IPAC2018 - List of Keywords (multipactoring)

Paper	Title	Other Keywords	Page
TUZGBE3	Towards Implementation of Laser Engineered Surface Structures for Electron Cloud Mitigation	electron, laser, vacuum, operation	1220
	M. Sitko, V. Baglin, S. Calatroni, P. Chiggiato, B. Di Girolamo, E. Garcia-Tabares Valdivieso, M. Taborelli CERN, Geneva, Switzerland A. Abdolvand, D. Bajek, S. Wackerow University of Dundee, Nethergate, Dundee, Scotland, United Kingdom M. Colling, T.J. Jones, P.A. McIntosh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	The LHC operation has proven that the electron cloud could be a significant limiting factor in machine performance, in particular for future High Luminosity LHC (HL-LHC) beams. Electron clouds, generated by electron multipacting in the beam pipes, leads to beam instabilities and beam-induced heat load in cryogenic systems. Laser Engineered Surface Structures (LESS) is a novel surface treatment which changes the morphology of the internal surfaces of vacuum chambers. The surface modification results in a reduced secondary electron yield (SEY) and, consequently, in the eradication of the electron multipacting. Low SEY values of the treated surfaces and flexibility in choosing the laser parameters make LESS a promising treatment for future accelerators. LESS can be applied both in new and existing accelerators owing to the possibility of automated in-situ treatment. This approach has been developed and optimised for the LHC beam screens in which the electron cloud has to be mitigated before the HL-LHC upgrade. We will present the latest steps towards the implementation of LESS.
	Slides TUZGBE3 [1.825 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUZGBE3
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WEPMF044	Updates on the DC Field Dependence Cavity	cavity, niobium, SRF, simulation	2465
	J.T. Maniscalco, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Work at Cornell has demonstrated good agreement between a theoretical model by A. Gurevich of the anti-Q-slope (a field-dependent decrease of the microwave surface resistance) and experimental results from impurity-doped niobium. As a corollary, the model predicts that a strong DC magnetic field applied parallel to the RF surface will produce a similar decrease in surface resistance. In order to explore this prediction for many materials, we have designed a new coaxial cavity with a strong, uniform DC field superimposed over a weak RF field on a removable and replaceable niobium sample. Here we present updates on the progress of this new cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF044
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WEPMF045	Performance of the Prototype SRF Half-Wave-Resonators Tested at Cornell for the RAON Project	cavity, SRF, pick-up, radiation	2468
	M. Ge, F. Furuta, T. Gruber, S.W. Hartman, M. Liepe, J.T. Maniscalco, T.I. O'Connell, P.J. Pamel, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA B.H. Choi, J. Joo, J.W. Kim, W.K. Kim, J. Lee, I. Shin IBS, Daejeon, Republic of Korea
	Two prototype superconducting half-wave-resonator (162.5 MHz and β=0.12) for the RAON project have been successfully tested at Cornell University. Detailed vertical performance testing included (1) test of the bare cavity without the helium tank, and (2) test of the dressed cavity with a helium tank. In this paper, we report on the development of the test infrastructure, test results, and performance data analysis, showing that the specifications for RAON were met.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF045
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WEPMF051	Multipacting in an RF Window: Simulations and Measurements	electron, simulation, resonance, gun	2483
	M. Bousonville, S. Choroba DESY, Hamburg, Germany
	Electron guns are used in the accelerators of the European XFEL and FLASH. They are operated at 1.3 GHz. The RF peak power is 5 MW at 650 us pulse width and 10 Hz repetition rate. In order to understand the multipacting that occurs during conditioning, it was simulated in the RF window type that is used for the electron gun in the XFEL. The reduction in secondary emission yield associated with conditioning was taken into account. Since the RF windows are tested with high power on a test stand before their use, without the electron gun, measurement results are available which are compared with the simulation results. The main advantage of the simulation compared to the measurement is that the locations of multipacting can be determined in the RF window. This could be helpful for the development of high-power RF components in the future, in order to detect pronounced multipacting resonances even before production and to avoid them by design changes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF051
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WEPMG005	First Beam Test of Laser Engineered Surface Structures (LESS) at Cryogenic Temperature in CERN SPS Accelerator	electron, laser, vacuum, cryogenics	2616
	R. Salemme, V. Baglin, S. Calatroni, P. Chiggiato, B. Di Girolamo, E. Garcia-Tabares Valdivieso, B. Jenninger, L. Prever-Loiri, M. Sitko CERN, Geneva, Switzerland A. Abdolvand, S. Wackerow University of Dundee, Nethergate, Dundee, Scotland, United Kingdom R. Salemme ITER Organization, St. Paul lez Durance, France
	Electron cloud mitigation is an essential requirement for accelerators of positive particles with high intensity beams to guarantee beam stability and limited heat load in cryogenic systems. Laser Engineered Surface Structures (LESS) are being considered, within the High Luminosity upgrade of the LHC collider at CERN (HL-LHC), as an option to reduce the Secondary Electron Yield (SEY) of the surfaces facing the beam, thus suppressing the elec-tron cloud phenomenon. As part of this study, a 2.2 m long Beam Screen (BS) with LESS has been tested at cryogenic temperature in the COLD bore EXperiment (COLDEX) facility in the SPS accelerator at CERN. In this paper, we describe the manufacturing procedure of the beam screen, the employed laser treatment technique and discuss our first observations in COLDEX confirming electron cloud suppression.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMG005
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WEPML015	Preparation and Qualification of Jacketed SSR1 Cavities for String Assembly at Fermilab	cavity, vacuum, cryomodule, controls	2714
	D. Passarelli, P. Berrutti, S.K. Chandrasekaran, J.P. Ozelis, M. Parise, L. Ristori, A.M. Rowe, A.I. Sukhanov Fermilab, Batavia, Illinois, USA
	The qualification of dressed 325 MHz Single Spoke Resonators type 1 (SSR1) to meet technical requirements is an important milestone in the development of the SSR1 cryomodule for the PIP-II Project at Fermilab. This paper reports the procedures and lessons learned in processing and preparing these cavities for horizontal cold testing prior to integration into a cavity string assembly.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML015
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WEPML046	Multipactor Discharge in Superconducting Accelerating CH Cavities	electron, cavity, linac, heavy-ion	2800
	M. Gusarova, D. I. Kiselev MEPhI, Moscow, Russia F.D. Dziuba, T. Kürzeder, M. Miski-Oglu HIM, Mainz, Germany M. Gusarova JINR, Dubna, Moscow Region, Russia
	The results of numerical simulations of multipacting discharge in a superconducting accelerating CH cavity are presented in this paper. The localization of multipactor trajectories in the 15-gap 217 MHz superconducting (sc) CH cavity at various levels of accelerating voltage is considered.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML046
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THPAL033	Measurement of the Internal Dark Current in a High Gradient Accelerator Structure at 17 GHz	acceleration, electron, experiment, simulation	3705
	H. Xu, M.A. Shapiro, R.J. Temkin MIT/PSFC, Cambridge, Massachusetts, USA
	Funding: Work supported by the U.S. Department of Energy, Office of High Energy Physics, under Grant No. DE-SC0015566 We report a study of internal dark current generation by multipactor inside a 17 GHz single cell standing wave disk-loaded waveguide accelerator structure. The multipactor takes place on the side wall of the central cell, driven by the local rf electric and magnetic fields. Theory indicates that a resonant multipactor mode with two rf cycles can be excited near 45 MV/m gradient and a single rf cycle multipactor mode near 60 MV/m. The accelerator structure had two thin slits opened on the side wall of the central cell to directly extract and measure the internal dark current. The dark current was measured as a function of the gradient up to a gradient of 70 MV/m. The experimental results agreed well with theory, showing the two predicted multipactor modes. To further study the effect of the central cell side wall surface properties on the structure performance, we prepared and tested a second structure with the central cell side wall coated with a layer of diamond-like carbon. The comparison of the results showed that the coating reduced the internal dark current and thus enhanced the structure performance considerably.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL033
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THPAL085	High Power RF Conditioning on CLARA	cavity, vacuum, linac, solenoid	3852
	L.S. Cowie, D.J. Scott STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G. Burt, W.L. Millar Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
	The CLARA accelerator at Daresbury Laboratory will have 8 normal conducting RF cavities. Automating the high power RF conditioning of these cavities will mean a repeatable, research-lead process is followed. An auto-mated algorithm has been written in Python. A prototype algorithm was used to condition the first CLARA travel-ling wave linac in October 2017. The linac was success-fully conditioned over approximately 12 million pulses up to 27 MW for a 750 ns pulse. A more complex and robust algorithm was used to re-condition the standing wave 10 Hz photoinjector after a cathode change. The photoinjec-tor was conditioned to 10 MW for a 2.5 μs pulse in Feb-ruary 2018 over 2.1 million pulses. Conditioning method; differences for travelling and standing wave structures; difficulties and interesting phenomena are all discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL085
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THPAL110	High-Power RF Test of Coaxial Couplers for the Injection Linac of XiPAF	cavity, vacuum, coupling, linac	3899
	Y. Lei, X. Guan, R. Tang, X.W. Wang, Q.Z. Xing, H.Y. Zhang, S.X. Zheng TUB, Beijing, People's Republic of China J. Jiang, H. Li, C. Yu Beijing Aerospace Guagntong Technology Co., Beijing, People's Republic of China
	For the high-power RF test of the coaxial couplers which will be employed on the linac injector of the XiPAF (Xi'an Proton Application Facility) project, a high-power conditioning cavity was designed and manufactured [1]. There are some optimized aspects on the cavity and couplers to obtain better RF performance during the high-power testing process. The traveling-wave test and full-power-reflection test were executed to check whether the coupler can afford the enough power level for the linac operation, and whether only one coupler can afford the total power for the RFQ. The construction of the testing stand, optimization of RF parameters and results of high-power RF test are presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL110
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THPAL123	Fabrication and Test of β=0.3 325MHz Balloon Single Spoke Resonator	cavity, niobium, linac, TRIUMF	3934
	Z.Y. Yao, J.J. Keir, D. Kishi, D. Lang, R.E. Laxdal, H.L. Liu, Y. Ma, B. Matheson, B.S. Waraich, Q. Zheng, V. Zvyagintsev TRIUMF, Vancouver, Canada
	A novel balloon variant of the single spoke resonator (SSR) has been designed, fabricated and tested at TRIUMF. The cavity is the β=0.3 325 MHz SSR1 prototype for the Rare Isotope Science Project (RISP) in Korea. The balloon variant is specifically designed to reduce the likelihood of multipacting barriers near the operating point. A systematic multipacting study led to a novel geometry, a spherical cavity with re-entrant irises plus a spoke. The balloon cavity provides competitive RF parameters and a robust mechanical structure. Cold tests demonstrated the principle of the balloon concept. The fabrication experience and the preliminary test results will be reported in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL123
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THPML015	Dielectric Multipactor Discharges at 110 GHz	cavity, experiment, GUI, vacuum	4684
	S. C. Schaub MIT, Cambridge, Massachusetts, USA M.A. Shapiro, R.J. Temkin MIT/PSFC, Cambridge, Massachusetts, USA
	A 1.5 MW, 110 GHz gyrotron has been used to experimentally measure the maximum sustainable fields on dielectric materials in vacuum. The purpose of this work is to evaluate the suitability of these materials for future applications in high frequency linear accelerators and high power terahertz components. To our knowledge, these are the first measurements of multipactor phenomena in the millimeter wave or terahertz frequency range. Materials tested include alumina, sapphire, fused quartz, crystal quartz, and high resistivity silicon. Dielectric samples were tested both as windows, with electric fields parallel to the surface, and sub-wavelength dielectric rod waveguides, with electric fields perpendicular to the surface. Surface electric fields in excess of 52 MV/m were achieved in 3 microsecond pulses. Visible light emission, absorbed/scattered microwave power, and emitted electrons were measured to characterize the discharges on the dielectric surfaces. The results of these experiments have been compared to theoretical calculations of multipactor discharges, testing these theories at significantly higher frequencies than has been done before.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML015
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Paper

Title

Other Keywords

Page

TUZGBE3

Towards Implementation of Laser Engineered Surface Structures for Electron Cloud Mitigation

electron, laser, vacuum, operation

1220

M. Sitko, V. Baglin, S. Calatroni, P. Chiggiato, B. Di Girolamo, E. Garcia-Tabares Valdivieso, M. Taborelli
CERN, Geneva, Switzerland
A. Abdolvand, D. Bajek, S. Wackerow
University of Dundee, Nethergate, Dundee, Scotland, United Kingdom
M. Colling, T.J. Jones, P.A. McIntosh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

The LHC operation has proven that the electron cloud could be a significant limiting factor in machine performance, in particular for future High Luminosity LHC (HL-LHC) beams. Electron clouds, generated by electron multipacting in the beam pipes, leads to beam instabilities and beam-induced heat load in cryogenic systems. Laser Engineered Surface Structures (LESS) is a novel surface treatment which changes the morphology of the internal surfaces of vacuum chambers. The surface modification results in a reduced secondary electron yield (SEY) and, consequently, in the eradication of the electron multipacting. Low SEY values of the treated surfaces and flexibility in choosing the laser parameters make LESS a promising treatment for future accelerators. LESS can be applied both in new and existing accelerators owing to the possibility of automated in-situ treatment. This approach has been developed and optimised for the LHC beam screens in which the electron cloud has to be mitigated before the HL-LHC upgrade. We will present the latest steps towards the implementation of LESS.

Slides TUZGBE3 [1.825 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUZGBE3

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WEPMF044

Updates on the DC Field Dependence Cavity

cavity, niobium, SRF, simulation

2465

J.T. Maniscalco, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Work at Cornell has demonstrated good agreement between a theoretical model by A. Gurevich of the anti-Q-slope (a field-dependent decrease of the microwave surface resistance) and experimental results from impurity-doped niobium. As a corollary, the model predicts that a strong DC magnetic field applied parallel to the RF surface will produce a similar decrease in surface resistance. In order to explore this prediction for many materials, we have designed a new coaxial cavity with a strong, uniform DC field superimposed over a weak RF field on a removable and replaceable niobium sample. Here we present updates on the progress of this new cavity.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF044

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WEPMF045

Performance of the Prototype SRF Half-Wave-Resonators Tested at Cornell for the RAON Project

cavity, SRF, pick-up, radiation

2468

M. Ge, F. Furuta, T. Gruber, S.W. Hartman, M. Liepe, J.T. Maniscalco, T.I. O'Connell, P.J. Pamel, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
B.H. Choi, J. Joo, J.W. Kim, W.K. Kim, J. Lee, I. Shin
IBS, Daejeon, Republic of Korea

Two prototype superconducting half-wave-resonator (162.5 MHz and β=0.12) for the RAON project have been successfully tested at Cornell University. Detailed vertical performance testing included (1) test of the bare cavity without the helium tank, and (2) test of the dressed cavity with a helium tank. In this paper, we report on the development of the test infrastructure, test results, and performance data analysis, showing that the specifications for RAON were met.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF045

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WEPMF051

Multipacting in an RF Window: Simulations and Measurements

electron, simulation, resonance, gun

2483

M. Bousonville, S. Choroba
DESY, Hamburg, Germany

Electron guns are used in the accelerators of the European XFEL and FLASH. They are operated at 1.3 GHz. The RF peak power is 5 MW at 650 us pulse width and 10 Hz repetition rate. In order to understand the multipacting that occurs during conditioning, it was simulated in the RF window type that is used for the electron gun in the XFEL. The reduction in secondary emission yield associated with conditioning was taken into account. Since the RF windows are tested with high power on a test stand before their use, without the electron gun, measurement results are available which are compared with the simulation results. The main advantage of the simulation compared to the measurement is that the locations of multipacting can be determined in the RF window. This could be helpful for the development of high-power RF components in the future, in order to detect pronounced multipacting resonances even before production and to avoid them by design changes.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF051

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WEPMG005

First Beam Test of Laser Engineered Surface Structures (LESS) at Cryogenic Temperature in CERN SPS Accelerator

electron, laser, vacuum, cryogenics

2616

R. Salemme, V. Baglin, S. Calatroni, P. Chiggiato, B. Di Girolamo, E. Garcia-Tabares Valdivieso, B. Jenninger, L. Prever-Loiri, M. Sitko
CERN, Geneva, Switzerland
A. Abdolvand, S. Wackerow
University of Dundee, Nethergate, Dundee, Scotland, United Kingdom
R. Salemme
ITER Organization, St. Paul lez Durance, France

Electron cloud mitigation is an essential requirement for accelerators of positive particles with high intensity beams to guarantee beam stability and limited heat load in cryogenic systems. Laser Engineered Surface Structures (LESS) are being considered, within the High Luminosity upgrade of the LHC collider at CERN (HL-LHC), as an option to reduce the Secondary Electron Yield (SEY) of the surfaces facing the beam, thus suppressing the elec-tron cloud phenomenon. As part of this study, a 2.2 m long Beam Screen (BS) with LESS has been tested at cryogenic temperature in the COLD bore EXperiment (COLDEX) facility in the SPS accelerator at CERN. In this paper, we describe the manufacturing procedure of the beam screen, the employed laser treatment technique and discuss our first observations in COLDEX confirming electron cloud suppression.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMG005

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WEPML015

Preparation and Qualification of Jacketed SSR1 Cavities for String Assembly at Fermilab

cavity, vacuum, cryomodule, controls

2714

D. Passarelli, P. Berrutti, S.K. Chandrasekaran, J.P. Ozelis, M. Parise, L. Ristori, A.M. Rowe, A.I. Sukhanov
Fermilab, Batavia, Illinois, USA

The qualification of dressed 325 MHz Single Spoke Resonators type 1 (SSR1) to meet technical requirements is an important milestone in the development of the SSR1 cryomodule for the PIP-II Project at Fermilab. This paper reports the procedures and lessons learned in processing and preparing these cavities for horizontal cold testing prior to integration into a cavity string assembly.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML015

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WEPML046

Multipactor Discharge in Superconducting Accelerating CH Cavities

electron, cavity, linac, heavy-ion

2800

M. Gusarova, D. I. Kiselev
MEPhI, Moscow, Russia
F.D. Dziuba, T. Kürzeder, M. Miski-Oglu
HIM, Mainz, Germany
M. Gusarova
JINR, Dubna, Moscow Region, Russia

The results of numerical simulations of multipacting discharge in a superconducting accelerating CH cavity are presented in this paper. The localization of multipactor trajectories in the 15-gap 217 MHz superconducting (sc) CH cavity at various levels of accelerating voltage is considered.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML046

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THPAL033

Measurement of the Internal Dark Current in a High Gradient Accelerator Structure at 17 GHz

acceleration, electron, experiment, simulation

3705

H. Xu, M.A. Shapiro, R.J. Temkin
MIT/PSFC, Cambridge, Massachusetts, USA

Funding: Work supported by the U.S. Department of Energy, Office of High Energy Physics, under Grant No. DE-SC0015566
We report a study of internal dark current generation by multipactor inside a 17 GHz single cell standing wave disk-loaded waveguide accelerator structure. The multipactor takes place on the side wall of the central cell, driven by the local rf electric and magnetic fields. Theory indicates that a resonant multipactor mode with two rf cycles can be excited near 45 MV/m gradient and a single rf cycle multipactor mode near 60 MV/m. The accelerator structure had two thin slits opened on the side wall of the central cell to directly extract and measure the internal dark current. The dark current was measured as a function of the gradient up to a gradient of 70 MV/m. The experimental results agreed well with theory, showing the two predicted multipactor modes. To further study the effect of the central cell side wall surface properties on the structure performance, we prepared and tested a second structure with the central cell side wall coated with a layer of diamond-like carbon. The comparison of the results showed that the coating reduced the internal dark current and thus enhanced the structure performance considerably.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL033

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THPAL085

High Power RF Conditioning on CLARA

cavity, vacuum, linac, solenoid

3852

L.S. Cowie, D.J. Scott
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
G. Burt, W.L. Millar
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom

The CLARA accelerator at Daresbury Laboratory will have 8 normal conducting RF cavities. Automating the high power RF conditioning of these cavities will mean a repeatable, research-lead process is followed. An auto-mated algorithm has been written in Python. A prototype algorithm was used to condition the first CLARA travel-ling wave linac in October 2017. The linac was success-fully conditioned over approximately 12 million pulses up to 27 MW for a 750 ns pulse. A more complex and robust algorithm was used to re-condition the standing wave 10 Hz photoinjector after a cathode change. The photoinjec-tor was conditioned to 10 MW for a 2.5 μs pulse in Feb-ruary 2018 over 2.1 million pulses. Conditioning method; differences for travelling and standing wave structures; difficulties and interesting phenomena are all discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL085

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THPAL110

High-Power RF Test of Coaxial Couplers for the Injection Linac of XiPAF

cavity, vacuum, coupling, linac

3899

Y. Lei, X. Guan, R. Tang, X.W. Wang, Q.Z. Xing, H.Y. Zhang, S.X. Zheng
TUB, Beijing, People's Republic of China
J. Jiang, H. Li, C. Yu
Beijing Aerospace Guagntong Technology Co., Beijing, People's Republic of China

For the high-power RF test of the coaxial couplers which will be employed on the linac injector of the XiPAF (Xi'an Proton Application Facility) project, a high-power conditioning cavity was designed and manufactured [1]. There are some optimized aspects on the cavity and couplers to obtain better RF performance during the high-power testing process. The traveling-wave test and full-power-reflection test were executed to check whether the coupler can afford the enough power level for the linac operation, and whether only one coupler can afford the total power for the RFQ. The construction of the testing stand, optimization of RF parameters and results of high-power RF test are presented in this paper.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL110

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THPAL123

Fabrication and Test of β=0.3 325MHz Balloon Single Spoke Resonator

cavity, niobium, linac, TRIUMF

3934

Z.Y. Yao, J.J. Keir, D. Kishi, D. Lang, R.E. Laxdal, H.L. Liu, Y. Ma, B. Matheson, B.S. Waraich, Q. Zheng, V. Zvyagintsev
TRIUMF, Vancouver, Canada

A novel balloon variant of the single spoke resonator (SSR) has been designed, fabricated and tested at TRIUMF. The cavity is the β=0.3 325 MHz SSR1 prototype for the Rare Isotope Science Project (RISP) in Korea. The balloon variant is specifically designed to reduce the likelihood of multipacting barriers near the operating point. A systematic multipacting study led to a novel geometry, a spherical cavity with re-entrant irises plus a spoke. The balloon cavity provides competitive RF parameters and a robust mechanical structure. Cold tests demonstrated the principle of the balloon concept. The fabrication experience and the preliminary test results will be reported in this paper.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL123

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THPML015

Dielectric Multipactor Discharges at 110 GHz

cavity, experiment, GUI, vacuum

4684

S. C. Schaub
MIT, Cambridge, Massachusetts, USA
M.A. Shapiro, R.J. Temkin
MIT/PSFC, Cambridge, Massachusetts, USA

A 1.5 MW, 110 GHz gyrotron has been used to experimentally measure the maximum sustainable fields on dielectric materials in vacuum. The purpose of this work is to evaluate the suitability of these materials for future applications in high frequency linear accelerators and high power terahertz components. To our knowledge, these are the first measurements of multipactor phenomena in the millimeter wave or terahertz frequency range. Materials tested include alumina, sapphire, fused quartz, crystal quartz, and high resistivity silicon. Dielectric samples were tested both as windows, with electric fields parallel to the surface, and sub-wavelength dielectric rod waveguides, with electric fields perpendicular to the surface. Surface electric fields in excess of 52 MV/m were achieved in 3 microsecond pulses. Visible light emission, absorbed/scattered microwave power, and emitted electrons were measured to characterize the discharges on the dielectric surfaces. The results of these experiments have been compared to theoretical calculations of multipactor discharges, testing these theories at significantly higher frequencies than has been done before.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML015

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