WG4: Superconducting RF
Paper Title Page
TUCOYBS01
KEK ERL SRF Operation Experience  
 
  • H. Sakai, T. Furuya, E. Kako, T. Konomi, T. Miura, F. Qiu, K. Umemori
    KEK, Ibaraki, Japan
 
  We will present the SRF operation experience during long-term cERL operation in KEK.  
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TUCOYBS03
Superconducting Twin-Axis Cavity for ERL Applications  
 
  • H. Park, J.R. Delayen
    ODU, Norfolk, Virginia, USA
  • H. Park
    JLab, Newport News, Virginia, USA
 
  Superconducting cavities with two beam pipes have been proposed in the past for energy recovery linac applications. The relatively complex geometry of those cavities presented a serious challenge for fabrication and surface processing. Main concerns have now been overcome with the production and successful RF testing of a new elliptical twin-axis cavity proposed by Jefferson Lab and optimized by the Center for Accelerator Science at Old Dominion University in the frame of a DoE accelerator stewardship program. The cavity design provides uniform accelerating or decelerating fields for both beams. This paper describes the cavity design, fabrication experience, and the first cold RF test results and explores potential applications especially for the proposed Jefferson Lab electron-ion Collider (JLEIC).  
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TUCOYBS04
Integration of the MESA Modules to BERLinPro for High Power Beam Tests  
 
  • F. Hug, S.D.W. Thomas
    KPH, Mainz, Germany
 
  Funding: This work has been supported by DFG through the PRISMA+ cluster of excellence EXC 2118/2019 and by the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 730871.
MESA and BERLinPro are two Energy Recovery Linac (ERL) projects, both currently under construction at Germany. Both projects are running on the TESLA operation frequency of 1.3 GHz. Despite the different goals for future operation and achievable beam current the main linac cryomodule of MESA is planned to be integrated into the BERLinPro ring in order to perform high current beam tests. This unique opportunity is beneficial for both projects. Nevertheless, there are some challenges coming with the integration of the modules at Berlin. We will give an overview of the planned experiments and will report in particular on the adaption of SRF and cryosystems. Despite the diverse goals, the main linac, providing the larger part of the particles energy, is fairly compatible. It is planned to test and run the MESA linac module in BERLinPro, prior to its usage in MESA. The goals and benefits of this unique cooperation for both projects are outlined in this paper. The necessary adaptions in BERLinPro, including hardware aspects, the new optics, and the scope of performance are outlined in the paper.
 
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TUCOZBS02 A Ferroelectric Fast Reactive Tuner (FE-FRT) to Combat Microphonics 42
 
  • N.C. Shipman, J. Bastard, M.R. Coly, F. Gerigk, A. Macpherson, N. Stapley
    CERN, Geneva, Switzerland
  • I. Ben-Zvi
    BNL, Upton, New York, USA
  • G. Burt, A. Castilla
    Lancaster University, Lancaster, United Kingdom
  • C.-J. Jing, A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • E. Nenasheva
    Ceramics Ltd., St. Petersburg, Russia
 
  A prototype Fast Reactive Tuner (FRT) for superconducting cavities has been developed, which allows the frequency to be controlled by application of a potential difference across a newly developed ultra-low loss ferro-electric material residing within the tuner. The tuner operates at room temperature, outside of the cryostat and coupled to the cavity via an antenna and co-axial cable. This technique allows for active compensation of microphonics, eliminating the need to design over-coupled fundamental power couplers and thus significantly reducing RF power particularly for low beam current applications. Modelling; simulation; and stability analysis, of the tuner; cavity; measurement system; and feedback loop, have been performed in the frequency and time domain, and are compared to the latest experimental results. The potential benefits of applying this techniques to ERLs, which are seen as one of the major use cases, are detailed both in general and with regards to specific projects. Ideas and designs for an improved next generation FRT are also discussed.  
slides icon Slides TUCOZBS02 [5.607 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-TUCOZBS02  
About • paper received ※ 17 September 2019       paper accepted ※ 06 November 2019       issue date ※ 24 June 2020  
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TUCOZBS04 Characterization of Microphonics in the cERL Main Linac Superconducting Cavities 48
 
  • F. Qiu, D.A. Arakawa, M. Egi, E. Kako, H. Katagiri, T. Konomi, T. Matsumoto, S. Michizono, T. Miura, H. Sakai, K. Umemori
    KEK, Ibaraki, Japan
  • M. Egi, S. Michizono
    Sokendai - Hayama, Hayama, Japan
  • E. Kako, T. Konomi, T. Matsumoto, T. Miura, F. Qiu, H. Sakai, K. Umemori
    Sokendai, Ibaraki, Japan
 
  In the main linac (ML) of the KEK-cERL, two superconducting cavities with high loaded Q (QL ¿ 1×107) are operated in continuous wave (CW) mode. It is important to control and suppress the microphonics detuning owing to the low bandwidth of the cavities. We evaluated the background microphonics detuning by the low level radio frequency system during the beam operation. Interestingly, a ¿field level dependence microphonics¿ phenomenon was observed on one of the cavities in the ML. Several frequency components were suddenly excited if the cavity field is above a threshold field (~3 MV/m). We found that this threshold field is probably related with the cavity quench limits despite the unclear inherent physical mechanism. Furthermore, in order to optimize the cavity resonance control system for better microphonics rejection, we have measured the mechanical transfer function between the fast piezo tuner and cavity detuning. Finally, we validated this model by comparing the model response with actual system response.  
slides icon Slides TUCOZBS04 [7.564 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-TUCOZBS04  
About • paper received ※ 13 September 2019       paper accepted ※ 01 November 2019       issue date ※ 24 June 2020  
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TUCOZBS05 Low Level RF ERL Experience at the S-DALINAC* 52
 
  • M. Steinhorst, M. Arnold, T. Bahlo, R. Grewe, L.E. Jürgensen, J. Pforr, N. Pietralla, F. Schließmann, S. Weih
    TU Darmstadt, Darmstadt, Germany
 
  Funding: *Supported by the DFG through GRK 2128.
The recirculating superconducting Darmstadt linear accelerator S-DALINAC [1] is one of the main research instruments at the institute for nuclear physics at the TU Darmstadt. It is operating in cw mode at beam currents of up to 20 uA with energies of up to 130 MeV using a thrice recirculating scheme. In 2010 the present digital low-level rf (LLRF) control system was set into operation. Since 2017 the S-DALINAC can be used as an energy recovery linac (ERL). The ERL mode is adjusted by shifting the phase of the beam by 180° in the second recirculation. The current setup of the LLRF control system is not optimized for the usage in an ERL operation. Therefore investigations in regard of the rf control performance have to be done. The first successful one turn ERL operation was set up in August 2017 where the rf control performance was investigated the first time in this new mode. In this talk the LLRF control system of the S-DALINAC is presented and its perfomance during an ERL operation is discussed.
*[1] N. Pietralla, Nucl. Phys. News 28 No. 2, 4 (2018).
 
slides icon Slides TUCOZBS05 [26.760 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-TUCOZBS05  
About • paper received ※ 13 September 2019       paper accepted ※ 01 November 2019       issue date ※ 24 June 2020  
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TUCOZBS06 Cryomodules for the Mainz Energy-Recovering Superconducting Accelerator (MESA) 56
 
  • T. Stengler, K. Aulenbacher, F. Hug, D. Simon, C.P. Stoll, S.D.W. Thomas
    KPH, Mainz, Germany
  • K. Aulenbacher
    HIM, Mainz, Germany
  • K. Aulenbacher
    GSI, Darmstadt, Germany
 
  Funding: This work is supported by the German Research Foundation (DFG) under the Cluster of Excellence "PRISMA+" EXC 2118/2019}
The Mainz Energy-recovering Superconducting Accelerator (MESA) will be an electron accelerator allowing c.w. operation in energy-recovery (ER) mode. The energy gain of 50 MeV will be provided by two modified ELBE/Rossendorf-type cryomodules. The MESA-cryomodules are delivered and tested. The test results will be discussed.
 
slides icon Slides TUCOZBS06 [10.644 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-TUCOZBS06  
About • paper received ※ 16 September 2019       paper accepted ※ 11 November 2019       issue date ※ 24 June 2020  
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WEPNEC04
HOM Damping for High Current SRF Cavity  
 
  • W. Xu
    BNL, Upton, New York, USA
 
  Funding: * Work supported by LDRD program of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
High power HOM damper is a challenge for high current SRF accelerator. In the past few years, we developed two types of high power HOM damper: a novel rigid waveguide high power HOM damping scheme and a room temperature SiC beampipe absorbing scheme. This presentation will present the design and test results of these two HOM damping schemes.
 
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WEPNEC14 Electromagnetic Design of a Superconducting dual axis Spoke Cavity* 94
 
  • Ya.V. Shashkov, N.Yu. Samarokov
    MEPhI, Moscow, Russia
  • I.V. Konoplev
    JAI, Oxford, United Kingdom
 
  Funding: The reported study was funded by RFBR according to the research project 18-302-00990
Dual axis superconducting spoke cavity for Energy Recovery Linac application is proposed. Conceptual design of the cavity is shown and preliminary optimiza-tions of the proposed structure have been carried out to minimize the ratio of the peak magnetic and electric fields to the accelerating voltage. The new design and future work are discussed
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-WEPNEC14  
About • paper received ※ 01 October 2019       paper accepted ※ 06 November 2019       issue date ※ 24 June 2020  
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THCOWBS03 System Identification Procedures for Resonance Frequency Control of SC Cavities 129
 
  • S. Orth, H. Klingbeil
    TEMF, TU Darmstadt, Darmstadt, Germany
 
  Funding: Work supported by Deutsche Forschungsgemeinschaft (DFG): GRK 2128 ’AccelencE’
Energy Recovery Linacs promise superior beam quality: sharper and more intense. To reach these goals, resonance frequency control of the superconducting RF cavities is an important part. In this work, system identification procedures conducted at components of the S-DALINAC (Institute for Nuclear Physics, TU Darmstadt, Germany) are shown. This includes investigations of the piezo tuner’s effect on, e.g., the phase of the accelerating field when a periodic disturbance is applied. The results are compared to simulations of the modelled system and the impact of the applied controller is discussed.
 
slides icon Slides THCOWBS03 [0.593 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-THCOWBS03  
About • paper received ※ 17 September 2019       paper accepted ※ 01 November 2019       issue date ※ 24 June 2020  
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THCOWBS05
The Development of HOM-damped 166.6MHz SRF Cavities for High Energy Photon Source in Beijing  
 
  • P. Zhang, J. Dai, R. Ge, R. Han, T.M. Huang, S.P. Li, Z.Q. Li, H.Y. Lin, Q. Ma, Z.H. Mi, Q.Y. Wang, X.Y. Zhang
    IHEP, Beijing, People’s Republic of China
 
  Funding: This work has been supported by HEPS-TF project and partly by Pioneer "Hundred Talents Program" of Chinese Academy of Sciences.
High Energy Photon Source is a 6GeV kilometer-scale synchrotron light source to be built in Beijing. The designed beam emittance is lower than 100pm.rad approaching diffraction limitation with 200mA beam current stored. In order to realize a novel injection scheme and prolong the beam lifetime, a double-frequency RF system has been proposed with 166.6MHz as the fundamental and 499.8MHz as the third harmonic. Both RF system will adopt superconducting cavities. Over the last three years, a 166.6MHz quarter-wave β=1 proof-of-principle SRF cavity has been in-house developed, vertical tested, dressed with helium jacket and ancillaries, and eventually horizontal tested with a success in early 2019. In parallel, the HOM-damped prototype cavity has been designed adopting a hybrid damping scheme. Due to a rather low-frequency HOMs, both HOM couplers and beam-pipe HOM absorbers are to be used to ensure a tight impedance budget.
 
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THCOWBS06 Beam Breakup Limit Estimations and Higher Order Mode Characterisation for MESA 134
 
  • C.P. Stoll, F. Hug
    KPH, Mainz, Germany
 
  Funding: Work supported by the German Research Foundation (DFG) under the Cluster of Excellence "PRISMA+" EXC 2118/2019, through RTG2128 Accelence and by ARIES.
MESA is a two pass energy recovery linac (ERL) currently under construction at the Johannes Gutenberg-University in Mainz. MESA uses two 1.3 GHz TESLA type cavities with 12.5 MV/m of accelerating gradient in a modified ELBE type cryomodule in c.w. operation. One potential limit to maximum beam current in ERLs is the transverse beam breakup (BBU) instability induced by dipole HOMs. These modes can be excited by bunches passing through the cavities off axis. Following bunches are then deflected by the HOMs, which results in even larger offsets for recirculated bunches. This feedback can even lead to beam loss. To measure the quality factors and frequencies for the dressed as well as undressed cavities improves the validity of any current limit estimation done.
 
slides icon Slides THCOWBS06 [3.256 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-THCOWBS06  
About • paper received ※ 18 September 2019       paper accepted ※ 04 November 2019       issue date ※ 24 June 2020  
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THCOWBS07
Passive and Active Control of Microphonics at CBETA and Elsewhere  
 
  • N. Banerjee, G.H. Hoffstaetter, M. Liepe, P. Quigley
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: This work was performed through the support of New York State Energy Research and Development Agency (NYSERDA).
Superconducting Radio Frequency (SRF) cavities operating with large loaded quality factors is the natural choice for Energy Recovery Linacs which operate at negligible beam loading. While this leads to lower RF power requirements, the stability of the accelerating field is strongly influenced by peak microphonics detuning. In this talk, I will discuss various methods of passively suppressing vibrations used in various facilities using low bandwidth SRF systems, with special reference to CBETA, a multi-turn SRF ERL being commissioned at Cornell University. I will also describe our active microphonics control system based on a modified narrow band Active Noise Control (ANC) algorithm and compare it with schemes being explored in other machines.
 
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THCOXBS01
Waveguide HOM Loads for High Current Elliptical Cavities  
 
  • J. Guo, R.A. Rimmer
    JLab, Newport News, Virginia, USA
  • H.-W. Glock, A.V. Vélez
    HZB, Berlin, Germany
 
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from Helmholtz Zentrum Berlin
Waveguide HOM dampers are widely used in high current RF cavities, as waveguides are natural high pass RF filters and can easily handle high RF power. In this presentation, the author will review a few typical waveguide HOM load designs, especially the recently developed high power HOM loads for BERLinPro and BESSY-VSR. We will report the RF-thermal-mechanical design, fabrication technology, absorber material choice, as well as the testing results of these HOM loads.
 
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THCOXBS02 Development of HOM Coupler with C-Shaped Waveguide for ERL Operation 138
 
  • M. Sawamura, R. Hajima
    QST, Tokai, Japan
  • M. Egi, K. Enami, T. Furuya, H. Sakai, K. Umemori
    KEK, Ibaraki, Japan
 
  HOM damping in the superconducting cavities has been becoming increasingly important for high current beam acceleration. Though some HOM damping devices have already been used with success at moderate currents, they have some inherent disadvantages for high current in principle. We have proposed the new type of the HOM coupler using the C-shaped wave guide (CSWG). The CSWG is structured by topologically transforming a rectangular waveguide into coaxial-like structure whose inner and outer conductors are connected with a plate. Similar to the rectangular waveguide, the CSWG has cutoff frequency whose half wave length is approximately equal to the mean circumference. This enables a smaller low-pass filter than the rectangular waveguide. Since the inner conductor can be easily cooled through the plate and the outer conductor, this prevents the connector for HOM power extraction from temperature rising. These characteristics of the CSWG-type HOM coupler can solve the disadvantages of the conventional damping devices. The properties of sufficient HOM damping were confirmed by the measurements with the CSWG-type HOM couplers equipped to the cavity models.  
slides icon Slides THCOXBS02 [7.418 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-THCOXBS02  
About • paper received ※ 13 September 2019       paper accepted ※ 01 November 2019       issue date ※ 24 June 2020  
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THCOXBS05
High Q 704 MHz Cavity Tests at CERN  
 
  • A. Macpherson
    CERN, Geneva, Switzerland
 
  Results from CERN’s bulk niobium high-gradient cavity development program at CERN are presented, with particular focus on evolution of RF performance 704 MHz bulk niobium 5-cell elliptical cavity prototypes originally produced for the Superconducting Proton Linac (SPL) project. Successive cold tests of bare cavities have been used to refine the cavity preparation and testing process, with all steps done in-house at CERN, and reproducible RF performance well above SPL specifications has been achieved. Current performance results are discussed in relation to cavity preparation and cold tests procedures, with reference to direct observables such as expelled flux and thermal gradients during cool down, field emission characteristics, and quench diagnostics. In addition, the processing of raw RF data from single pulse measurements to extract RF performance figures of merit will be presented, offering an alternative approach to assessing RF performance.  
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THCOXBS06
Degradation and Recovery of Cavity Performance in Compact-ERL Injector Cryomodule at KEK  
 
  • E. Kako
    KEK, Ibaraki, Japan
 
  After cryomodule assembly and first cool-down tests in 2012, the cERL injector cryomodule has been stably operated with beam for eight years. However, gradual increases of x-ray radiation levels due to field emission were observed during the long term beam operation. High power pulsed RF conditioning as a cure method was firstly applied in the cool-down period in 2016, so that degraded cavity performances have almost recovered up to the previous levels. After that, high power pulsed RF conditioning has been repeatedly carried out as a standard procedure in the beginning of the cool-down periods in 2017-2019. Performance degradation and recovery status during the long term beam operation will be presented in this talk.  
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FRCOYBS04 Working Group Summary: Superconducting RF 177
 
  • F. Gerigk
    CERN, Meyrin, Switzerland
  • P.A. McIntosh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
 
  To be added  
slides icon Slides FRCOYBS04 [17.955 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-FRCOYBS04  
About • paper received ※ 20 September 2019       paper accepted ※ 01 November 2019       issue date ※ 24 June 2020  
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