NAPAC2022 - List of Keywords (HOM)

Paper	Title	Other Keywords	Page
MOYE5	In Situ Plasma Processing of Superconducting Cavities at JLab	cavity, plasma, cryomodule, 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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPA12	Commissioning of HOM Detectors in the First Cryomodule of the LCLS-II Linac	cavity, 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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPA91	Plasma Processing of Superconducting Quarter-Wave Resonators Using a Higher-Order Mode	plasma, cavity, SRF, cryomodule	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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPA27	Longitudinal Feedback Dynamics in Storage Rings with Small Synchrotron Tunes	feedback, simulation, synchrotron, cavity	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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPA09	A Parallel Automatic Simulation Tool for Cavity Shape Optimization	cavity, 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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPA26	197 MHz Waveguide Loaded Crabbing Cavity Design for the Electron-Ion Collider	cavity, 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
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Other Keywords

Page

MOYE5

In Situ Plasma Processing of Superconducting Cavities at JLab

cavity, plasma, cryomodule, 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

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPA12

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

cavity, 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

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPA91

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

plasma, cavity, SRF, cryomodule

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

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPA27

Longitudinal Feedback Dynamics in Storage Rings with Small Synchrotron Tunes

feedback, simulation, synchrotron, cavity

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

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPA09

A Parallel Automatic Simulation Tool for Cavity Shape Optimization

cavity, 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

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPA26

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

cavity, 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

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)