Keyword: beam-loading
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MOPMF076 Energy Spread Compensation in Arbitrary Format Multi-Bunch Acceleration With Standing Wave and Traveling Wave Accelerators acceleration, positron, cavity, linac 307
 
  • M. Kuriki
    HU/AdSM, Higashi-Hiroshima, Japan
 
  In the E-driven ILC (International Linear Collider) positron source, the beam is generated and accelerated in a multi-bunch format with mini-trains. The macro-pulse contains 2 to 8 mini-trains with several train gaps, because the pulse format is a copy of a part of the bunch storage pattern in DR (Damping Ring). This pulse format causes a variation of the accelerator field in the pulse due to the transient beam loading and an intensity fluctuation of captured positron. In this article, we discuss the compensation of the energy spread of such beam in standing wave and traveling wave accelerators. For standing wave accelerator, it can be compensated by switching input RF at appropriate timings. For traveling wave accelerator, it can be compensated by amplitude modulation of the input RF.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF076  
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MOPMF077 A Design Study of the Electron-driven ILC Positron Source Including Beam Loading Effect positron, cavity, acceleration, booster 311
 
  • H. Nagoshi, M. Kuriki
    HU/AdSM, Higashi-Hiroshima, Japan
  • S. Kashiwagi
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  • K. Negishi
    Iwate University, Morioka, Iwate, Japan
  • T. Omori, M. Satoh, Y. Seimiya, J. Urakawa
    KEK, Ibaraki, Japan
  • Y. Sumitomo
    LEBRA, Funabashi, Japan
  • T. Takahashi
    Hiroshima University, Graduate School of Science, Higashi-Hiroshima, Japan
 
  The International Linear Collider (ILC) is a next-generation accelerator for high-energy physics to study the Higgs and top sector in the Standard Model, and new physics such as supersymmetry and dark matter. ILC positron source based on Electron-driven method has been proposed as a reliable technical backup. In this article, we report the design study of the positron source based on the off-the-shelf RF components. The positron is generated and accelerated in a multi-bunch format. To compensate the energy variation by the transient beam loading effect, we employ AM (Amplitude Modulation) technique and the results were 16.60 ± 0.14 MV (peak-to-peak) for L-band 2m cavity driven by 22.5 MW power and 25.76 ± 0.19 MV (peak-to-peak) for S-band 2m ac-celerator driven by 36 MW power with 0.78 A beam load-ing.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF077  
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MOPMK017 Transient Beam Loading Due to the Bunch Train Gap and Its Compensation Experiments at BEPC-II and ALS cavity, experiment, feedback, luminosity 390
 
  • H. Wang, R.A. Rimmer, S. Wang
    JLab, Newport News, Virginia, USA
  • J.P. Dai, Q. Qin, J. Xing, J.H. Yue, Y. Zhang
    IHEP, Beijing, People's Republic of China
  • D. Teytelman
    Dimtel, San Jose, USA
 
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Non-uniform bunch fill patterns in storage rings, driven by the need to provide gaps for beam aborting and ion clearing cause a large beam loading change in the RF cavities. The induced turn-periodic transient in the cavity voltage modulates longitudinal beam properties along the train, such as synchronous position and bunch length. In the EIC design, due to the asymmetric bunch train structure between the electron and the ion beam, such modulation results in shifting collision point and leads to reduced luminosity. We have carried out the beam based experiments at BEPC-II and ALS using bunch-by-bunch diagnostic capabilities of the coupled-bunch feedback systems to study this transient effect. A modulated bunch filling pattern with higher charge density around the gap has been demonstrated to be effective in partially compensating this transient modulation. Details of the experimental setups and the data analysis will be presented to this conference.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMK017  
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MOPML055 Preliminary Physics Design of a Linac with the Variable Energy for Industrial Applications linac, electron, gun, simulation 530
 
  • Zh. X. Tang
    USTC, Hefei, Anhui, People's Republic of China
  • L. Wang, D.R. Xu
    USTC/NSRL, Hefei, Anhui, People's Republic of China
 
  This paper describes the physics design of a S-band (2856 MHz) linear accelerator (linac) with variable energy tuning. The system consists of a DC gun for generating electron, prebuncher for velocity modulation and two travelling wave (TW) accelerating sections for acceleration. The accelerating structure is a 2'Ð/3 mode constant gradient TW structure, which comprises TW buncher cells, followed by uniform cells. The structure is designed to accelerate 45 keV electron beam from the electron gun to 3.2 MeV, and then 10 MeV. An important feature of the TW linac is that the RF output power of the first linac is as the RF input power of the second linac. Three dimensional transient simulations of the accelerating structure along with the input and output couplers have been performed to explicitly demonstrate this feature. Beam dynamics is performed to calculate the beam parameter.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPML055  
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TUPMF081 Microphonic Detuning Induced Coupler Kick Variation at LCLS-II cavity, linac, laser, free-electron-laser 1456
 
  • T. Hellert
    DESY, Hamburg, Germany
  • W. Ackermann, H. De Gersem
    TEMF, TU Darmstadt, Darmstadt, Germany
  • C. Adolphsen, Z. Li, C.E. Mayes
    SLAC, Menlo Park, California, USA
 
  The LCLS-II free-electron laser will be an upgrade of the existing Linac Coherent Light Source (LCLS), including a 4 GeV CW superconducting linac based on the TESLA technology. The high quality factor of the cavity makes it very sensitive to vibrations. The shift of its eigenfrequency (i.e., detuning) will be compensated by the power source in order to assure a constant accelerating voltage. Significant variations of the forward power are expected which result in coupler kick variations induced by the fundamental power coupler. In this work we estimate the magnitude of trajectory jitter caused by these variations. High precision 3D field maps including standing and traveling-wave components for a cavity with the LCLS-II coupler design are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF081  
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TUPML005 Study of a Dielectric Disk Structure for Short Pulse Two-Beam Acceleration acceleration, impedance, collider, linear-collider 1539
 
  • J.H. Shao, M.E. Conde, D.S. Doran, J.F. Power
    ANL, Argonne, Illinois, USA
  • C.-J. Jing
    Euclid TechLabs, LLC, Solon, Ohio, USA
 
  Argonne Flexible Linear Collider (AFLC), a proposed 3 TeV electron-positron linear collider based on two-beam acceleration (TBA) scheme, applies a short pulse length (∼20 ns) to obtain a high accelerating gradient (267 MV/m) and a compact footprint (∼18 km). The baseline design of the main accelerator section adopts 26 GHz K-band traveling-wave dielectric-loaded accelerators (DLA) with an rf to beam efficiency 𝜂𝑟𝑓 −𝑏𝑒𝑎𝑚 of 27%. Recently, an alternative structure which is similar to a metallic disk-loaded one but with dielectric disks, noted as dielectric disk accelerator (DDA), has been investigated and optimized, leading to ∼45% improvement in 𝜂𝑟𝑓 −𝑏𝑒𝑎𝑚. To demonstrate the key technologies, an X-band prototype structure has been designed and will be tested at Argonne Wakefield Accelerator (AWA) facility with a 300 MW metallic power extractor. Detailed comparison between K-band DLA and DDA for AFLC main accelerator as well as the preliminary design of the X-band DDA prototype will be presented in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML005  
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TUPML059 Slice Energy Spread Optimization for a 5 GeV Laser-Plasma Accelerator plasma, laser, simulation, electron 1670
 
  • X. Li, P.A.P. Nghiem
    IRFU, CEA, University Paris-Saclay, Gif-sur-Yvette, France
  • A. Mosnier
    CEA/IRFU, Gif-sur-Yvette, France
 
  GeV-scale laser-plasma accelerating modules can be integrated into a multi-staged plasma linac for driving compact X-ray light sources or future colliders. Such a plasma module, operating in the quasi-linear regime, has been designed for the 5 GeV laser plasma acceleration stage (LPAS) of the EuPRAXIA project. Although it can be employed to optimize the total energy spread, the beam loading effect introduces an non-negligible slice energy spread to the beam. In this paper, we study the slice energy spread from linear theory, establishing a relationship between it and the laser-plasma parameters. To reduce the slice energy spread, simulations have been carried out for various plasma densities and laser strengths. The results will be discussed and compared with the theory.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML059  
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WEPAL016 Tensile Fracture Test of Metallic Wire of Beam Profile Monitors linac, electron, cavity, controls 2183
 
  • A. Miura, Y. Kawane, K. Moriya
    JAEA/J-PARC, Tokai-mura, Japan
  • S. Fukuoka
    Nihon Koshuha Co. Ltd, Yokohama, Japan
  • K. Futatsukawa, T. Miyao
    KEK, Ibaraki, Japan
 
  In order to mitigate the beam loss during a beam transportation in a high-brilliant accelerator facilities, wire-based profile monitors are used to measure by both transverse and longitudinal beam profiles using wire-scanner monitors (WSMs) and bunch-shape monitors (BSMs) for the tuning of quadrupole magnets and bunching cavities. Signals are come from the direct interaction between a metallic wire and beam. We have used the tungsten wire as a high melting-point material by estimation of heat loading during the impact of beam particles. In addition, a spring is applied for the relaxing a sag under wire's own weight. A tensile fracture test is conducted by supplying an electrical current as a simulated beam-heat loading. As the results, we obtained the relation between the thermal limit to break down and tension loading of tungsten wire.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL016  
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WEPAL023 Pulsed Operation at MAMI with High Beam Loading experiment, beam-losses, operation, klystron 2206
 
  • M. Dehn, K. Aulenbacher, F. Fichtner, P. Jennewein, W. Klag, H.-J. Kreidel, J.R. Röthgen
    IKP, Mainz, Germany
 
  Funding: Work supported by DFG (CRC 1044) and the German federal state of Rhineland-Palatinate
The Mainz Microtron Accelerator (MAMI) is a microtron cascade which is normally operated CW for particle physics experiments. For certain investigations it is necessary to use a pulsed beam (macro pulses, several milliseconds). Up to now this pulsed mode can only be applied if the beam loading for the accelerating RF structures is negligible. To achieve higher pulse intensities the accelerator RF infrastructure needs to be equipped with feed-forward techniques to compensate for the expected beam loading. To monitor beam losses the machine protection system at MAMI needs to be extended to be able to localize fast occurrences of beam losses. This paper will present the possibilities being investigated to allow pulsed operation of MAMI within the near future.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL023  
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WEPMF058 Anomaly Detection for Cavity Signals - Results from the European XFEL cavity, flattop, FEL, simulation 2502
 
  • A.S. Nawaz, S. Pfeiffer
    DESY, Hamburg, Germany
  • G. Lichtenberg
    HAW, Hamburg, Germany
  • P. Rostalski
    Institute for Electrical Engineering in Medicine, Lübeck, Germany
 
  The data throughput of the European XFEL DAQ is about 1.5 Gb/s. Data depicting the cavity signal behavior is currently only saved manually. This either happens, when cavity tests are being performed, or an operator detects a fault in the cavity system, that has to be further investigated. Those instances of interest are neither systematically nor automatically stored. It can therefore be assumed that unwanted or degraded cavity behavior is detected late or not at all. It is proposed to change the focus from detecting known faults (such as quenches) to additionally detect anomalies in the cavity system behavior. In order to detect anomalies in the cavity signals, an algorithm is proposed using a cavity model. It aims on finding those data sets, which diverge from the nominal cavity behavior, saving those instances for later analysis. The nominal behavior is defined by the cavity electromagnetic resonance model with beam loading as well as the model for the mechanical oscillations due to the Lorentz Forces. By using such an approach, the detection of anomalies, as well as faults could be automated. This contribution aims to summarize the influence of beam loading on the detection and gives examples for anomalies that were found in several cavities.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF058  
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THPAK037 Beam-Loading Transients and Bunch Shape in the Operation of Passive Harmonic Cavities in the ALS-U cavity, simulation, impedance, controls 3298
 
  • Z. Pan, S. De Santis, C. Steier, C. Sun, M. Venturini
    LBNL, Berkeley, USA
  • T. Hellert
    DESY, Hamburg, Germany
  • C.-X. Tang
    TUB, Beijing, People's Republic of China
 
  The ALS-U is a major upgrade of the LBNL ALS to a diffraction limited light source. The current plan is to replace all the vacuum and magnet components while retaining the existing 500 MHz main and third-harmonic, passively operated, rf cavities, but replacement of the existing rf cavities is also being considered. A new feature, is represented by beam-loading transients associated with a beam consisting of 11 bunch trains separated by 10 ns gaps as needed to enable on-axis swap-out injection. In this paper we study these transients and the associated bunch-to-bunch phase, length, and profile variations.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK037  
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THPML083 Iterative Learning Control to Cancel Beam Loading Effect on Amplitude and Phase of the Accelerating Field controls, cavity, feedback, simulation 4847
 
  • Z. Shahriari, K. Fong
    TRIUMF, Vancouver, Canada
  • G. A. Dumont
    UBC, Vancouver, Canada
 
  Funding: This research is supported by TRIUMF through federal funding via a contribution agreement with the National Research Council of Canada.
Iterative learning control (ILC) is an open loop control strategy that improves the performance of a repetitive system through learning from previous iterations. ILC can be used to compensate for a repetitive disturbance like the beam loading effect in resonators. Assuming that the beam loading disturbance is identical for all iterations, the learning law can be non-causal; it can anticipate the disturbance and preemptively counteract its effect. In this work, we aim to use ILC to cancel beam loading effect on amplitude and phase. Feedback controllers are not fast enough for this purpose. A normal feed forward controller may not be sufficient as well if there is a difference between the feed forward signal and the beam loading current. Therefore, the goal is to use ILC to adaptively cancel the beam loading effect.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML083  
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THPML125 Efficiency Analysis of High Average Power Linacs for Environmental and Industrial Applications linac, impedance, higher-order-mode, coupling 4970
 
  • M. Shumail, V.A. Dolgashev
    SLAC, Menlo Park, California, USA
 
  Funding: U.S. Department of Energy, HEP under Research Opportunities in Accelerator Stewardship: LAB 16-1438.
We present comprehensive efficiency equations and useful scaling laws to optimally determine design parameters for high efficiency rf linacs. For the first time we have incorporated the parasitic losses due to the higher order cavity modes into the efficiency analysis of the standing wave (SW) and travelling wave (TW) accelerators. We have also derived the efficiency equations for a new kind of attenuation-independent-impedance travelling wave (ATW) accelerators where the shunt impedance can be optimized independent of the group velocity. We have obtained scaling laws which relate the rf to beam efficiency to the linac length, beam aperture radius , phase advance per cell, and the type of accelerating structure: SW versus TW, disk-loaded (DL) versus nose-cone (NC). We give an example of using these scaling laws to determine a feasible set of parameters for a 10 MeV, 10 MW linac with 97.2% efficiency.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML125  
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FRXGBD3 Application of Carbon Nanotube Wire for Beam Profile Measurement of Negative Hydrogen Ion Beam electron, rfq, operation, linac 5022
 
  • A. Miura, K. Moriya
    JAEA/J-PARC, Tokai-mura, Japan
  • T. Miyao
    KEK, Ibaraki, Japan
 
  A wire scanner monitor using metallic wire is reliably employed for the beam profile measurement in the J-PARC linac. Because the loading of negative hydrogen (H) ion beam on a wire increases under high-current beam operation, we focus on using a high-durability beam profile monitors by attaching another wire material. Carbon nanotubes (CNT) are made of graphite in a cylindrical shape and have a tensile strength not less than 100 times that of steel. The electric conductivity has higher than that of metals, and hardness is endured thermally around 3000°C in a vacuum circumstance. We applied the CNT wires to WSM and measured transverse profiles with a 3-MeV and 191-MeV H beam. As a result, we obtained the equivalent signal levels taken by carbon wire made of polyacrylonitrile without any damage. In this paper, the signal response when the CNT is irradiated with an H beam and the result of beam profile measurement. In addition, the surface of CNT after 3-MeV beam operation was observed.  
slides icon Slides FRXGBD3 [2.562 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-FRXGBD3  
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