Keyword: multipactoring
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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 icon Slides TUZGBE3 [1.830 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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