in the injector with thin enhanced edges are subject to the diocotron instability or a velocity shear, which is related to the Kelvin Helmholtz instability. Misaligned focusing elements and non-uniform current densities lead to non-linear transport effects in accelerator transport. Electrons focused to intensities >105 J/cm2 or ne ~ 1019 m-3 can produce hot, Te > 1 eV, solid density plasmas that expand slowly over several hundred nanoseconds. The subsequent temperature and density gradients that are produced can generate magnetic fields. Example measurements and calculations of each of these phenomena are presented.  
slides icon Slides THYD2 [7.608 MB]  
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THYD3 Update on the Status of C-Band Research and Facilities at LANL 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 icon Slides THYD3 [3.331 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYD3  
About • Received ※ 31 July 2022 — Revised ※ 08 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 04 October 2022
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THYD4 Progress on the APS-U Injector Upgrade 859
 
  • J.R. Calvey, T. Fors, K.C. Harkay, U. Wienands
    ANL, Lemont, Illinois, USA
 
  Funding: Work supported by U. S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
For the APS-Upgrade, it was decided to leave the present APS injector chain in place and make individual improvements where needed. The main challenges faced by the injectors are delivering a high charge bunch (up to 16 nC in a single shot) to the storage ring, operating the booster synchrotron and storage ring at different rf frequencies, and maintaining good charge stability during APS-U operations. This paper will summarize recent progress on the injector upgrade. Topics include bucket targeting with the new injection/extraction timing system (IETS), modeling of high charge longitudinal instability in the PAR, and measurements of charge stability for different modes of operation.
 
slides icon Slides THYD4 [2.015 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYD4  
About • Received ※ 19 July 2022 — Accepted ※ 11 August 2022 — Issue date ※ 22 August 2022  
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THYD5 Development of Nanopatterned Strong Field Emission Cathodes 863
 
  • G.E. Lawler, N. Majernik, J.I. Mann, N. Montanez, J.B. Rosenzweig
    UCLA, Los Angeles, California, USA
 
  Funding: This work was supported by the Center for Bright Beams, National Science Foundation Grant No. PHY-1549132 and DOE HEP Grant DE-SC0009914.
Increasing brightness at the cathode is highly desirable for a diverse suite of applications in the electron accelerator community. These applications range from free electron lasers to ultrafast electron diffraction. Many options for higher brightness cathodes are under investigation notably semiconductor cathodes. We consider here the possibility for an alternative paradigm whereby the cathode surface is controlled to reduce the effective area of illumination and emission. We fabricated nanoblade metallic coated cathodes using common nanofabrication techniques. We have demonstrated that a beam can be successfully extracted with a low emittance and we have reconstructed a portion of the energy spectrum. As a result of our particular geometry, our beam possesses a notably high aspect ratio in its transverse plane. We can now begin to consider modifications for the production of intentionally patterned beams such as higher aspect ratios and hollow beams.
 
slides icon Slides THYD5 [4.652 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYD5  
About • Received ※ 02 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 05 October 2022  
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THYD6 Arrival Time and Energy Jitter Effects on the Performance of X-Ray Free Electron Laser Oscillator 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 icon Slides THYD6 [1.935 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYD6  
About • Received ※ 01 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 06 August 2022 — Issue date ※ 03 October 2022
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