MC7: Accelerator Technology
T06 Room Temperature RF
Paper Title Page
MOXB03
 Copper Based Radio Frequency Structures: Are We at the End of Road for This Technology?  
 
  • S.G. Tantawi
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by Department of Energy contract DE-AC03-76SF00515.
We will present an overview of recent advances in high gradient copper structures operating at room temperature and at cryogenic temperature. We will include the advances that enabled us to understand better the underlying fundamental physics that govern the breakdown phenomena in high field vacuum structures. We will then present the recent advances in linac topologies that take advantage of this basic understanding of the breakdown phenomena. We will also showcase how these advances are being utilized for many different medical, industrial, and discovery machines. Our presentation will not be limited to electron accelerators but will also include advances for high gradient hadron linacs. 		 
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MOPAB155 Magnetic Breakdowns in Side-Coupled X-Band Accelerating Structures 540
 
  • S.P. Antipov, P.V. Avrakhov, S.V. Kuzikov
    Euclid TechLabs, Solon, Ohio, USA
  • V.A. Dolgashev
    SLAC, Menlo Park, California, USA
  • C. Jing
    Euclid Beamlabs, Bolingbrook, USA
  
  Funding: DOE SBIR
Side coupled accelerating structures are popular in the industrial realizations of linacs due to their high shunt impedance and ease of tuning. We designed and fabricated a side-coupled X-band accelerating structure that achieved 133 MOhm/m shut impedance. This structure was fabricated out of two halves using a novel brazeless approach. The two copper halves are joined together using a stainless steel joining piece with knife edges that bite into copper. This structure had been tested at high power at SLAC National Accelerator Laboratory. The performance of the structure had been limited by magnetic breakdowns on the side-coupling cells. In this paper we will present results of the high gradient tests and after-test analysis. Scanning electron microscopy images show a typical magnetic-field induced breakdown. 		 
poster icon Poster MOPAB155 [1.069 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB155  
About • paper received ※ 20 May 2021       paper accepted ※ 23 June 2021       issue date ※ 01 September 2021  
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MOPAB322 Electronics for Bead-pull Measurement of Radio Frequency Accelerating Structures in LEHIPA 993
 
  • S. Rosily, S. Krishnagopal
    Homi Bhbha National Institute (HBNI), DAE, Mumbai, India
  • S. Krishnagopal, S. Singh
    BARC, Mumbai, India
  
  For carrying out bead-pull characterisation of RFQ and DTL at the Low Energy High Intensity Proton Accelerator of BARC, a controller for simultaneous motion of 64 axis, tuners or post couplers, was developed. Also, a bead motion controller with integrated phase measurement sensor was developed. The paper discusses the requirements of the system, the architecture of the control systems, operation and results. The results obtained from the sensor was compared to that obtained using an independent USB VNA. The advantages of the system especially with addition of internal phase measurement sensor including minimising position error, flexibility in beadpull to selectively increase resolution at specified locations and ease of implementing auto-tuning algorithms are discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB322  
About • paper received ※ 20 May 2021       paper accepted ※ 24 May 2021       issue date ※ 14 August 2021  
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MOPAB329 Operations of Copper Cavities at Cryogenic Temperatures 1020
 
  • H. Wang, U. Ratzinger, M. Schuett
    IAP, Frankfurt am Main, Germany
  
  How the anomalous skin effect by copper affects the efficiency of copper- cavities will be studied in the experiment, especially at lower temperatures. The accurate quality factor Q and resonant frequency of three coaxial cavities will be measured over the temperature range from 300 to 22 K. The three coaxial cavities have the same structure, but different lengths, which correspond to resonant frequencies: around 100 MHz, 220 MHz and 340 MHz. The motivation is to check the feasibility of an efficient pulsed, liquid nitrogen cooled ion linac.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB329  
About • paper received ※ 19 May 2021       paper accepted ※ 07 June 2021       issue date ※ 02 September 2021  
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MOPAB330 Production and Performance Evaluation of a Compact Deflecting Cavity to Measure the Bunch Length in the cERL 1023
 
  • D. Naito, Y. Honda, T. Miyajima, N. Yamamoto
    KEK, Ibaraki, Japan
  
  At the KEK compact energy recovery linac, we try to generate an infrared free-electron laser (FEL). To generate the FEL, an electron bunch should be compressed along the longitudinal direction. The measurement of the bunch length is key to optimize the bunch compression. We plan to measure the bunch length by deflecting cavities in the burst mode. The deflecting cavities are required to be a time resolution of 33 fs in order to not only measure the bunch length but also resolve the structure inside the electron bunch. To achieve the requirement, we developed a c-band cavity whose RF input port is compact. The deflecting cavity is a single cell and normal conducting cavity. The deflection mode of the cavity is TM110. The 12 cavities will be located at the exit of undulators. In this presentation, we explain the design of our cavity and report the production of the first cavity. We also report the evaluation of the resonance frequency, the unloaded Q and the external Q of the cavity. From the measurements and simulations, the R/Q is estimated to be 1 mega orms. The time resolution of the cavity is expected to be 400 fs when the input RF power is 1 kW and the beam energy is 20 MeV.  
poster icon Poster MOPAB330 [12.920 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB330  
About • paper received ※ 12 May 2021       paper accepted ※ 08 June 2021       issue date ※ 28 August 2021  
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MOPAB331 Design Consideration of a Longitudinal Kicker Cavity for Compensating Transient Beam Loading Effect in Synchrotron Light Sources 1027
 
  • D. Naito, S. Sakanaka, T. Takahashi, N. Yamamoto
    KEK, Ibaraki, Japan
  • T. Yamaguchi
    Sokendai, Ibaraki, Japan
  
  In ultra-low-emittance synchrotron light sources, bunch-lengthening using the combination of main and harmonic cavities is limited by the transient beam-loading (TBL) effect which is caused by gaps in the fill pattern. To manage this effect, we proposed a TBL compensation technique using a wide-band longitudinal kicker cavity*. In the future KEK-LS storage ring, for example, the kicker cavity should provide a compensation voltage of 50 kV with a -3dB bandwidth (BW) of about 5 MHz, as well as its higher-order modes (HOM) should be damped sufficiently. In this presentation, we report our conceptual design of the kicker cavity. We employed the single-mode (SM) cavity concept so that harmful HOMs are dumped by rf absorbers on the beam pipes. The distinctive feature of the SM cavity is its simple structure since it has no HOM damper on the cavity. Another feature is its low R/Q by which the TBL effect in the kicker cavity itself can be reduced significantly. We employed a frequency of 1.5 GHz (third-harmonic) and R/Q of 60 orms through optimizations. Using this kicker cavity with a double rf system, a bunch lengthening by a factor of 4.3 (i.e., 40.9 ps) is expected for the KEK-LS case.
* N.Yamamoto et al., Phys. Rrev. Acc. Beams 21, 012001 (2018) 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB331  
About • paper received ※ 19 May 2021       paper accepted ※ 11 June 2021       issue date ※ 01 September 2021  
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MOPAB332 Design of 4th Harmonic RF Cavities for ESRF-EBS 1031
 
  • A. D’Elia, J. Jacob, V. Serrière, X.W. Zhu
    ESRF, Grenoble, France
  
  Funding: European Union’s Horizon 2020 research and innovation program under grant #871072
An active 4th harmonic RF system for bunch lengthening is under study at the ESRF to improve the performance of the new EBS storage ring, mainly for few bunch operation with high currents per bunch, by reducing Touschek and intrabeam scattering, thereby increasing the lifetime and limiting the emittance growth. It will also reduce impedance heating of the vacuum chambers. The 4th Harmonic 1.41 GHz normal conducting cavity design takes inspiration from the KEK idea of using a TM020 mode exhibiting a reduced R/Q but a higher unloaded Q with respect to TM010. We propose to use multicell cavities for their compactness, the reduced number of required ancillaries and the ease of control for a reduced number of cavities. The drawback is the complexity of the model and the necessity to damp the lower order TM010 mode (LOM) as well as the higher order modes (HOM). The RF design of a 4th harmonic multicell damped cavity will be presented. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB332  
About • paper received ※ 19 May 2021       paper accepted ※ 17 August 2021       issue date ※ 16 August 2021  
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MOPAB333 ESRF-EBS 352 MHz HOM Damped RF Cavities 1034
 
  • A. D’Elia, J. Jacob, V. Serrière
    ESRF, Grenoble, France
  
  For the new ESRF-EBS Storage Ring (SR), HOM damped RF cavities were needed to cope with the reduced thresholds for Longitudinal Coupled Bunch Instabilities (LCBI). The 352 MHz cavities were designed at the ESRF based on an improved version of the 500 MHz EU/ALBA/BESSY structures. A short description of the cavity design will be presented as well as an overview of the fabrication, the preparation and the performance of 13 such cavities for the ESRF-EBS SR. A study of the impedance of a whole cavity equipped with its ancillaries (HOM absorbers, ion pump and tuner) will be presented. One of the three HOM absorbers, the smaller one on top of the cavity, was finally not installed on the machine. The reasons and a detailed analysis in terms of HOM impedances that justifies this choice will be reported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB333  
About • paper received ※ 19 May 2021       paper accepted ※ 07 June 2021       issue date ※ 02 September 2021  
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MOPAB334 Status and Recent Development of FAIR Ring RF Systems 1037
 
  • U. Laier, R. Balß, C. Christoph, M. Frey, P. Hülsmann, H. Klingbeil, H.G. König, D.E.M. Lens, J.S. Schmidt, A. Stuhl, K.G. Thomin, T. Winnefeld
    GSI, Darmstadt, Germany
  • H. Klingbeil
    TEMF, TU Darmstadt, Darmstadt, Germany
  
  Funding: GSI Helmholtzzentrum für Schwerionenforschung GmbH
Five different Ring RF Systems are required for the operation of FAIR (Facility for Antiproton and Ion Research). These systems have to operate at frequencies between 310 kHz and 3.2 MHz, with gap voltages up to 40 kVp and duty cycles from 5·10-4 up to cw. All systems will be realized using inductively loaded (ferrite or magnetic alloy) cavities driven by tetrode-based amplifiers fed by switch-mode power supplies. To stabilize the amplitude, resonance frequency and phase, versatile digital feedback and feedforward control will be used. This contribution will present the latest development on the power part and the LLRF of the four RF systems of the SIS100 (SIS100 Acceleration, SIS100 Bunch Compression, SIS100 Barrier Bucket and SIS100 Longitudinal Feedback) as well as the CR Debuncher system which is part of the Collector Ring. The progress of these systems varies by a large degree. This note will give an overview regarding the status of the design, procurement, realization, testing, optimization, commissioning and preparation for installation of these RF systems. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB334  
About • paper received ※ 18 May 2021       paper accepted ※ 07 June 2021       issue date ※ 12 August 2021  
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MOPAB335 SNS Warm Linac Circulator Breakdown Considerations for the PPU Project 1041
 
  • G.D. Toby, Y.W. Kang, S.-H. Kim, S.W. Lee, J.S. Moss
    ORNL, Oak Ridge, Tennessee, USA
  
  Funding: * This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC05-00OR22725.
Multipacting in accelerating structures is a complex phenomenon about which there is much to be understood. While multipacting research efforts have primarily been focused on superconducting radio frequency (SRF) systems, normal conducting accelerating structures which have a higher thermal capacity, and a greater vacuum pressure tolerance could benefit from additional investigation. This research details multipacting simulation methods and the results of 3-D electromagnetic simulations of RF vacuum windows used on normal conducting linac (NCL) cavities. Benchmarking of the peak electric fields in these structures, benefits of material processing and possible techniques for reducing or eliminating multipacting activities are discussed. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB335  
About • paper received ※ 17 May 2021       paper accepted ※ 28 May 2021       issue date ※ 23 August 2021  
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MOPAB336 Multipacting Analysis of Warm Linac RF Vacuum Windows 1044
 
  • G.D. Toby, Y.W. Kang, S.-H. Kim, S.W. Lee, J.S. Moss
    ORNL, Oak Ridge, Tennessee, USA
  
  Funding: * This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC05-00OR22725.
Multipacting in accelerating structures is a complex phenomenon with which there is much to be understood. While multipacting research efforts have primarily been focused on superconducting radio frequency (SRF) systems, normal conducting accelerating structures that have a higher thermal capacity and a greater vacuum pressure tolerance could benefit from additional investigation. This research details multipacting simulation methods and the results of 3-D electromagnetic simulations of RF vacuum windows used on normal conducting linac (NCL) cavities. Possible techniques for reducing and eliminating multipacting activities in these structures are discussed. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB336  
About • paper received ※ 17 May 2021       paper accepted ※ 28 May 2021       issue date ※ 29 August 2021  
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MOPAB337 Design Study of the Spiral Buncher Cavities for the High Current Injector at IUAC 1048
 
  • S. Kedia, R. Ahuja, R. Mehta, C.P. Safvan
    IUAC, New Delhi, India
  
  Two high energy beam transport (HEBT) cavities have been designed to provide the longitudinal beam bunching between drift tube linac and superconducting super-buncher of the superconducting linear (SC-LINAC) accelerator. The spiral type cavities were chosen over standard quarter wave-type geometry due to its higher shunt impedance. The TRACE-3D ion-optical codes have been used to determine the bunching voltage and physical location of the cavities. The two-gap RF cavity requires 80 kV/gap to provide the longitudinal beam bunching at the entrance of the superconducting buncher. The CST-MWS simulations were performed to design the spiral type bunching cavities. The various parameters including shunt impedance, quality factor, average accelerating field, and total power loss were determined using CST-MWS simulations. The ratio of drift tube radius to the gap was optimized to achieve the maximum effective electric field with minimum field penetration within the gap. The SolidWorks software has been used to prepare a mechanical model for the fabrication.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB337  
About • paper received ※ 15 May 2021       paper accepted ※ 26 May 2021       issue date ※ 26 August 2021  
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MOPAB339 Design Of An X-band 3MeV Standing-wave Accelerating Structure with Nose-cone Structure Made From Two Halves 1051
 
  • F. Liu, H.B. Chen, J. Shi, C.-X. Tang, H. Zha
    TUB, Beijing, People’s Republic of China
  
  This work presents an X-band 3MeV standing-wave accelerating structure with nose cones made from two halves. Milling two longitudinally split halves is one economic method to manufacture accelerating structure for decrease of welding, with increasing the difficulty in machining. This linear accelerator includes 4 buncher cavities and 4 accelerating cavities, and nose cone is applied to achieve high shunt impedance. A technical prototype is under fabrication to bring two milled halves manufacture way into practical application.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB339  
About • paper received ※ 19 May 2021       paper accepted ※ 26 May 2021       issue date ※ 15 August 2021  
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MOPAB340 Experimental Tests with the First Segment of ESS-Bilbao RFQ Linac 1054
 
  • J.L. Muñoz, I. Bustinduy, A. Conde, N. Garmendia, P.J. González, J. Martin, A. Zugazaga
    ESS Bilbao, Zamudio, Spain
  
  The ESS-Bilbao RFQ is an assembly of four segments, each one about 800 mm in length. The first segment has been manufactured before the others, so it could be thoroughly tested in order to validate the chosen technological approach for the RFQ, as it uses polymeric vacuum gaskets and bolts instead of brazing. In this paper we report on the tests run with the segment and their results. Vacuum tests, metrology measurements, low power RF tests as well as extensive tuning tests measuring the cavity resonant quadrupolar frequency as a function of cooling water temperature have been done. Experimental results are compared to the expected values obtained from numerical simulations. We describe the experimental set-ups for the measurements and the simulations. Results are analyzed with the aim of validating the design, and also to provide predictions for tuning and operation of the whole RFQ. As a consequence of the positive results of the tests reported here, the remaining segments have already been tendered.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB340  
About • paper received ※ 19 May 2021       paper accepted ※ 25 May 2021       issue date ※ 20 August 2021  
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MOPAB341 First C-Band High Gradient Cavity Testing Results at LANL 1057
 
  • E.I. Simakov, R.L. Fleming, D. Gorelov, T.A. Jankowski, M.F. Kirshner, J.W. Lewellen, J.D. Pizzolatto, M.E. Schneider, T. Tajima
    LANL, Los Alamos, New Mexico, USA
  • X. Lu, E.A. Nanni, S.G. Tantawi
    SLAC, Menlo Park, California, USA
  • M.E. Middendorf
    ANL, Lemont, Illinois, USA
  
  Funding: Los Alamos National Laboratory LDRD Program.
This poster will report the results of high gradient testing of the two proton β=0.5 C-band accelerating cavities. The cavities for proton acceleration were fabricated at SLAC and tested at high gradient C-band accelerator test stand at LANL. One cavity was made of copper, and the second was made of a copper-silver alloy. LANL test stand was constructed around a 50 MW, 5.712 GHz Canon klystron and is capable to provide power for conditioning single cell accelerating cavities for operation at surface electric fields up to 300 MV/m. These β=0.5 C-band cavities were the first two cavities tested on LANL C-band test stand. The presentation will report achieved gradients, breakdown probabilities, and other characteristics measured during the high power operation. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB341  
About • paper received ※ 19 May 2021       paper accepted ※ 25 May 2021       issue date ※ 30 August 2021  
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MOPAB342 Design, Fabrication, and Commissioning of the Mode Launchers for High Gradient C-Band Cavity Testing at LANL 1060
 
  • E.I. Simakov, J.E. Acosta, D. Gorelov, M.F. Kirshner, J.W. Lewellen
    LANL, Los Alamos, New Mexico, USA
  • P. Borchard
    Dymenso LLC, San Francisco, USA
  • M.E. Schneider
    MSU, East Lansing, Michigan, USA
  
  Funding: Los Alamos National Laboratory LDRD Program.
This poster will report on the design, fabrication, and operation status of the new high gradient C-band TM01 mode launchers for the high gradient C-band test stand at LANL. Modern applications require accelerators with optimized cost of construction and operation, naturally calling for high-gradient acceleration. At LANL we commissioned a test stand powered by a 50 MW, 5.712 GHz Canon klystron. The test is capable of conditioning single cell accelerating cavities for operation at surface electric fields up to 300 MV/m. The rf field is coupled into the cavity from a WR187 waveguide through a mode launcher that converts the fundamental mode of the rectangular waveguide into the TM01 mode of the circular waveguide. Several designs for mode launchers were considered and the final design was chosen based on a compromise between the field enhancements, bandwidth, and simplicity and cost of fabrication. Four mode launchers were fabricated and cold-tested. Two mode launchers with the best transmission characteristics were installed and conditioned to high power. The presentation will report achieved gradients, breakdown probabilities, and other characteristics measured during operation. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB342  
About • paper received ※ 19 May 2021       paper accepted ※ 25 May 2021       issue date ※ 19 August 2021  
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MOPAB343 Optimization of the Parasitic-Mode Damping on the 1.5 GHz TM020-type Harmonic Cavity 1064
 
  • T. Yamaguchi
    Sokendai, Ibaraki, Japan
  • D. Naito, S. Sakanaka, T. Takahashi, N. Yamamoto
    KEK, Ibaraki, Japan
  
  Bunch-lengthening harmonic cavity is one of the essential tools to mitigate the intrabeam scattering in the 4th-generation synchrotron light sources. For this purpose, we proposed a normal-conducting 1.5 GHz harmonic cavity* of TM020-type**. Thanks to its low R/Q (68 ohms) and high unloaded Q (34, 000), bunch gap transient in the harmonic cavity can be reduced to ~20% as compared to that in a typical TM010 cavity. Furthermore, harmful parasitic modes in this cavity can be heavily damped by installing ferrites where no magnetic fields of TM020-mode exist. However, some of the parasitic modes, e.g. TM021 and TM120 modes, are difficult to damp because their field patterns are similar to that of the TM020 mode. To damp such modes effectively, we optimized the cavity inner shape by tailoring the curvature at the cavity equator, the shape of the nose cones, and introducing "bumps" on the inner wall. Our goals of the coupling impedances are fxR < 2.4[kohm GHz] and RT < 23 kohm/m in the longitudinal and the transverse planes, respectively. As a result of optimization, we almost achieved these goals. To confirm our simulation results, fabrication of a low-power test cavity is in progress.
* N . Yamamoto et al., Phys. Rev. Acc. Beams 21, 012001 (2018).
** H. Ego et al., Proc. of the 11th Annual Meeting of Particle Accelerator Society of Japan (PASJ2014), MOOL14 (2014).
 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB343  
About • paper received ※ 19 May 2021       paper accepted ※ 26 May 2021       issue date ※ 01 September 2021  
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MOPAB344 Machine Learning Models for Breakdown Prediction in RF Cavities for Accelerators 1068
 
  • C. Obermair, A. Apollonio, T. Cartier-Michaud, N. Catalán Lasheras, L. Felsberger, W.L. Millar, W. Wuensch
    CERN, Geneva, Switzerland
  • C. Obermair, F. Pernkopf
    TUG, Graz, Austria
  
  Radio Frequency (RF) breakdowns are one of the most prevalent limits in RF cavities for particle accelerators. During a breakdown, field enhancement associated with small deformations on the cavity surface results in electrical arcs. Such arcs degrade a passing beam and if they occur frequently, they can cause irreparable damage to the RF cavity surface. In this paper, we propose a machine learning approach to predict the occurrence of breakdowns in CERN’s Compact LInear Collider (CLIC) accelerating structures. We discuss state-of-the-art algorithms for data exploration with unsupervised machine learning, breakdown prediction with supervised machine learning, and result validation with Explainable-Artificial Intelligence (Explainable AI). By interpreting the model parameters of various approaches, we go further in addressing opportunities to elucidate the physics of a breakdown and improve accelerator reliability and operation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB344  
About • paper received ※ 20 May 2021       paper accepted ※ 16 July 2021       issue date ※ 11 August 2021  
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MOPAB346 Broadband Frequency Electromagnetic Characterisation of Coating Materials 1076
 
  • A. Passarelli, C. Koral, M.R. Masullo
    INFN-Napoli, Napoli, Italy
  • A. Andreone
    Naples University Federico II, Napoli, Italy
  • M. De Stefano
    University of Naples, Naples, Italy
  • V.G. Vaccaro
    Naples University Federico II and INFN, Napoli, Italy
  
  In the new generation of particle accelerators and storage rings, collective effects have to be carefully analyzed. In particular, the finite conductivity of the beam pipe walls is a major source of impedance and instabilities. A reliable electromagnetic (EM) characterisation of different coating materials is required up to hundreds of GHz due to very short bunches. We propose two different measurement techniques for an extended frequency characterization: (i) a THz time domain setup based on the signal transmission response of a tailored waveguide to infer the coating EM properties from 100 to 300 GHz or even further*.**. This technique has been tested both on NEG and amorphous Carbon films. (ii) a resonant method, based on dielectric cavities, to evaluate the surface resistance Rs of thin conducting samples at low (GHz) frequencies***. Due to its high sensitivity, Rs values can be obtained for very thin (nanometric) coatings or for copper samples with a laser treated surface, since they have an expected conductivity very close to bulk copper.
*A. Passarelli et al., Phys. Rev. Accel. Beams, v.21, p.103101, 2018
**A. Passarelli et al., Cond. Matter, v.5, p.9, 2020
***A. Andreone et al., Applied Physics Letters, v.91, n.7, p.072512, 2007
 		 
poster icon Poster MOPAB346 [2.613 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB346  
About • paper received ※ 18 May 2021       paper accepted ※ 09 June 2021       issue date ※ 26 August 2021  
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MOPAB347 High Power Coupler Conditioning for bERLinPro Energy Recovery Linac Injector 1080
 
  • A. Neumann, W. Anders, F. Göbel, A. Heugel, S. Klauke, J. Knobloch, M. Schuster, Y. Tamashevich
    HZB, Berlin, Germany
  
  Funding: The work is funded by the Helmholtz-Association, BMBF, the state of Berlin and HZB.
Helmholtz Zentrum Berlin is currently finalizing the construction of the demonstrator Energy Recovery Linac bERLinPro *. The first part, which will be commissioned, will be the injector consisting of a superconducting RF (SRF) photo-injector (Gun) and a Booster module made up of three two cell SRF cavities. For the latter the 2.3 MeV beam from the gun needs to be accelerated to 6.5 MeV, whereas one Booster cavity will be operated in zero-crossing mode for bunch-shortening. Thus, for the final stage with a 100 mA beam, the twin power couplers of the Booster cavity need to deliver up to 120 kW in travelling continous wave (CW) mode at 1.3 GHz each. To achieve that, a dedicated coupler conditioning setup was installed and commissioned. Here, we will present the first conditioning results with the bERLinPro Booster fundamental power couplers in pulsed and CW regime.
* M. Abo-Bakr et al., in Proc. 9th Int. Particle Accelerator Conf. (IPAC’18), Vancouver, BC, Canada, Apr. 4,, pp. 4127-4130, doi:10.18429/JACoW-IPAC2018-THPMF034 		 
poster icon Poster MOPAB347 [3.256 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB347  
About • paper received ※ 18 May 2021       paper accepted ※ 08 June 2021       issue date ※ 14 August 2021  
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MOPAB348 Portable 2.5 MeV X-Band Linear Accelerator Structure 1084
 
  • A.V. Mishin, K. Brown, M. Denney, D. Fischer, N.P. Hanson, S. Proskin, J. Stammetti
    Varex Imaging, Salt Lake City, USA
  
  Two versions of 2.5 MeV X-Band linear accelerator structure have been designed and tested. The first is a traditional single input linac, and the other one is a dual input, two section linac with power input through a 3 dB coupler. The linac is designed for a portable linac system, which can be used for security screening, non-destructive testing, medical and industrial CT, and, perhaps, some other applications.  
poster icon Poster MOPAB348 [1.490 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB348  
About • paper received ※ 15 May 2021       paper accepted ※ 28 May 2021       issue date ※ 23 August 2021  
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MOPAB350 RF Buncher Cavity for Polarized He-3 Beam at BNL 1090
 
  • T. Kanesue, S.M. Trabocchi
    BNL, Upton, New York, USA
  • A. Murata
    TIT, Tokyo, Japan
  
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
A 100.625 MHz quarter wave resonator type rf buncher cavity was fabricated for polarized He-3 spin rotator beam line at BNL. This cavity will be installed in the existing EBIS-To-Booster beam line to provide effective voltage of more than 40 kV for 2 MeV/u 3He2+ beam. This cavity has a large drift tube inner diameter of 80 mm and small gap length of 5 mm. The buncher consists of 3 sections, which are a cavity main body including drift tube, stem, and inner wall, a lid with a power coupler, and a lid with an inductive tuner. The main body was machined from a bulk copper only by CNC machining. The result of low power test agreed well with rf simulation without any alignment. The difference between measured and calculated resonant frequency was <0.1 %, and measured Q value was 92 % of that in simulation. The cavity rf design and test results will be shown. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB350  
About • paper received ※ 26 May 2021       paper accepted ※ 28 May 2021       issue date ※ 12 August 2021  
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MOPAB351 Using an RFQ to Transport Intense Heavy Ion Beams from an ECR Ion Source 1093
 
  • G.O. Rodrigues
    IUAC, New Delhi, India
  • R.W. Hamm
    R&M Technical Enterprises, Pleasanton, California, USA
  
  In the transport of high intensity, heavy ions from an ECR ion source through a low energy beam transport (LEBT) section, space charge can limit the transmission. It has been proposed to use a Radio Frequency Quadrupole (RFQ) to efficiently address this problem. The stray magnetic field of the ECR ion source can be used to provide focusing against the space charge blow-up when using the Direct Plasma Injection Scheme (DPIS) developed for laser ion sources. The RFQ will focus and transport the injected beam, eliminating most of the charge states extracted from the ECR ion source. This narrowing of the charge state distribution is a filter, reducing the low energy beam transport problem, as well as the emittance growth for the desired beam. A combined extraction/matching system has been designed for direct injection into a 48.5 MHz RFQ for the production of 238U40+ (0.52 mA) and 209Bi30+ (1.047 mA) beams. The IGUN code has been used to design the injection directly into the RFQ. The RFQ design has been modified with a pre-buncher built into the vanes to narrow the transmitted charge state distribution as much as possible. The design details of this system will be presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB351  
About • paper received ※ 20 May 2021       paper accepted ※ 17 August 2021       issue date ※ 15 August 2021  
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MOPAB352 High Power Test of a Dielectric Disk Loaded Accelerator for a Two Beam Wakefield Accelerator 1096
 
  • B.T. Freemire, C.-J. Jing, S. Poddar
    Euclid Beamlabs, Bolingbrook, USA
  • M.E. Conde, D.S. Doran, G. Ha, W. Liu, J.G. Power, J.H. Shao, C. Whiteford, E.E. Wisniewski
    ANL, Lemont, Illinois, USA
  • M.M. Peng
    TUB, Beijing, People’s Republic of China
  • E.E. Wisniewski
    Illinois Institute of Technology, Chicago, Illinois, USA
  • Y. Zhao
    Euclid TechLabs, Solon, Ohio, USA
  
  Funding: Small Business Innovation Research Contract No. DE-SC0019864 U.S. DOE Office of Science Contract No. DE-AC02-06CH11357
As part of the Argonne 500 MeV short pulse Two Beam Wakefield Acceleration Demonstrator, a single cell X-band dielectric disk loaded accelerator (DDA) has been designed, fabricated, and tested at high power at the Argonne Wakefield Accelerator. The DDA should provide a short pulse (~20 ns) high gradient (>300 MV/m) accelerator while maintaining a reasonable r/Q and high group velocity. This will allow a significantly larger RF-to-beam efficiency than is currently possible for conventional accelerating structures. A low loss barium titantate ceramic, µr = 50, was selected, and a low temperature brazing alloy chosen to preserve the dielectric properties of the ceramic during brazing. High power testing produced breakdown at the triple junction, resulting from the braze joint design. No evidence of breakdown was observed on the iris of the disk, indicating that the maximum surface electric field on the dielectric was not reached. An improved braze joint has been designed and is in production, with high power testing to follow. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB352  
About • paper received ※ 19 May 2021       paper accepted ※ 08 June 2021       issue date ※ 21 August 2021  
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MOPAB353 Design of a compact Ka-Band Mode Launcher for High-gradient Accelerators 1100
 
  • G. Torrisi, G.S. Mauro, G. Sorbello
    INFN/LNS, Catania, Italy
  • M. Behtouei, L. Faillace, B. Spataro, A. Variola
    INFN/LNF, Frascati, Italy
  • V.A. Dolgashev
    SLAC, Menlo Park, California, USA
  • L. Faillace, M. Migliorati
    Sapienza University of Rome, Rome, Italy
  • M. Migliorati
    INFN-Roma1, Rome, Italy
  • J.B. Rosenzweig
    UCLA, Los Angeles, California, USA
  • G. Sorbello
    University of Catania, Catania, Italy
  
  In this work, we present the RF design of a table-top Ka-Band mode launcher operating at 35.98 GHz. The structure consists of a symmetrical 4-port WR28 rectangular-TE10-to-circular-TM01 mode converter that is used to couple a peak output RF power of 5 MW (pulse length up to 50 ns and repetition rate up to 100 Hz) in Ka-Band linear accelerator able to achieve very high accelerating gradients (up to 200 MV/m). Numerical simulations have been carried out with the 3D full-wave commercial simulator Ansys HFSS in order to obtain a preliminary tuning of the accelerating field flatness at the operating frequency f0=35.98 GHz. The main RF parameters, such as reflection coefficient, transmission losses, and conversion efficiency are given together with a verification of the field azimuthal symmetry which avoids dipole and quadrupole deflecting modes. To simplify future manufacturing, reduce fabrication costs, and also reduce the probability of RF breakdown, the proposed new geometry has "open" configuration. This geometry eliminates the flow of RF currents through critical joints and allows this device to be milled from metal blocks.  
poster icon Poster MOPAB353 [3.131 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB353  
About • paper received ※ 19 May 2021       paper accepted ※ 09 June 2021       issue date ※ 27 August 2021  
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MOPAB355 Multi-Objective Optimization of RF Structures 1103
 
  • S.J. Smith, R. Apsimon, G. Burt, M.J.W. Southerby
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • S. Setiniyaz
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • S. Setiniyaz
    Lancaster University, Lancaster, United Kingdom
  
  In this work, we apply multi-objective optimization methods to single-cell cavity models generated using non-uniform rational basis splines (NURBS). This modeling method uses control points and a NURBS to generate the cavity geometry, which allows for greater flexibility in the shape, leading to improved performance. Using this approach and multi-objective genetic algorithms (MOGAs) we find the Pareto frontiers for the typical key quantities of interest (QoI) including peak fields, shunt impedance and the modified Poynting vector. Visualizing these results becomes increasingly more difficult as the number of objectives increases, therefore, in order to understand these frontiers, we provide several techniques for analyzing, visualizing and using multi-dimensional Pareto fronts specifically for RF cavity design.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB355  
About • paper received ※ 19 May 2021       paper accepted ※ 15 July 2021       issue date ※ 30 August 2021  
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MOPAB356 The ESS MEBT RF Buncher Cavities Conditioning Process 1107
 
  • I. Bustinduy, N. Garmendia, P.J. González, A. Kaftoosian, S. Masa, I. Mazkiaran, L.C. Medina, J.L. Muñoz
    ESS Bilbao, Zamudio, Spain
  • J. Etxeberria, J.P.S. Martins
    ESS, Lund, Sweden
  
  Funding: This work is part of FEDER-TRACKS project, co-funded by the European Regional Development Fund (ERDF) .
As part of the 5 MW European Spallation Source (ESS), the Medium Energy Beam Transport (MEBT) was designed, assembled, and installed in the tunnel since May 2020 by ESS-Bilbao. This section of the accelerator is located between the Radio Frequency Quadrupole (RFQ) and the Drift Tube Linac (DTL). The main purpose of the MEBT is to match the incoming beam from the RFQ both transversely and longitudinally into the DTL. The longitudinal matching is achieved by three 352.209 MHz RF buncher cavities. In this paper, we focus on the RF conditioning process for each set of power coupler and buncher cavity. For this purpose, different tools were developed on EPICS and Python as well as electronics hardware such as Fast Interlock Module (FIM) and timing system. These tools served to automatize both the cavity frequency tuning and the power ramp-up process and will be described in detail in the following sections. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB356  
About • paper received ※ 18 May 2021       paper accepted ※ 09 June 2021       issue date ※ 25 August 2021  
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MOPAB357 The New Design of the RF System for the SPS-II Light Source 1110
 
  • N. Juntong, T. Chanwattana, S. Chunjarean, S. Krainara, T. Phimsen, T. Pulampong
    SLRI, Nakhon Ratchasima, Thailand
  • K. Manasatitpong
    Synchrotron Light Research Institute (SLRI), Muang District, Thailand
  
  The new light source facility in Thailand, SPS-II, is a ring-based 3 GeV light source with a circumference of approximately 330 m. The target stored beam current is 300 mA with an emittance of below 1.0 nm rad. The injector has been changed from a full energy linac to a booster injector with 150 MeV linac. The main RF frequency has been reconsidered to a low-frequency range at 119 MHz. Low frequency is chosen with the benefit of low RF voltage for a high RF acceptance together with experience with the present ring RF system of 118 MHz. Details of RF frequency consideration will be discussed. The requirements and details of the RF systems in the booster ring and the storage ring will be presented.  
poster icon Poster MOPAB357 [1.696 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB357  
About • paper received ※ 17 May 2021       paper accepted ※ 08 June 2021       issue date ※ 14 August 2021  
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MOPAB358 Design and Measurement of the 1.4 GHz Cavity for LEReC Linac 1113
 
  • B.P. Xiao, J.C. Brutus, J.M. Fite, K. Hamdi, D. Holmes, K. Mernick, K.S. Smith, J.E. Tuozzolo, T. Xin, A. Zaltsman
    BNL, Upton, New York, USA
  
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
The Low Energy RHIC electron Cooler (LEReC) is the first electron cooler based on rf acceleration of electron bunches. To further improve RHIC luminosity for heavy ion beam energies below 10 GeV/nucleon, a normal conducting RF cavity at 1.4 GHz was designed and fabricated for the LINAC that will provide longer electron bunches for the LEReC. It is a single-cell cavity with an effective cavity length shorter than half of the 1.4 GHz wavelength. This cavity was fabricated and tested on-site at BNL to verify RF properties, i.e. the resonance frequency, FPC coupling strength, tuner system performance, and high power tests. In this paper, we report the RF test results for this cavity. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB358  
About • paper received ※ 17 May 2021       paper accepted ※ 25 June 2021       issue date ※ 24 August 2021  
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MOPAB359 Operational Experience and Redesign of the Tuner without Spring Fingers for the LEReC Warm Cavity 1116
 
  • B.P. Xiao, J.M. Brennan, J.C. Brutus, K. Mernick, S. Polizzo, S.K. Seberg, F. Severino, K.S. Smith, A. Zaltsman
    BNL, Upton, New York, USA
  
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
A folded coaxial tuner without spring fingers was designed for the Low Energy RHIC electron Cooler (LEReC) 2.1 GHz warm cavity. During RHIC run 2019, this tuner was found to cause cavity trips via different failure modes. After analyzing these failure modes, a new straight coaxial tuner without spring fingers was proposed and was installed. We show the operational experience of the new tuner in this paper. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB359  
About • paper received ※ 17 May 2021       paper accepted ※ 25 June 2021       issue date ※ 29 August 2021  
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MOPAB361 Threshold in Filling Failure of RF Cavity Caused by Beam Loading in Multipactor 1122
 
  • J. Pang
    USTC/NSRL, Hefei, Anhui, People’s Republic of China
  • Y. Dong
    Institute of Applied Physics and Computational Mathematics, People’s Republic of China
  • Y. Du
    Institute of Fluid Physics,, China Academy of Engineering Physics, Mianyang, People’s Republic of China
  
  Funding: NSFC
A pulsed RF cavity would be heavily detuned caused by beam loading of multipactor current in the RF filling process. Multipactor zone would be expended by several times than that in static states with assumptions of fixed voltage and no beam loading. The dynamic of multipactor in the RF filling process was simulated by coupling with parameters of external circuit with the developed simulation code, and test in experiments with a parallel-plate resonator. Threshold of RF voltage, which means the lower boundary of peak voltage of multipactor zone, had been quantified with different cavity parameters. When we increased the gap length, the measured threshold became larger due to the ionization in background gas. Then the secondary emission factor would be increased in simulation for consistence with the experiment results. Additionally, some multipactor phenomenon could not be predicted precisely because the simulation code did not take account of ionization. The hysteresis of phase and energy of ionization electrons would be a new driving factor for the growth of multipactor in certain conditions. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB361  
About • paper received ※ 19 May 2021       paper accepted ※ 24 May 2021       issue date ※ 10 August 2021  
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MOPAB362 Atomistic Modeling of the Coupling Between Electric Fields and Bulk Plastic Deformation in Rf Structures 1125
 
  • S. Bagchi, D. Perez
    LANL, Los Alamos, New Mexico, USA
  
  Funding: LANL-LDRD
A notable bottleneck in achieving high-gradient RF technology is dictated by the onset of RF breakdown. While bulk mechanical properties are known to significantly affect breakdown propensity, the underlying mechanisms coupling RF fields to bulk plastic deformation in experimentally relevant thermo-electrical loading conditions remain to be identified at the atomic scale. Here, we present results of large-scale molecular dynamics simulations (MD) to investigate possible modes of coupling. We consider the activation of Frank-Read (FR) sources, which leads to dislocation multiplication, under the action of bi-axial thermal stresses and surface electric-field. With a charge-equilibration formalism incorporated in a classical MD model, we show that a surface electric field acting on an either preexisting or dislocation-induced surface step, can generate a long-range resolved shear stress field inside the bulk of the sample. We investigate the feedback between step growth following dislocation emission and subsequent activations of FR sources and discuss the regimes of critical length-scales and densities of dislocations, where such a mechanism could promote RF breakdown precursors. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB362  
About • paper received ※ 19 May 2021       paper accepted ※ 10 June 2021       issue date ※ 19 August 2021  
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MOPAB363 Design, Characteristics and Dynamic Properties of Mobile Plunger-based Frequency Tuning System for Coaxial Half Wave Resonators 1129
 
  • D. Bychanok, S. Huseu, S.A. Maksimenko, A.E. Sukhotski
    INP BSU, Minsk, Belarus
  • A.V. Butenko, E. Syresin
    JINR, Dubna, Moscow Region, Russia
  • M. Gusarova, M.V. Lalayan, S.M. Polozov
    MEPhI, Moscow, Russia
  • V.S. Petrakovsky, A.I. Pokrovsky, A. Shvedov, S.V. Yurevich
    Physical-Technical Institute of the National Academy of Sciences of Belarus, Minsk, Belarus
  • Y. Tamashevich
    HZB, Berlin, Germany
  
  The practical realization of a prototype of the frequency tuning system (FTS) for coaxial half-wave cavities (HWR) for the Nuclotron-based Ion Collider fAcility (NICA) injector is presented. The impact of FTS on electromagnetic parameters of copper HWR prototype is experimentally studied and discussed. The most important parameters like tuning range, tuning sensitivity, the dependence of the resonant frequency on the position of the plungers are estimated. The effective operation algorithms of the proposed FTS are discussed and analyzed. The dynamic characteristics of FTS are investigated and showed the ability to adjust the frequency with an accuracy of about 70 Hz.  
poster icon Poster MOPAB363 [3.597 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB363  
About • paper received ※ 18 May 2021       paper accepted ※ 09 June 2021       issue date ※ 11 August 2021  
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MOPAB364 Shielded Pair Method for Cylindrical Surface Resistance Measurement at Cryogenic Temperature 1132
 
  • K. Brunner, S. Calatroni, F. Caspers
    CERN, Geneva, Switzerland
  • D. Barna
    Wigner Research Centre for Physics, Institute for Particle and Nuclear Physics, Budapest, Hungary
  
  The shielded pair resonator method was already used in the past at CERN to measure the surface resistivity of the LHC beam screen both at room temperature and cryogenic temperature. We have refined and adapted the measurement to be able to measure other types of beam screens and also to operate in a strong dipolar magnetic field. This is necessary for testing the properties of HTS coated beam screens or the possible effects of coatings and surface treatments for e-cloud suppression. Several calibration runs were done at cryogenic temperatures (4.2 K) measuring the surface resistivity of a copper pipe to identify the precision, stability and reproducibility achievable using this method. This work describes the challenges of the measurement and ways to mitigate them.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB364  
About • paper received ※ 17 May 2021       paper accepted ※ 22 June 2021       issue date ※ 12 August 2021  
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MOPAB365 Construction and First Test Results of the Barrier and Harmonic RF Systems for the NICA Collider 1136
 
  • A.G. Tribendis, Y.A. Biryuchevsky, K.N. Chernov, A.N. Dranitchnikov, E. Kenzhebulatov, A.A. Kondakov, A.A. Krasnov, Ya.G. Kruchkov, S.A. Krutikhin, G.Y. Kurkin, A.M. Malyshev, A.Yu. Martynovsky, N.V. Mityanina, S.V. Motygin, A.A. Murasev, V.N. Osipov, V.M. Petrov, E. Pyata, E. Rotov, V.V. Tarnetsky, I.A. Zapryagaev, A.A. Zhukov
    BINP SB RAS, Novosibirsk, Russia
  • O.I. Brovko, A.M. Malyshev, I.N. Meshkov, E. Syresin
    JINR, Dubna, Moscow Region, Russia
  • I.N. Meshkov
    Saint Petersburg State University, Saint Petersburg, Russia
  • E. Rotov
    NSU, Novosibirsk, Russia
  • A.G. Tribendis
    NSTU, Novosibirsk, Russia
  • A.V. Zinkevich
    Triada-TV, Novosibirsk, Russia
  
  This paper reports on the design features and construction progress of the three RF systems for the NICA collider being built at JINR, Dubna. Each of the two collider rings has three RF systems named RF1 to 3. RF1 is a barrier bucket system used for particles capturing and accumulation during injection, RF2 and 3 are resonant systems operating at 22nd and 66th harmonics of the revolution frequency and used for the 22 bunches formation. The RF systems are designed and produced by Budker INP. Solid state RF power amplifiers developed by the Triada-TV company, Novosibirsk, are used for driving the RF2 and three cavities. Two RF1 stations were already delivered to JINR, the prototypes of the RF2 and 3 stations were built and successfully tested at BINP. Series production of all eight RF2 and sixteen RF3 stations is in progress. The design modifications and test results are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB365  
About • paper received ※ 18 May 2021       paper accepted ※ 24 May 2021       issue date ※ 14 August 2021  
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MOPAB366 Improving Magnetic Materials for RCS Cavity Tuners 1139
 
  • R.L. Madrak, N.M. Curfman, G.V. Romanov, C.-Y. Tan, I. Terechkine
    Fermilab, Batavia, Illinois, USA
  • G. Das, A.K. Samanta
    Ceramic Magnetics, Inc., National Magnetics Group, Inc., Bethlehem, USA
  
  Funding: United States Department of Energy, Contract No. DE-AC02-07CH11359
Within the Lab Directed R&D Program at Fermilab, and in partnership with National Magnetics, we have recently begun to study and attempt to improve the loss parameter in garnet material. This could be used for fast tuner applications such as in rapid cycling synchrotrons. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB366  
About • paper received ※ 19 May 2021       paper accepted ※ 25 May 2021       issue date ※ 15 August 2021  
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MOPAB370 X-Band RF Spiral Load Optimization for Additive Manufacturing Mass Production 1143
 
  • H. Bursali
    Sapienza University of Rome, Rome, Italy
  • N. Catalán Lasheras, R.L. Gerard, A. Grudiev, O. Gumenyuk, P. Morales Sanchez, B. Riffaud
    CERN, Geneva, Switzerland
  • J. Sauza-Bedolla
    Lancaster University, Lancaster, United Kingdom
  
  The CLIC main linac uses X-band traveling-wave normal conducting accelerating structures. The RF power not used for beam acceleration nor dissipated in the resistive wall is absorbed in two high power RF loads that should be as compact as possible to minimize the total footprint of the machine. In recent years, CERN has designed, fabricated and successfully tested several loads produced by additive manufacturing. With the current design, only one load can be produced in the 3D printing machine at a time. The aim of this study is optimizing the internal cross-section of loads in order to create a stackable design to increase the number of produced parts per manufacturing cycle and thus decrease the unit price. This paper presents the new design with an optimization of the internal vacuum part of the so-called RF spiral load. In this case, RF and mechanical designs were carried out in parallel. The new cross section has showed good RF reflection reaching less than -30 dB in simulations. The final load is now ready to be manufactured and high-power tested. This new load will not only provide cost saving but also faster manufacturing for mass production.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB370  
About • paper received ※ 18 May 2021       paper accepted ※ 26 May 2021       issue date ※ 23 August 2021  
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MOPAB371 A Coupon Tester for Normal Conducting High-Gradient Materials 1147
 
  • J.W. Lewellen, D. Gorelov, D. Perez, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
  • M.E. Schneider
    Michigan State University, East Lansing, Michigan, USA
  
  Funding: Los Alamos National Laboratory LDRD Program
A coupon tester is an RF structure used to subject a material sample to very high RF fields, with the fields on the sample, or coupon, being higher than elsewhere in the cavity. To date, most such cavities were originally intended to explore the RF properties of superconducting materials, and can expose the sample to strong magnetic fields, but weak to no electric fields. As part of a program to develop materials and structures for high-gradient (> 100 MV/m), low-breakdown-rate normal-conducting accelerators, we have designed a C-band (5.712 GHz) cavity intended to subject samples to both magnetic and electric fields comparable to those experienced in high-gradient structure designs, using a TM-mode cavity; the electric and magnetic fields along the sample coupon can be directly compared to the fields on the iris of high-gradient structures. This poster will present the design criteria for our coupon tester cavity, nominal operating parameters, and our structure concept. The cavity design will be refined over the next several months, and will be constructed and in service near the start of 2022. 		 
poster icon Poster MOPAB371 [0.764 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB371  
About • paper received ※ 17 May 2021       paper accepted ※ 26 May 2021       issue date ※ 30 August 2021  
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MOPAB374 Creating Exact Multipolar Fields in Accelerating RF Cavities via an Azimuthally Modulated Design 1154
 
  • L.M. Wroe, S.L. Sheehy
    JAI, Oxford, United Kingdom
  • R. Apsimon
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • M. Dosanjh
    CERN, Meyrin, Switzerland
  • S.L. Sheehy
    The University of Melbourne, Melbourne, Victoria, Australia
  
  In this paper, we present a novel method for designing RF structures with specifically tailored multipolar field contributions. This has a range of applications, including the suppression of unwanted multipolar fields or the introduction of wanted terms, such as for quadrupole focusing. In this article, we outline the general design methodology and compare the expected results to 3D CST simulations.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB374  
About • paper received ※ 19 May 2021       paper accepted ※ 08 June 2021       issue date ※ 23 August 2021  
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TUXC02
 The LCLS-II-HE R&D Program: New Insights into Improving the Performance of Nitrogen-Doped SRF Cavities  
 
  • D. Gonnella, S. Aderhold, J.T. Maniscalco, M.C. Ross
    SLAC, Menlo Park, California, USA
  • D. Bafia, M. Checchin, A. Grassellino, S. Posen
    Fermilab, Batavia, Illinois, USA
  • A.D. Palczewski, C.E. Reece
    JLab, Newport News, Virginia, USA
  
  Funding: US DOE and the LCLS-II-HE Project
Nitrogen doping has now been demonstrated to produce SRF cavities of unprecedented Q0 values when manufactured in an industrial setting. LCLS-II has shown over 300 cavities with an average Q0 of more than 3·1010 at 16 MV/m and represents an overwhelming success of the doping protocol. LCLS-II-HE will add an additional 23 superconducting cryomodules to the LCLS-II linac, requiring cavities to operate at similar levels of high Q0 but at 21 MV/m instead of 16 MV/m. Nitrogen-doped cavities have been historically plagued by lower quench fields than other cavity preparation methods. Therefore, an R&D effort was launched to improve upon the quench fields of doped cavities while maintaining the high Q0. Here we present results on single-cells and 9-cells from new doping recipe pursuits, transfer of these new recipes to cavity vendors, and results on vendor-produced 9-cell cavities. This program has led to the discovery of the importance of the cold electropolish for producing higher quench fields. Finally, we will show results from the first cryomodule produced with these new cavities operating at HE gradients. 		 
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TUPAB076 High-Gradient Breakdown Studies of an X-Band Accelerating Structure Operated in the Reversed Taper Direction 1543
 
  • X.W. Wu, N. Catalán Lasheras, A. Grudiev, G. McMonagle, I. Syratchev, W. Wuensch
    CERN, Meyrin, Switzerland
  • M. Boronat
    IFIC, Valencia, Spain
  • A. Castilla, A.V. Edwards, W.L. Millar
    Lancaster University, Lancaster, United Kingdom
  
  The results of high-gradient tests of a tapered X-band traveling-wave accelerator structure powered in reversed direction are presented. Powering the tapered structure from the small aperture, normally output, at the end of the structure provides unique conditions for the study of gradient limits. This allows high fields in the first cell for a comparatively low input power and a field distribution that rapidly falls off along the length of the structure. A maximum gradient of 130 MV/m in the first cell at a pulse length of 100 ns was reached for an input power of 31.9 MW. Details of the conditioning and operation at high-gradient are presented. Various breakdown rate measurements were conducted at different power levels and rf pulse widths. The structure was standard T24 CLIC test structure and was tested in Xbox-3 at CERN.  
poster icon Poster TUPAB076 [1.077 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB076  
About • paper received ※ 19 May 2021       paper accepted ※ 12 July 2021       issue date ※ 12 August 2021  
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TUPAB077 Novel Open Cavity for Rotating Mode SLED-Type RF Pulse Compressors 1547
 
  • X.W. Wu, A. Grudiev
    CERN, Meyrin, Switzerland
  
  A new X-band high-power rotating mode SLAC Energy Doubler (SLED)-type rf pulse compressor is proposed. It is based on a novel cavity type, a single open bowl-shape energy storage cavity with high Q0 and compact size, which is coupled to the waveguide using a compact rotating mode launcher. The novel cavity type is applied to the rf pulse compression system of the main linac rf module of the klystron-based option of the Compact Linear Collider (CLIC). Quasi-spherical rotating modes of \rm{TE}1,2,4 and \rm{TE}1,2,13 are proposed for the correction cavity and storage cavity of the rf pulse compression system respectively. The storage cavity working at \rm{TE}1,2,13 has a Q0 of 240000 and a diameter less than 33 cm. The design of the pulse compressor and in particular of the high-Q cavity will be presented in detail.  
poster icon Poster TUPAB077 [1.229 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB077  
About • paper received ※ 19 May 2021       paper accepted ※ 10 June 2021       issue date ※ 27 August 2021  
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WEPAB038 Commissioning of a New X-Band, Low-Noise LLRF System 2683
 
  • A.V. Edwards, M. Boronat Arevalo, N. Catalán Lasheras, G. McMonagle
    CERN, Meyrin, Switzerland
  • A.C. Dexter
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  
  To increase beam energy in the CLEAR facility at CERN and study the CLIC accelerating structure prototype in operating conditions, the first X-band test facility at CERN was upgraded in 2020. Both, the acquisition and software systems at X-band test stand 1 (Xbox1) were upgraded to exhibit low phase noise which is relevant to klystron based CLIC and to the use of crab cavities in the beam delivery system. The new LLRF uses down-conversion which necessitates a local oscillator which can be produced by two different methods. The first is a PLL, a commonly used technique which has been previously employed at the other X-band facilities at CERN. The second is a novel application of a single sideband up-convertor. The up-convertor system has demonstrated reduced phase noise when compared with the PLL. The commissioning of the new system began in late 2020 with the conditioning of a 50 MW Klystron. Measurements of the quality of the new LLRF will be shown. These will compare the PLL and up-convertor with particular attention on the quality of the phase measurements. Also, a preliminary study of phase shifts in the waveguide network due to temperature changes will be presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB038  
About • paper received ※ 13 May 2021       paper accepted ※ 05 July 2021       issue date ※ 20 August 2021  
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WEPAB370 Study of an L-Band CW Linac 3575
 
  • J. Gao, H.B. Chen, J.Y. Liu, J. Shi, H. Zha
    TUB, Beijing, People’s Republic of China
  
  We have studied an L-band linac based on a cheap industrial magnetron, which works at CW mode with 75kW averaged output-power. The designed energy-gain of electrons is 500keV. Low accelerating gradient was the dominant problem encountered during the structure design. We adopted a standing-wave structure with magnetically coupling and nose cones to increase the effective shunt impedance. A 7-cell design has been completed, of which the transverse dynamics and thermodynamics were simulated. Results showed that this accelerating structure could work stably at 59 C and 100 mA output beam current was achieved. This L-band design provided a cheap and efficient way to generate low-energy electrons for industrial irradiation processing.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB370  
About • paper received ※ 19 May 2021       paper accepted ※ 21 June 2021       issue date ※ 19 August 2021  
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WEPAB401 Study for Alternative Cavity Wall and Inductive Insert Material 3650
 
  • C.E. Taylor, C.-F. Chen, T.W. Hall, E. Henestroza, J.T.M. Lyles, J. Upadhyay
    LANL, Los Alamos, New Mexico, USA
  • S. Biedron, M.A. Fazio, S.I. Salvador, T.J. Schaub
    UNM-ECE, Albuquerque, USA
  
  Funding: Contract No. 89233218CNA000001, supported by the U.S. Department of Energy’s National Nuclear Security Administration (NNSA), for the management and operation of Los Alamos National Laboratory (LANL).
The goal of this work was to develop a solution to the problem of longitudinal beam instability. Beam instability has been a significant problem with storage rings’ performance for many decades. The proton storage ring (PSR) at the Los Alamos Neutron Science Center (LANCE) is no exception. To mitigate the instability, it was found that ferrite inductive inserts can be used to bunch the protons that are diverging due to the electron background. The PSR was the first storage ring to successfully use inductive inserts to mitigate the longitudinal instability with normal production beams. However, years later new machine upgrades facilitate shorter, more intense beams to meet the needs of researchers. The ferrite inserts used to reduce the transverse instabilities induce a microwave instability with the shorter more intense proton beam. This study investigates alternative magnetic materials for inductive inserts in particle beam storage rings, including the necessary engineering for maintaining the ideal temperature during operation.
’ tjschaub@unm.edu 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB401  
About • paper received ※ 29 May 2021       paper accepted ※ 02 July 2021       issue date ※ 15 August 2021  
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THXC06 Design and Measurements of an X-Band 8 MeV Standing-Wave Electron Accelerator 3744
 
  • F. Liu, H.B. Chen, J. Shi, C.-X. Tang, H. Zha
    TUB, Beijing, People’s Republic of China
  
  X-band low-energy electron linear accelerators are attractive to industrial and medical applications due to the compact size. In this work we present tests of an 8 MeV X-band accelerator for industrial use. It adopts the coaxial coupling standing wave structure working at 9300 MHz. The accelerator length is 50 cm including the cavity, thermal gun, and electron window. Dedicated bunching cells are designed to reduce the energy spread. In the high power tests, the accelerator was able to generate the electron beam with RMS energy spread less than 1% (beam energy: 8.1 MeV, peak current: 45 mA). Combining features of compact size and the low energy spread, this X-band accelerator design is valuable for various applications.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXC06  
About • paper received ※ 19 May 2021       paper accepted ※ 01 July 2021       issue date ※ 02 September 2021  
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THPAB081 High-Power Prototype Canon Coupler for APS-U Booster Cavities 3956
 
  • G.J. Waldschmidt, D.J. Bromberek, D. Horan, G. Trento, U. Wienands
    ANL, Lemont, Illinois, USA
  • T. Harada, H. Oikawa, H. Takahashi
    CETD, Tochigi, Japan
  
  The Advanced Photon Source Upgrade (APS-U) plans to achieve a beam capture efficiency above 90% at 17 nC bunch charge into the Booster. Due to large beam loading at injection, the 352-MHz Booster cavities will be significantly detuned necessitating effective-power handling much greater than the 100kW effective power rating of the present coupler. Canon Electron Tubes & Devices Co., Ltd. (CETD) has designed and built a compact coupler for the APS-U Booster using a high-power ceramic disk window design in addition to accommodating significant space restrictions and additional diagnostics and cooling requirements. The coupler design was modified from an existing 500MHz, 800kW coupler that has been in routine operation at KEKB. The APS-U coupler has been installed and tested in the high-power 352-MHz test stand at the APS. The details of the design and testing of the prototype coupler will be reported in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB081  
About • paper received ※ 18 May 2021       paper accepted ※ 28 July 2021       issue date ※ 15 August 2021  
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THPAB223 Energy Compression System Radio Frequency Design at the Canadian Light Source 4231
 
  • E.J. Ericson, D. Bertwistle, M.J. Boland
    CLS, Saskatoon, Saskatchewan, Canada
  
  The Canadian Light Source (CLS), Canada’s only synchrotron light source, is considering a linear accelerator (LINAC) upgrade. As a result, the radio frequency (RF) structure in the downstream Energy Compression System (ECS) needs to be redesigned. In this paper, we describe the design process followed to determine the geometry of the RF structure cells and coupler.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB223  
About • paper received ※ 18 May 2021       paper accepted ※ 28 July 2021       issue date ※ 28 August 2021  
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THPAB272 Validation of Two Re-Buncher Cavities under High Beam Loading for LIPAc 4343
 
  • D. Gavela, I. Podadera, F. Toral
    CIEMAT, Madrid, Spain
  • I. Moya
    Fusion for Energy, Garching, Germany
  • F. Scantamburlo
    IFMIF/EVEDA, Rokkasho, Japan
  
  Funding: Work partially supported by the Spanish Ministry of Science and Innovation under project AIC-A-2011-0654 and FIS2013-40860-R
Two re-buncher cavities were installed at the Medium Energy Beam Transport line of the LIPAc accelerator, presently being commissioned at Rokkasho (Japan). They are IH-type cavities with five gaps providing an effective voltage of 350 kV at 175 MHz for a nominal operation of 125 mA CW deuterons at 5 MeV. After full conditioning and beamline integration in Europe, the cavities were installed in the accelerator with special care given to the alignment with respect to the rest of the components. The RF line, cooling circuits, and instrumentation were also mounted. The cavities were operated with an FPGA-based LLRF system. A re-conditioning of the cavities was performed in the first place, followed by tests with a pulsed beam with increasing currents. A maximum pulsed beam current of 100 mA was reached while operating the buncher cavities, under which they reached voltages up to 340 kV and 260 kV respectively. As expected, the beam loading was significant, leading to a series of difficulties and required strategies for a good operation that are discussed in this paper. The effect on the beam dynamics, measured by beam position monitors downstream of the bunchers is also discussed. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB272  
About • paper received ※ 19 May 2021       paper accepted ※ 02 September 2021       issue date ※ 18 August 2021  
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THPAB296 The Spallation Neutron Source Normal Conducting Linac RF System Design for the Proton Power Upgrade Project 4383
 
  • J.S. Moss, M.T. Crofford, S.W. Lee, G.D. Toby
    ORNL, Oak Ridge, Tennessee, USA
  • M.E. Middendorf
    ORNL RAD, Oak Ridge, Tennessee, USA
  
  Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC05-00OR22725.
The Proton Power Upgrade (PPU) project at the Spallation Neutron Source will double the available proton beam power from 1.4 to 2.8 MW by increasing the beam energy from 1.0 to 1.3 GeV and the beam current from 26 to 38 mA. The increase in beam current resulted in the need to redesign the existing normal conducting linac (NCL) RF Systems. High-power testing of the existing NCL RF Systems configured to accelerate PPU-level beam provided the data used to make the final design decisions. This paper describes the development and execution of those in-situ tests and the subsequent results. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB296  
About • paper received ※ 17 May 2021       paper accepted ※ 22 July 2021       issue date ※ 20 August 2021  
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FRXB02 Development of 36 GHz RF Systems for RF Linearisers 4518
 
  • A. Castilla, G. Burt
    Lancaster University, Lancaster, United Kingdom
  • M. Behtouei, B. Spataro
    INFN/LNF, Frascati, Italy
  • G. Burt
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • J.C. Cai, A. Castilla, A. Latina, X. Liu, I. Syratchev, X.W. Wu, W. Wuensch
    CERN, Geneva, Switzerland
  • J.C. Cai, A. Castilla
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • A.W. Cross, L. Zhang
    USTRAT/SUPA, Glasgow, United Kingdom
  • L.J.R. Nix
    University of Strathclyde, Glasgow, United Kingdom
  
  Funding: This project has received funding from the European Union’s Horizon2020 research and innovation programme under grant agreement No 777431.
As part of the deign studies, the CompactLight project plans to use an injector in the C-band. Which constitutes a particular complication for the harmonic system in charge of linearising the beam’s phase space, since it means its operation frequency could be higher than the standard X-band RF technologies. In the present work, we investigated a 36 GHz (Ka-band) as the ideal frequency for the harmonic system. A set of structure designs are presented as candidates for the lineariser, based on different powering schemes and pulse compressor technologies. The comparison is made both in terms of beam dynamics and RF performance. Given the phase stability requirements for the MW class RF sources needed for this system, we performed careful studies of a Gyro-Klystron and a multi-beam klystron as potential RF sources, with both showing up to 3 MW available power using moderate modulator voltages. Alternatives for pulse compression at Ka-band are also discussed in this work. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-FRXB02  
About • paper received ※ 17 May 2021       paper accepted ※ 19 July 2021       issue date ※ 25 August 2021  
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FRXB03
 MgB2 Based High-Current Power Transmission Lines for the HL-LHC Magnets: From Concept to Prototype Validation  
 
  • A. Ballarino
    CERN, Geneva, Switzerland
  
  The powering of the HL-LHC magnets requires transferring multiple large quasi-DC currents from the power converters, located in new radiation-free underground galleries, to the magnets. Superconducting power transmission lines based on MgB2 superconductor, called Superconducting Links, ensure the electrical transmission from the current leads, near the power converters, to the magnets in the LHC main tunnel. They span a physical distance of up to about 120 metres, snaking through a complex underground environment that includes a vertical path of about 10 metres, and transfer DC currents totalling up to 120 kA at temperatures of up to 25 K. This paper summarizes the development done in order to conceive, construct and industrialize cold powering systems including 100 kA Superconducting Links. The systems, which are cooled by the forced flow of helium gas, incorporate HTS REBCO based current leads and Nb-Ti terminations for the connection to the magnets’ busbars. Demonstrator cold powering systems were recently constructed and tested at CERN in nominal and transient conditions representative of the final operation modes. The results from these tests are also presented and discussed.  
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FRXB06
 Direct response time measurements on semiconductor photocathodes  
 
  • G. Loisch, M. Groß, D.K. Kalantaryan, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, F. Stephan, G. Vashchenko, T. Weilbach
    DESY Zeuthen, Zeuthen, Germany
  • Y. Chen, S. Lederer
    DESY, Hamburg, Germany
  • L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  • R. Valizadeh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  Semiconductor photocathodes like Cs2Te enable stable electron sources with high photon to electron conversion rate (quantum efficiency, QE) for high brightness photoinjectors. Besides QE, work function and vacuum stability, bunch lengthening is a key figure of merit for these sources, resulting from UV photon penetration into the semiconductor and scattering of excited electrons before emission. These processes and their statistical variation lead to a delay, as well as to lengthening of the extracted electron bunch w.r.t. the incident laser pulse, often referred to as "response time". Thus far, no direct measurement of the response time of Cs2Te, one of the most widely used cathode materials, has been reported. As such a measurement is crucial for photocathode laser based bunch shaping, short bunch applications, emission modeling and for evaluating new cathode materials like CsKSb, a measurement procedure has been established at the photoinjector test facility at DESY in Zeuthen (PITZ) to measure longitudinal bunch shape variation due to cathode emission effects. Here, we introduce the method and show first results on direct cathode response measurements of Cs2Te cathodes.  
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