07 Accelerator Technology
T06 Room Temperature RF
Paper Title Page
TUZGBE4 Toward High-Power High-Gradient Testing of mm-Wave Standing-Wave Accelerating Structures 1224
 
  • E.A. Nanni, V.A. Dolgashev, A.A. Haase, J. Neilson, S.G. Tantawi
    SLAC, Menlo Park, California, USA
  • S. Jawla, R.J. Temkin
    MIT/PSFC, Cambridge, Massachusetts, USA
  • S. C. Schaub
    MIT, Cambridge, Massachusetts, USA
  • B. Spataro
    INFN/LNF, Frascati (Roma), Italy
 
  Funding: This work is supported in part by Department of Energy contract DE-AC02-76SF00515 (SLAC) and DE-SC0015566 (MIT).
We will preliminary testing results for single-cell accelerating structures intended for high-gradient testing at 110 GHz. The purpose of this work is to study the basic physics of ultrahigh vacuum RF breakdown in high-gradient RF accelerators. The accelerating structures consist of pi-mode standing-wave cavities fed with TM01 circular waveguide mode. We fabricated of two structures one in copper and the other in CuAg alloy. Cold RF tests confirm the design RF performance of the structures. The geometry and field shape of these accelerating structures is as close as practical to single-cell standing-wave X-band accelerating structures more than 40 of which were tested at SLAC. This wealth of X-band data will serve as a baseline for these 110 GHz tests. The structures will be powered with a MW gyrotron oscillator that produces microsecond pulses. One megawatt of RF power from the gyrotron may allow us to reach a peak accelerating gradient of 400 MeV/m.
 
slides icon Slides TUZGBE4 [4.644 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUZGBE4  
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WEPMF011 Design and Status of Sirius Light Source RF Systems 2391
 
  • R.H.A. Farias, A.P.B. Lima, L. Liu, F.S. Oliveira
    LNLS, Campinas, Brazil
 
  Sirius is the new synchrotron light source currently under construction at the site of the Brazilian Synchro-tron Light Laboratory (LNLS) in Campinas, Brazil. The facility comprises a 3 GeV electron storage ring, a full energy booster and a 150 MeV linac. This work provides a brief description of the RF system of the booster and storage ring, presenting their main characteristics and specification goals.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF011  
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WEPMF022 Coulped Multiphysics Simulation for the Water Cooling Layout of a Rhodotron Cavity 2416
 
  • L. Yang, X. He, H. Li, S.Q. Liao
    CAEP/IFP, Mainyang, Sichuan, People's Republic of China
 
  A Rhodotron-based electron accelerator served as micro-focused X-ray source is under development at IFP, CAEP. The RF-cavity, running in long pulse/ CW mode, will deliver 9 MeV energy to electron beams after multiple accelerations within the same field at a frequency of 107.5MHz. A substantial amount of average power loss with tens of kW will be dissipated on the RF surface of the cavity to maintain the operational field level. Efficient water cooling is critical to prevent large scale temperature rise for stable operation sake. Reasonable prediction of temperature rise becomes essential to assess a certain cooling layout in the design phase. The frequency drift and thermal stress on account of temperature variation and gradient on cavity wall respectively, could be computed accordingly. This paper presents a comprehensive coupled simulation involving electromagnetic, thermal and structural for the RF-cavity of Rhodotron.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF022  
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WEPMF031 Development of a High-Power High-Directivity Directional Coupler and Four Power Dividers for S-Band 2422
 
  • X. He, J. Lei, J.R. Zhang
    IHEP, Beijing, People's Republic of China
 
  A novel Bethe-hole S band directional coupler has been designed based on some structural optimizations, the prototype has been tested with a Directivity of more than 30 dB. The new directional coupler can also hold higher power compared to the old type, which is more useful for the future accelerator applications. Four power dividers using different structures are studied and the best one is chosen for fabrication. The prototype with matching rod in the middle has got qualified microwave cold test results and has been used during the whole microwave commissioning of an accelerating structure, the performance is quite stable.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF031  
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WEPMF051 Multipacting in an RF Window: Simulations and Measurements 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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WEPMF066 Fabrication of Split-Section X-band Structure Using Elastic Averaging 2521
 
  • P. Borchard, S.A. Appert, J.S. Hoh
    Dymenso LLC, San Francisco, USA
 
  Conventional accelerator structures are manufactured using axial stacks of cylindrical components which, when brazed together, form the accelerator cell structure. Splitting the accelerator structure into two sections along the beam axis allows for a significant reduction in part count and vacuum joint length. The resultant single and coplanar vacuum joint between the two split sections allows for joining techniques such as electron beam welding or brazing of the parts to form the accelerator vacuum envelope. High precision alignment of the two sections is achieved through an elastic averaging interface coupling where improved accuracy is derived from the averaging of errors over a large number of relatively compliant contacting members. The monoblock split sections allow for highly optimized cooling configurations with enhanced heat removal in high heat flux regions, reducing vacuum wall thermal stresses and enabling higher power operation. This paper describes the engineering and manufacturing of four generations of brazed and electron beam welded X-band accelerator structures at both 9.3 GHz and 11.4 GHz frequencies.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF066  
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WEPMF068 Inexpensive Brazeless Accelerator Prototype 2528
 
  • S.P. Antipov, R.A. Kostin, S.V. Kuzikov
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • A.A. Vikharev
    IAP/RAS, Nizhny Novgorod, Russia
 
  Funding: DOE SBIR
A simple, inexpensive way to manufacture a standard radio frequency (RF) driven particle accelerator is presented. The simplification comes from two innovations: utilization of LCLS gun type RF design to avoid an expensive brazing process and copper plating of stainless steel that further reduces manufacturing cost. This is realized by a special structure design where accelerating structure cells are made out of copper plated stainless steel with knife edges and structure irises - copper disks acts also as gaskets for vacuum and RF seal. Besides the reduced cost, brazeless assembly allows integration of effective cooling and magnet optics elements into accelerator cells. Here we report on manufacturing and testing of brazeless accelerator prototype.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF068  
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WEPMF069 High Shunt Impedance Accelerating Structure with Distributed Microwave Coupling 2531
 
  • S.P. Antipov, R.A. Kostin, S.V. Kuzikov
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • V.A. Dolgashev
    SLAC, Menlo Park, California, USA
 
  Funding: DOE SBIR
Conventional traveling wave or pi-phase advance standing wave structures use coupling of the microwave power through the beam pipe. This feature constrains the cavity shunt impedance (efficiency) to relatively small values. As microwave power flows through the accelerating cells in such structures, the probability of breakdown in high gradient operation is greatly increased. In this paper we present results from an accelerating structure prototype with distributed microwave coupling, an approach invented at SLAC. These structures include one or more parallel waveguides which are loaded by accelerating cavities. In this configuration accelerating cavities are fed independently and completely isolated at the beam pipe. Thus there is no microwave power flow through the accelerating cavity, making this geometry favorable for high gradient operation and maximizing the shunt impedance.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF069  
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WEPML011 Garnet Ring Measurements for the Fermilab Booster 2nd Harmonic Cavity 2700
 
  • R.L. Madrak, J.E. Dey, K.L. Duel, J. Kuharik, A.V. Makarov, W. Pellico, J. Reid, G.V. Romanov, M. Slabaugh, D. Sun, C.-Y. Tan, I. Terechkine
    Fermilab, Batavia, Illinois, USA
 
  A perpendicularly biased tuneable 2nd harmonic cavity is being constructed for use in the Fermilab Booster. The cavity's tuner uses National Magnetics AL800 garnet as the tuning media. For quality control, the magnetic properties of the material and the uniformity of the properties within the tuner must be assessed. We describe two tests which are performed on the rings and on their corresponding witness samples.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML011  
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WEPML012 Progress on the Construction of the Perpendicularly Biased 2nd Harmonic Cavity for the Fermilab Booster 2703
 
  • R.L. Madrak, J.E. Dey, K.L. Duel, M.R. Kufer, J. Kuharik, A.V. Makarov, R.D. Padilla, W. Pellico, J. Reid, G.V. Romanov, M. Slabaugh, D. Sun, C.-Y. Tan, I. Terechkine
    Fermilab, Batavia, Illinois, USA
 
  A perpendicularly biased tuneable 2nd harmonic cavity, designed for the Fermilab Booster, is being assembled for testing this summer (2018). The cavity will work at twice the frequency of the fundamental cavities, and will be on only during the injection and transition (or extraction) periods. The main purpose of adding this cavity is to improve beam capture and reduce losses as required by Fermilab's Proton Improvement Plan (PIP). After three years of testing and optimization, the cavity design has now been finalized and all constituent parts have been received. We report on the cavity final design and on the status of the construction.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML012  
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WEPML031 The New Broadband Accelerating System for the SIS18 Upgrade at GSI 2755
 
  • P. Hülsmann, R. Balß, H. Klingbeil, U. Laier, K.-P. Ningel, C. Thielmann, B. Zipfel
    GSI, Darmstadt, Germany
 
  In this contribution, a new SIS18 rf accelerating system is presented whose cavities are based on magnetic alloy materials. The rf system works at harmonic number h=2 (f=0,43- to 2,8 MHz) and provides the necessary accelerating voltage (up to 50kVp) for SIS18 injector operation for FAIR with high intensity heavy ion beams in a fast operation mode with up to three cycles per second. The paper focusses on the cavity part and its cooling issues as well as the broadband characteristics. Due the lossy magnetic alloy ring core filling, which consists of high permeability Finemet FT3M ring cores (HITACHI), the cavities show a broadband behaviour and thus no cavity tuning during the acceleration ramp is necessary. To keep the bandwidth of the cavities as broad as possible they are cooled by a special mineral oil with low permittivity. Also the beam impedance and the power consumption of the rf system are discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML031  
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WEPML032 The FAIR-SIS100 Bunch Compressor RF Station 2759
 
  • H.G. König, R. Balß, P. Hülsmann, H. Klingbeil, P.J. Spiller
    GSI, Darmstadt, Germany
  • R. Gesche, J.H. Scherer
    Aurion Anlagentechnik GmbH, Seligenstadt, Germany
  • A. Morato, C. Morri, G.T. Taddia
    OCEM, Valsamoggia, Italy
 
  In the frame of the Facility for Antiproton and Ion Research (FAIR) 9 bunch compressor RF stations were ordered for the first stage of realization of the SIS100 synchrotron. For RF gymnastics referred to as bunch rotation, one RF station has to provide a sudden rise in gap voltage of up to 40 kVp within less than 30 μs. The system is designed for a maximum RF burst of 3 ms per second. The RF frequency will be pre-selectable between 310 kHz and 560 kHz at a harmonic number of h=2 with respect to the beam. Compressed bunches with a peak current > 150 A and a width < 50 ns are the goal. For this purpose, a 1.218 m long cavity was designed using iron-based magnetic alloy cores. Variable vacuum capacitors are attached for tuning. The cavity is driven by a cross-coupled push-pull tetrode amplifier. This scheme minimizes the influence of the tetrode's DC current at the working point to the cores. The energy for the pulsed system is stored in a relatively small capacitor bank which will be charged semi-continuously and a voltage-stabilizing device is added. Cavity and power amplifier were realized by AURION Anlagentechnik GmbH ' the power supply unit is designed and built by OCEM Power Electronics.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML032  
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WEPML033 The FAIR-SIS100 Accelerating RF Station 2762
 
  • H.G. König, R. Balß, H. Klingbeil, U. Laier, D.E.M. Lens, P.J. Spiller
    GSI, Darmstadt, Germany
  • G. Blokesch, F. Wieschenberg
    Ampegon PPT GmbH, Dortmund, Germany
  • K. Dunkel, M. Eisengruber, J.H. Hottenbacher
    RI Research Instruments GmbH, Bergisch Gladbach, Germany
  • C. Hiltbrunner
    Ampegon AG, Turgi, Switzerland
 
  For the Facility for Antiproton and Ion Research (FAIR) 14 ferrite loaded accelerating RF stations are planned for the first stage of realization of the SIS100 synchrotron. Each RF station has to provide a total peak gap voltage of up to 20 kVp in CW operation - tuneable in the range of 1.1 MHz up to 3.2 MHz to allow ion beam acceleration and beam gymnastics at different harmonic numbers and energy levels in the new facility. Each RF station consists of a tuneable ferrite cavity, a single ended tetrode amplifier and a dedicated power supply and control unit (PSU) ' including two bias current supplies for cavity- and control-grid(G1)-circuit-tuning. The ferrite cavity is based on the SIS18 cavity concept but has to provide a 1.25 times higher gap voltage of 20 kVp over a total length of 3 meters. The realization is done by a consortium consisting of RI Research Instruments GmbH as consortium leader and manufacturer of the cavity, Ampegon PPT GmbH (for the tetrode amplifier) and Ampegon AG (for the power supply unit). In this contribution, the system design is discussed, and commissioning results are presented. All main parameters are achieved with the RF station described.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML033  
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WEPML034 Design and Commissioning of the RF System of the Collector Ring at FAIR 2765
 
  • U. Laier, R. Balß, A. Dolinskyy, P. Hülsmann, H. Klingbeil, T. Winnefeld
    GSI, Darmstadt, Germany
  • G. Blokesch, F. Wieschenberg
    Ampegon PPT GmbH, Dortmund, Germany
  • K. Dunkel, M. Eisengruber, J.H. Hottenbacher
    RI Research Instruments GmbH, Bergisch Gladbach, Germany
  • C. Morri, M.P. Pretelli, G.T. Taddia
    OCEM, Valsamoggia, Italy
 
  The Collector Ring (CR), a storage ring intended to perform efficient cooling of secondary beams, is under construction at GSI in the scope of the FAIR project. The RF system of the CR has to provide a frequency range from 1.1 to 1.5 MHz and pulsed gap voltages of up to 200 kVp (0.2 to 1 Hz, max. 10-3 duty cycle) and up to 10 kVp in CW operation. Five identical RF stations will be built. Each RF station consists of an inductively loaded cavity, a tetrode based power amplifier, a semiconductor driver amplifier, a switch mode power supply and two digital feedback loops. The main components of the RF station are designed, built and commissioned in close collaboration between GSI and three companies: RI Research Instruments GmbH, Ampegon PPT GmbH and OCEM Energy Technology SRL. In 2016, the first of five RF stations has been integrated at GSI. In 2017 the system was successfully commissioned to demonstrate that all envisaged parameters have been achieved. This contribution will present the requirements imposed the system, the principal design of the overall system as well as of its key components, and the results of the commissioning of the first RF station.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML034  
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WEPML043 RF Simulations of the Injector Section from CH8 to CH15 for MYRRHA 2790
 
  • P. Müller, M. Busch, H. Hähnel, K. Kümpel, D. Mäder, N.F. Petry, H. Podlech
    IAP, Frankfurt am Main, Germany
 
  Funding: Work supported by the EU Framework Programme H2020 662186 (MYRTE) and HIC for FAIR
MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is the first prototype of an accelerator driven nuclear reactor dealing with the transmutation of long-living nuclear waste. Beam quality and reliability are crucial for the reactor. The injector design is done by IAP, Goethe-University, and has been adapted to the final magnet design and voltage distributions. The energy section from 5.87 MeV up to 16.6 MeV has been changed to normal conducting CH cavities as in the lower energy part of the injector. For beam adjustment a 5-gap CH cavity rebuncher at 5.87 MeV as well as two doublet magnets forming the new MEBT-2 section between CH7 and CH8 have been added. Starting parameters for the RF simulations have been given by beam dynamics results calculated with LORASR. RF simulations of these structures consisting of flatness and tuning optimizations will be presented within this contribution.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML043  
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WEPML051 Improvement of the Chopper System for rf Deflector at the J-PARC Linac 2816
 
  • K. Futatsukawa, Z. Fang, Y. Fukui
    KEK, Ibaraki, Japan
  • Y. Sato
    Nippon Advanced Technology Co., Ltd., Tokai, Japan
  • S. Shinozaki
    JAEA/J-PARC, Tokai-mura, Japan
 
  In the J-PARC linac, the RF deflector has been operated to kick the wasted beam and to shape the intermediate-pulse like the comb structure. Then about 50% of the beam current is removed by leading the scraper and the rest beam current is injected to the downstream synchrotron ring RCS. The fast rising time and falling time, the cavity with low loading Q value in the chopper system are required to decrease the incomplete kicked beam. However, there was the ringing of the RF field on the chopper cavity, and it influenced the beam rising time. The chopper controllers, which has the fast RF -switch to make the particular RF according to the intermediate-pulses, were improved for the RF falling time by outputting short pulses with inverting phase. The beam study for the new system was successfully done. In this paper, I would like to introduce this system and to show the results of the beam study.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML051  
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WEPML055 Simulation Study of Parasitic-Mode Damping Methods for a 1.5-GHz TM020-Mode Harmonic Cavity 2822
 
  • N. Yamamoto, S. Sakanaka, T. Takahashi
    KEK, Ibaraki, Japan
 
  Design study of parasitic-mode (PM) damped structures has been conducted for the purpose to realize a normal conducting 1.5 GHz harmonic cavity which is based on the TM020 resonant mode*. We have investigated the performances of two PM-damping mechanisms, that are, rod-type antennas** and annular slots. The rod-type antennas locate at the node of electric field of the TM020 mode while the annular slots locate at the node of magnetic field. As a result of 3D electromagnetic simulations, suitable performances of PMs were confirmed by employing either of the PM-damping mechanisms. It was also shown that the slot-type structure is superior in PM-damping performance and in the unloaded Q of the TM020 mode.
* N. Yamamoto et al., IPAC'17, paper THOPIK037; N. Yamamoto Phys. Rev. Accel. Beams, 21, 1, 012001.
** T. Takahashi et al., IPAC'17, paper THPIK036.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML055  
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THPAL002 RF System Operation of High Current RFQ in ADS Project 3613
 
  • L.P. Sun, R. Huang, C.X. Li, L. Lu, A. Shi, L.B. Shi, W.B. Wang, X.B. Xu, H.W. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
  • Y. Hu
    TUB, Beijing, People's Republic of China
 
  Funding: Work supported by Natural Science Foundation of China, No.11505253
New RF system has been upgraded several times for high-current operation, especially for extra beam power and detuning angle. The current was increased gradually resulting in more and more frequency detuning, and an effective method is to tune the temperature of cavity to compromise detuning. Of course, the power dissipated in cavity and high intensity beam are approximately 120kW resulting in too many power modules operated in the high risk of failure. The specific analysis and simulation were introduced in detail.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL002  
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THPAL004 Research and Development of RF System for SC200 Cyclotron 3616
 
  • G. Chen, C. Chao, G. Liu, X.Y. Long, Z. Peng, Y. Song, Y.S. Wang, C.S. Wei, M. Xu, Q. Yang, X. Zhang, Y. Zhao
    ASIPP, Hefei, People's Republic of China
  • L. Calabretta, A.C. Caruso
    INFN/LNS, Catania, Italy
  • O. Karamyshev, G.A. Karamysheva, N.A. Morozov, E. Samsonov, G. Shirkov
    JINR, Dubna, Moscow Region, Russia
 
  A 200MeV compact isochronous superconducting cyclotron, named SC200, for proton therapy is under development by collaboration of ASIPP (Hefei, China) and JINR (Dubna, Russia). The radio frequency (RF) system as one of most significant subsystems in cyclotron consists of acceleration cavity, low level RF, RF source and transmission network. SC200 has two cavities connected in the centre, which are operated at 91.5 MHz with second harmonic. To meet the required acceleration voltage, the cavities have been carefully designed with comprised choices between several aspects, such as Q factor, mechanic stability and so on. The low-level RF (LLRF) system has been implemented by using the FPGA to achieve the significant accelerating voltage with an amplitude stability of <0.2% and a phase stability of < 0.1 degree. The cavity and LLRF system have been tested outside of cyclotron, the results will be presented. For future, the commissioning of whole RF system will be started after the assembly of SC200 at the end of 2019.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL004  
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THPAL008 A RFQ Cooler Development 3627
 
  • M. Cavenago, L. Bellan, M. Comunian, M. Maggiore, L. Pranovi
    INFN/LNL, Legnaro (PD), Italy
  • G. Maero, N. Panzeri, M. Romé
    Universita' degli Studi di Milano e INFN, Milano, Italy
 
  Funding: INFN group 5 (exp. PLASMA4BEAM)
The cooling of beams of exotic nuclei (both in energy spread and in transverse oscillations) is critical to downstream mass spectrometry devices and can be provided by collisions with light gases as in the Radio Frequency Quadrupole Cooler (RFQC). As in other traps, several electromagnetic systems can be used for beam deceleration confinement and deceleration, as a radiofrequency (rf) quadrupole, a magnetic solenoid and electrostatic acceleration. Since rf contributes both to beam cooling and heating, operational parameters should be carefully optimized. The LNL RFQC prototype is going to be placed inside the existing Eltrap solenoid, capable of providing a magnetic flux density component Bz up to 0.2 T, where z is the solenoid axis. Setup progress and related rf component development are reported; in particular simple matching boxes are discussed; the differential gas pumping system is also described.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL008  
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THPAL027 Transverse RF Deflecting Structures for the MAX IV LINAC 3684
 
  • D. Olsson, F. Curbis, E. Mansten, S. Thorin, S. Werin
    MAX IV Laboratory, Lund University, Lund, Sweden
 
  The MAX IV LINAC operates both as a full-energy injector for two electron storage rings, and as a driver for a Short Pulse Facility (SPF). A soft X-ray Laser (SXL) beamline will also be installed in the end of the existing LINAC. For SPF and SXL operation, it is important to characterize beam parameters such as bunch profile, slice energy spread and slice emittance. For these measurements, two 3 m long transverse deflecting RF structures with a matching section are being developed. The structures are operating at S-band and have variable polarizations. When fed via a SLED pulse compressor, the two structures can generate a total integrated deflecting voltage higher than 100 MV which is sufficient for measurements with temporal resolutions down to 1 fs. This paper describes the initial RF design of the deflecting structures.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL027  
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THPAL028 Commissioning of the Bunch-by-Bunch Feedback System in the MAX IV 1.5 GeV Ring 3688
 
  • D. Olsson, Å. Andersson, F.J. Cullinan, P.F. Tavares
    MAX IV Laboratory, Lund University, Lund, Sweden
 
  The MAX IV 1.5 GeV ring is an electron storage ring for production of synchrotron light in the IR to soft X-ray spectral range. The ring will deliver light to its first users during 2018. Bunch-By-Bunch (BBB) feedback has been needed to suppress coupled-bunch mode instabilities (CBMIs), and the feedback has this far been provided in all three planes by a single stripline kicker. This is done by combining the horizontal and vertical baseband feedback signals with the longitudinal feedback signal that is upconverted to the 150 MHz - 250 MHz range. The combined signal is then fed to two stripline electrodes. The layout of the BBB feedback system in the MAX IV 1.5 GeV ring is presented in this paper. Results from instability studies are also discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL028  
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THPAL033 Measurement of the Internal Dark Current in a High Gradient Accelerator Structure at 17 GHz 3705
SUSPL067   use link to see paper's listing under its alternate paper code  
 
  • 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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THPAL061 Simulation of Pulsed Temperature Rise in Cryogenic Copper RF Cavity Achieving a Very High Accelerating Field 3788
 
  • T. Tanaka, K. Hayakawa, Y. Hayakawa, K. Nogami, T. Sakai, Y. Sumitomo
    LEBRA, Funabashi, Japan
 
  A cryogenic C-band photocathode RF electron gun cavity has been studied at Nihon University LEBRA in cooperation with KEK. The RF properties of a cold model measured at 20 K have shown good agreement with those expected from computer simulations using the cavity surface resistance predicted by the theory of the anomalous skin effect. Recent studies on the vacuum RF breakdown at high electric fields suggest that the temperature in the cavity surface during the high power RF pulse has a significant effect on the behavior of the breakdown rate. In order to investigate the breakdown property of the cryogenic cavity aiming at a very high accelerating field with as low breakdown rate as possible, one-dimensional simulations of the temperature rise in the cavity surface have been done for various combinations of the RF pulse width and the peak input RF power. The evaluation will be taken into consideration in the design of a new high power cryogenic cavity that has basically the same configuration with the cold model.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL061  
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THPAL063 RF and Thermo-Mechanical Considerations in Designing the Waveguide Iris Coupler for the Drift Tube Linac in the ORNL Spallation Neutron Source 3796
 
  • S.W. Lee, Y.W. Kang
    ORNL, Oak Ridge, Tennessee, USA
 
  Funding: This work was supported by SNS through UT Battelle, LLC, under contract DE AC05 00OR22725 for the U.S.DOE
The Spallation Neutron Source (SNS) employs tapered ridge waveguide iris couplers to power six drift tube linac (DTL) cavity structures with pulsed RF systems using 2.5MW klystrons at 402.5MHz. All DTL iris couplers have been operating continuously for more than a decade without replacement. Transferring high RF energy to the cavities requires robust RF and mechanical performances with respect to power dissipation, electrical breakdown, and vacuum pressure. Considering the upcoming full 1.4MW operation and the future proton power upgrade (PPU) project, the structural design and the material selection needed to be reviewed for potential spare manufacturing. The existing design and the modified design with improvements to the coupler have been numerically studied. For the study, 3D models were used for RF and structural characterizations of the waveguide iris couplers on the DTL cavity. RF and thermo-mechanical co-simulations were performed to assess the effects of using the different materials and the structural modification.
 
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THPAL068 Status of the Polarix-TDS Project 3808
 
  • P. Craievich, M. Bopp, H.-H. Braun, R. Ganter, T. Kleeb, M. Pedrozzi, E. Prat, S. Reiche, R. Zennaro
    PSI, Villigen PSI, Switzerland
  • R.W. Aßmann, F. Christie, R.T.P. D'Arcy, U. Dorda, M. Foese, P. González Caminal, M. Hoffmann, M. Hüning, R. Jonas, O. Krebs, S. Lederer, V. Libov, B. Marchetti, D. Marx, J. Osterhoff, F. Poblotzki, M. Reukauff, H. Schlarb, S. Schreiber, G. Tews, M. Vogt, A. Wagner
    DESY, Hamburg, Germany
  • N. Catalán Lasheras, A. Grudiev, G. McMonagle, W. Wuensch
    CERN, Geneva, Switzerland
 
  A collaboration between DESY, PSI and CERN has been established to develop and build an advanced modular X-band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. This innovative CERN design requires very high manufacturing precision to guarantee highest azimuthal symmetry of the structure to avoid the deterioration of the polarization of the streaking field. Therefore, the high-precision tuning-free production process developed at PSI for the C-band and X-band accelerating structures will be used for the manufacturing. We summarize in this paper the status of the production of the prototype and the waveguide networks foreseen in the different facilities.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL068  
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THPAL070 Multi-Physics Analysis of Two Bunchers for CIFNEF 3815
 
  • Q.Y. Tan, M.J. Easton, Q. Fu, P.P. Gan, H.P. Li, Y.R. Lu, Z. Wang
    PKU, Beijing, People's Republic of China
 
  CIFNEF(Compact Intense Fast NEutron Facility) project will accelerate and deliver a 5 MeV deuteron beam to the targets to produce high-intense neutrons. A 2.5 MHz pulsed deuteron beam with bunch width within 2 ns is needed on the targets at last. To fulfill the special requirements of the beam dynamics, two types of bunchers are adopted in the CIFNEF. One is a 10.156 MHz buncher used in the low energy beam transport (LEBT) line to longitudinally focus the 50 keV deuteron beam to the RFQ longitudinal acceptance with 4 kV effective voltage. A lumped element model is adopted because of the low frequency and it consists of an inductance coil in parallel with the capacitance of drift tube. The other one is an 81.25 MHz buncher used in the high energy beam transport (HEBT) line to longitudinally focus the 5 MeV deuteron beam to 2 ns. A QWR cavity with 2-gaps is used to provide 150 kV effective voltage. Thermal and structural analyses have been carried out on these two bunchers. Details of simulations of these two bunchers are presented and discussed in this paper.  
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THPAL074 Numerical Studies of Normal Conducting Deflecting Cavity Designs for the ELBE Accelerator 3824
SUSPL066   use link to see paper's listing under its alternate paper code  
 
  • T.G. Hallilingaiah, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • A. Arnold, U. Lehnert, P. Michel
    HZDR, Dresden, Germany
 
  Currently, in the electron linac ELBE there is a single beam line. Therefore, at any given time only single user can use the beam. Moreover, as different user experiments require distinct beam intensity settings, not all the experiments fully utilize the 13 MHz CW beam capability of the facility. To utilize the full beam capacity, multiple beam lines can be established by using an array of transverse deflecting structures. For that, an RF cavity was the design choice due to its inherent advantages with respect to repeatability of the kick voltage amplitude and phase, and the possibility of CW operation in the MHz range. Potential design candidates are the CEBAF RF separator, the three proposed crab cavities for the HL-LHC upgrade project, and a novel NC deflecting cavity design. In this comparative study, the figures of merit of the cavities are computed from electromagnetic field simulations for a transverse voltage of 300 kV. This comparative study supported our selection of the deflecting cavity design for ELBE.  
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THPAL084 An X-Band Lineariser for the CLARA FEL 3848
 
  • L.S. Cowie, A.D. Brynes, J.K. Jones, A.E. Wheelhouse, P.H. Williams
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • R. Apsimon, G. Burt, W.L. Millar
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • Ö. Mete
    UMAN, Manchester, United Kingdom
  • A.J. Moss
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
 
  The CLARA FEL at Daresbury Laboratory will employ four S-band linacs to accelerate electron bunches to 250 MeV/c. In order to compress the bunch sufficiently to achieve peak currents suitable for FEL lasing, one must compensate for curvature imprinted on the longitudinal phase space of the bunch. For CLARA a harmonic RF linearization system has been designed to achieve this requirement. The linearization will be achieved by an X-band travelling wave cavity of the PSI/CERN design, which incorporates wake-field monitoring of the bunch position. A five-axis mover will align the cavity to the beam axis. Pulse compression of a 6 MW klystron pulse will provide the required power to achieve a 30 MV/m operational gradient.  
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THPAL085 High Power RF Conditioning on CLARA 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.  
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THPAL095 Metal Photocathodes Preparation for Compact Linear Accelerator at Daresbury Laboratory 3865
 
  • A.N. Hannah, J.A. Conlon, L.B. Jones, B.L. Militsyn, T.C.Q. Noakes, R. Valizadeh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • V. R. Dhanak
    The University of Liverpool, Liverpool, United Kingdom
  • L.B. Jones, B.L. Militsyn
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • S. Lederer
    DESY Zeuthen, Zeuthen, Germany
  • S. Lederer
    DESY, Hamburg, Germany
 
  The photoinjector of the CLARA FEL test facility Front End at Daresbury Laboratory is based on a S-band 10 Hz photocathode RF-gun operating with a copper photocath-ode which is driven by the third harmonic of a Ti:Sapphire laser (266 nm). The main aim of this study was to establish a procedure to prepare the Cu surface prior to installation so a Quantum Efficiency (QE) of 10-5 or higher can be achieved at laser power density below the ablation threshold of copper. The best results have been obtained by ex-situ chemical cleaning. This removed the surface oxide layer whilst at the same time producing a surface buffer layer. This inhibited the regrowth of native oxide for up to a week when exposed to normal ambient atmospheric conditions. With either chemical cleaning or Ar plasma cleaning after heating the sample in-situ to 150 °C for 90 minutes or 250 °C for 40 hours, almost all of the surface oxide was removed. For these surfaces a QE of 4.10-5 or better was measured. Oxygen plasma cleaning at 100% and 20% power produced CuO layer with surface carbon contaminant to 3 atomic %, however in-situ thermal cycling resulted in at best a QE of 3·10-6.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL095  
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THPAL108 In-Situ Characterization of Normal Conducting RF Cavities in Solaris Light Source Storage Ring 3891
 
  • P.B. Borowiec, A.I. Wawrzyniak
    Solaris National Synchrotron Radiation Centre, Jagiellonian University, Kraków, Poland
  • J. Björklund Svensson
    Lund University, Division of Atomic Physics, Lund, Sweden
 
  The SOLARIS 1.5 GeV storage ring is equipped with two 100 MHz active cavities and two 3rd harmonic passive cavities. They are in operation since 2015. For control of their respective working points, knowledge about cavity voltage and higher order mode (HOM) frequency spec-trum is mandatory. After their installation in the storage ring and connection of the RF feeder to a high power isolator and a transmitter, the influence of the external elements on the quality factor and the HOM spectrum should be verified with respect to simulations of a simpli-fied model of a stand-alone cavity. This paper will pre-sent results of in-situ cavity measurements to qualify the HOM placement and their quality factor. HOM meas-urements have been performed in the range 100 MHz to 1.3 GHz for active cavities and 300 MHz to 1.5 GHz for 3rd harmonic cavities at three different temperatures under ultra-high vacuum conditions for each cavity separately. The measurement and analysis methodology will also be presented  
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THPAL109 The New 118 MHz Cavity for RF Development Activities of the RF for Accelerator Laboratory at SLRI 3895
 
  • N. Juntong, K. Kittimanapun, P. Sunwong
    SLRI, Nakhon Ratchasima, Thailand
  • A. Sutchada
    Walailak University, Nakhon Si Thammarat, Thailand
 
  The RF for accelerator laboratory is established at SLRI to perform RF related development activities of the current light source and the future synchrotron light facility in Thailand. One of activities is to build an in-house RF cavity. It will be used for testing of RF amplifier unit and the developed LLRF system. The cavity is a nose-cone pill-box cavity operating at 118 MHz and aiming at 100 kV gap voltage. Details of designing in particular the inner surface profile, the RF properties, the higher order modes properties, the RF power coupler, and the tuning mechanism will be presented with the manufacturing timeline.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL109  
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THPAL110 High-Power RF Test of Coaxial Couplers for the Injection Linac of XiPAF 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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THPAL112 RF Matching Circuit for CANREB RFQ 3902
 
  • T. Au, B. Barquest, J.J. Keir, V. Zvyagintsev
    TRIUMF, Vancouver, Canada
 
  A RF matching circuit has been developed to provide two phase RF voltage of 1.2 kVpp at 3 MHz and 6 MHz for the CANREB RFQ structure with an equivalent capacitive load of 300 pF. The RF matching circuit utilizes pi-network with two phase transformer. Beyond RF drive the CANREB structure requires pulse DC bias with amplitude up to 500 V. Results of development and testing of RF matching circuit and filters are presented in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL112  
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THPAL113 The Design of 1 MeV Proton LINAC Operating in CW 3905
 
  • N.V. Avreline
    TRIUMF, Vancouver, Canada
 
  Experimental results and computer simulations of electrodynamic and thermodynamic characteristics are presented for an accelerating structure that is excited in the TM010 mode and that has the accelerating channel of URAN-1M located in the diametric plane. The idea of using this structure in the particle accelerator URAN-1M, located at the Baikov Institute of Metallurgy and Materials Science, with the goal of increasing the average beam current is explored.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL113  
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THPAL114 The Analytical Model of the Helical Accelerating Structure of Linac with Helix Outside of the Vacuum Chamber 3908
 
  • N.V. Avreline
    TRIUMF, Vancouver, Canada
 
  An analytical model of the helical RF resonator for the single charged 250 keV nitrogen ion implanter operating in CW was developed. The analytical model allowed to determine the geometry of the accelerating structure and to construct CST Microwave Studio and ANSYS HFSS models based on this analytical model. Results obtained from the analytical model and simulations were within 5% of each other. The experimental investigation of the accelerating section confirmed that the models are correct. The accelerating section was tuned and verified for the right accelerating field distribution and operating frequency. Finally, the section was successfully tested in 2 kW CW RF power.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL114  
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THPAL115 The Design of 1.1 MW RF Dummy Load for the RF System of 520 MeV Cyclotron 3911
 
  • N.V. Avreline, Y. Bylinskii, B. Jakovljevic, Y. Ma, V. Zvyagintsev
    TRIUMF, Vancouver, Canada
 
  The RF System of 520-MeV Cyclotron is operating at 23 MHz with 1 MW CW RF power. The RF dummy load is required to troubleshoot and tune the RF amplifier. The RF system is being constantly improved and the future goal is to increase cyclotron's beam current up to 400 μA, which requires increasing the RF amplifier's power. As a part of this goal, a new RF dummy load was designed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL115  
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THPAL122 Beam Performance Study of an RF Structure to Accelerate or Bunch Low Energy Ion Beams 3931
 
  • S.D. Rädel, S. Kiy, R.E. Laxdal, O. Shelbaya
    TRIUMF, Vancouver, Canada
 
  The 35.4MHz Radio Frequency Quadrupole (RFQ) at the ISAC-I facility at TRIUMF is designed to accelerate ions from an energy of 2.04 keV/u to 150 keV/u for a large range of mass-to-charge ratios (A/Q). A multi-harmonic, 11.8MHz, buncher is used to provide a time focus at the RFQ entrance. Due to limits in the ion source HV platform a boost in the energy is required for higher mass beams (20 ≤ A/Q ≤ 30) to provide energy matching into the RFQ. To achieve this, a 3-gap, 11.8 MHz RF booster has been installed into the ISAC-I facility downstream of the buncher and upstream of the RFQ. The device can operate as an accelerator to match into the RFQ or as a second pre-buncher to improve capture in the RFQ and reduce sensitivity to space charge. Proof-of-principle measurements demonstrating various aspects of the performance will be reported and compared against expectations.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL122  
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THPAL149 RF System Based on Two Klystrons and Phase Modulation for Photo-Cathode Injector 3996
 
  • P. Wang, D.Z. Cao, H.B. Chen, J. Shi, Z.H. Wang, H. Zha
    TUB, Beijing, People's Republic of China
 
  We proposed an RF system with two klystrons, of which the powers are combined by a 3dB-hybrid. By managing the phases of the two klystrons respectively, the two pulses from the two output ports of the 3dB-hybrid can be of different powers, phases, and shapes. One of the two pulses can be set to an RF gun, while the other one can feed traveling accelerating structures. Two methods of phase modulation were proposed based on this scheme. Comparing with the state-of-art RF system, the new one can be of high efficiency or can generate electron beams with higher energy. The detailed analysis of the two methods and some experiments are described in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL149  
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THPAL150 Development of Tsinghua X-Band High Power Test Facility 3999
 
  • M.M. Peng, D.Z. Cao, W. Gai, Y.L. Jiang, J. Liu, J. Shi, P. Wang
    TUB, Beijing, People's Republic of China
 
  The X band high power test facility consists of a 11.424 GHz, 50 MW CPI klystron and a ScandiNova pulse modulator at Tsinghua University has been built since Sept 2017 and the output RF power has reached 60 MW with 200 ns pulse width at a repetition frequency of 10. The klystron output RF pulse will eventually be 50 MW at a 1.5 μs. A group of cylinder pulse compressor will be installed. High gradient accelerating structures for research and TTX will be tested on this facility.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL150  
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THPAL151 Progress in Understanding Breakdown Characteristics of X-Band Choke-Mode Structures 4002
 
  • X.W. Wu, D.Z. Cao, H.B. Chen, J. Shi, H. Zha
    TUB, Beijing, People's Republic of China
  • T. Abe, T. Higo, S. Matsumoto
    KEK, Ibaraki, Japan
 
  Funding: National Natural Science Foundation of China (Grant No. 11135004).
As one of the higher-order-mode (HOM) damping structures, X-band choke-mode accelerating structures had been studied for several years. However, the breakdown characteristics of the X-band choke are still unknown. Five different single-cell choke-mode accelerating structures and one reference structure were designed, fabricated and high-gradient tested to study the related RF breakdown characteristics. The absence of field emission current flash was proposed to be the sign of breakdowns occurring inside the choke, this was verified by the post-mortem observation. Evaluation of the breakdown rate revealed that there is memory effect with pulse width and electric field. The breakdown rate in a single RF pulse did not have the 5th order pulse width and 30th order electric field dependency predicted by the empirical formula.
 
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THPAL152 Study of X-Band Phase Shifter Using Ferrite Material 4005
 
  • Y.L. Jiang, D.Z. Cao, H.B. Chen, J. Shi, P. Wang, H. Zha
    TUB, Beijing, People's Republic of China
 
  Ferrite has the feature of the permeability depended on the external static magnetic field, thus could be used to shift the phase of the propagating radio frequency (RF) signal. In this paper, we introduce a novel design of ferrite-based RF phase shifter. The design changes the resonant frequency of a ferrite-filled pill-box cavity to implement the phase changing. This design has a lower local RF field and a higher sensitivity on the phase changing than those of waveguide phase shifter, which may bring advantages such as higher power capacity, fast changing speed and lower insertion loss. Theory and simulation results are also presented in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL152  
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THPAL153 High Power Test of the S-Band Spherical Pulse Compressor at Tsinghua University 4008
 
  • P. Wang, D.Z. Cao, H.B. Chen, C. Cheng, J. Shi, Z.H. Wang, H. Zha
    TUB, Beijing, People's Republic of China
 
  We designed, fabricated and high power tested an S-band spherical pulse compressor for the high-power test facility at Tsinghua University. The pulse compressor comprises a spherical resonant cavity with an unloaded quality factor of 100, 000 and an RF polarizer with two rectangular ports and a circular port. To achieve high efficiency and large power gain, the coupling coefficient was optimized to 8 with input pulse length of 3.6 us and compression ratio of 12. After conditioning the RF system, the pulse compressor generated RF pulses with peak power of more than 400MW. And during the operation, the pulse compressor has very low breakdown rate and was extremely stable.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL153  
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THPAL154 High-Gradient Performance of X-Band Choke-Mode Structures 4011
 
  • X.W. Wu, D.Z. Cao, H.B. Chen, J. Shi, H. Zha
    TUB, Beijing, People's Republic of China
  • T. Abe, T. Higo, S. Matsumoto
    KEK, Ibaraki, Japan
 
  Funding: National Natural Science Foundation of China (Grant No. 11135004)
The choke-mode accelerating structure is one of the higher-order-mode (HOM) damping structures. It has the advantage of relatively simple fabrication and low surface magnetic field. C-band choke-mode accelerating structures have been successfully applied in multibunch XFEL. However, the X-band choke-mode study remains in the theoretical design stage. The high-gradient performance of the choke is still unknown. Five different single-cell choke-mode accelerating structures were designed, fabricated and high-gradient tested to study the related RF breakdown characteristics. It was observed that high electric field and small choke dimension caused serious breakdowns in the choke which was the main limitation of the high-gradient performance. The Choke-mode accelerating structures reached 130 MV/m by decreasing the electric field and increasing the choke gap. A new quantity was proposed to give the high-gradient performance limit of choke-mode accelerating structures due to RF breakdown. The new quantity was obtained from the summary of the high-gradient experiments and could be used to guide high-gradient choke-mode accelerating structure design.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL154  
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THPAL155 Fabrication and Cold Test of the Correction Cavity Chain for Klystron-Based CLIC 4014
 
  • P. Wang, D.Z. Cao, H.B. Chen, J. Shi, Z.H. Wang, H. Zha
    TUB, Beijing, People's Republic of China
 
  A proposed RF scheme based on correction cavity chain and storage cavity (CC-SC scheme) for klystron-based CLIC has the ability to generate flat output pulses. In the scheme, the correction cavity chain modulates the amplitude of the input pulse, while the storage cavity compresses the amplitude-modulated pulse. Resonant cavities of the correction cavity chain are of a relatively low unloaded quality factor and of small size, which results in the compactness of the RF scheme. The first prototype of a correction cavity chain was fabricated and cold tested at Tsinghua University and then delivered to CERN for high power test. Both the results of the cold and high power tests show that the correction cavity chain is of good performance. Feasibility and stability of the pulse compression system based on CC-SC scheme were demonstrated.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL155  
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THPAL156 High-Power Test of a Compact X-Band RF Rotary Joint 4017
 
  • J. Liu, H.B. Chen, J.Q. Qiu, J. Shi, Z.H. Wang, X.W. Wu, H. Zha
    TUB, Beijing, People's Republic of China
 
  A compact X-band (9.3 GHz) RF rotary joint has been developed in the accelerator laboratory of Tsinghua University. Cold measurements on the rotary joint using Vector-Network showed good results. In recent high-power tests, the RF rotary joint was operated under a 1.6 MW X-band magnetron. The incident power, the transmitted power and the pulse width of this rotary joint have been measured. The transmitted power kept stable in different rotation angle. In this paper, the setup and results of the high-power tests of this RF rotary joint are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL156  
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THPAL158 Development of an Half-Cell Accelerating Structure in Tsinghua 4023
 
  • M.M. Peng, W. Gai, J. Shi, Z.H. Wang, H. Zha
    TUB, Beijing, People's Republic of China
 
  The half-cell high gradient accelerating structure is attractive for its easy manufacturing and good alignment. A structure with 12 cells has been designed for the frequency of 11.424 GHz and a cold test will be conducted. Two different mechanical factory manufacture with same machining drawing and the results will be compared.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL158  
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THPML047 Design and Measurement of the X-Band Pulse Compressor for TTX 4745
 
  • Y.L. Jiang, H.B. Chen, C. Cheng, W. Gai, J. Shi, P. Wang, Z.H. Wang, X.W. Wu, H. Zha
    TUB, Beijing, People's Republic of China
 
  A radio frequency (RF) pulse compressor had been designed for the X-band (11.424 GHz) high power test stands at the Accelerator Laboratory of Tsinghua University. It is the SLED-I type pulse compressor, which uses a high quality factor corrugated circular cavity to store the RF power. An RF polarizer couples two quadrature modes into the cavity so that the pulse compressor needs only one cavity. The cavity implements HE1-1-14 mode, with the Q0 of 115, 000 and the coupling factor (β) of 3.23. The design and the microwave measurement before brazing of this pulse compressor are presented in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML047  
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