Keyword: impedance
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MOPMF020 Higher Order Mode Coupling Options for the eRHIC Crab Cavity cavity, HOM, damping, coupling 121
 
  • Q. Wu, I. Ben-Zvi, S. Verdú-Andrés, B. P. Xiao
    BNL, Upton, Long Island, New York, USA
  • I. Ben-Zvi
    Stony Brook University, Stony Brook, USA
 
  Funding: This work was supported by the US Department of Energy via Brookhaven Science Associates LLC under contract no. DE-SC0012704.
The eRHIC crab cavity adopts the double quarter wave structure developed at Brookhaven National Lab for the LHC Hi-Lumi upgrade crab cavities. The cavity's fundamental mode is at 338 MHz with the first higher order mode more than 180 MHz above that. We looked into the higher order mode distribution up to 2 GHz, and considered various locations and geometries of the coupling scheme. The cylindrical outer shell of the cavity allowed various possibilities for coupler port openings on all the walls, which were difficult for the narrow waist of the LHC double quarter wave crab cavities. Beam pipe absorbers are also options for simpler high frequency modes damping. Some preliminary high pass filter design will also be discussed in this paper.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF020  
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MOPMF029 FCC-hh transverse impedance budget injection, feedback, laser, electron 149
 
  • S. Arsenyev, D. Schulte
    CERN, Geneva, Switzerland
  • O. Boine-Frankenheim
    GSI, Darmstadt, Germany
 
  Contributions of different machine elements of the proposed Future Circular Collider (FCC-hh) impedance budget are calculated based on beam stability considerations. For each element (the beamscreen, the collimators, etc), effective impedances are calculated at the injection energy and at the collision energy for considered instabilities. The considered instabilities include the transverse coupled bunch instability (TCBI) and the transverse mode coupling instability (TMCI). Limitations to each total effective impedance are estimated and the critical points in the impedance budget are determined.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF029  
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MOPMF030 Broadband Impedance of Pumping Holes and Interconnects in the FCC-hh Beamscreen wakefield, coupling, electronics, injection 153
 
  • S. Arsenyev, D. Schulte
    CERN, Geneva, Switzerland
 
  In the proposed Future Circular Collider (FCC-hh) pumping holes and interconnects between sections of the beamscreen can be sources of unwanted broadband impedance, potentially leading to the transverse mode coupling instability (TMCI). The pumping holes pose a greater challenge to the impedance calculation due to their small contribution per hole. Unlike for the Large Hadron Collider (LHC), analytical methods cannot be applied due to the complex beamscreen geometry and the greater size of the holes. Instead, two computational methods are used and compared to each other. For the interconnects, the impedance due to a sophisticated system of tapers is also estimated using computational methods.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF030  
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MOPMF031 Modelling Wake Impedance of a Rough Surface in Application to the FCC-hh Beamscreen coupling, electron, laser, vacuum 157
 
  • S. Arsenyev, D. Schulte
    CERN, Geneva, Switzerland
 
  The inner surface of the future circular collider (FCC-hh) beamscreen is proposed to be laser-treated in order to mitigate the electron cloud build-up. However, the rough structure of the treated surface can result in unwanted impedance increase, potentially leading to the transverse mode coupling instability (TMCI). Three models have been adopted to estimate the wake impedance of a beamscreen with a rough surface. The models use the resistive wall formalism generalized for the case of an arbitrary surface impedance. The results apply to a beamscreen of a circular cross-section with the homogeneously rough inner surface for the case of ultrarelativistic particles. The free parameters of the models were fit into preliminary measurements of the surface resistivity, giving, as a result, a range of the real and the imaginary parts of the wake impedance.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF031  
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MOPMF036 FCC-ee Hybrid RF Scheme cavity, HOM, operation, radiation 173
 
  • Sh. Gorgi Zadeh, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • R. Calaga, F. Gerigk
    CERN, Geneva, Switzerland
 
  Funding: Research supported by the FCC design study
For FCC-ee, the range of beam energies and beam currents is large between each mode of operation, all scaled to an available 50 MW maximum power per beam. The two limiting scenarios for the RF system design are at low energy (45 GeV) with high beam current (1.45 A) and the highest energy (182.5 GeV) with a radiation loss reaching 8.92 GeV per turn. In this paper, RF staging with a hybrid scheme using both 400 MHz and 800 MHz is proposed to mitigate the requirements on the two extremes. Relevant comparisons are made with respect to using only a single frequency for all modes.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF036  
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MOPMF064 High-Energy LHC Design optics, luminosity, injection, proton 269
 
  • F. Zimmermann, D. Amorim, S. A. Antipov, S. Arsenyev, M. Benedikt, R. Bruce, M.P. Crouch, S.D. Fartoukh, M. Giovannozzi, B. Goddard, M. Hofer, R. Kersevan, V. Mertens, Y. Muttoni, J.A. Osborne, V. Parma, V. Raginel, S. Redaelli, T. Risselada, I. Ruehl, B. Salvant, D. Schoerling, E.N. Shaposhnikova, L.J. Tavian, E. Todesco, R. Tomás, D. Tommasini, F. Valchkova-Georgieva, V. Venturi, D. Wollmann
    CERN, Geneva, Switzerland
  • J.L. Abelleira, E. Cruz Alaniz, P. Martinez Mirave, A. Seryi, L. van Riesen-Haupt
    JAI, Oxford, United Kingdom
  • A. Apyan
    ANSL, Yerevan, Armenia
  • J. Barranco García, L. Mether, T. Pieloni, L. Rivkin, C. Tambasco
    EPFL, Lausanne, Switzerland
  • F. Burkart
    DESY, Hamburg, Germany
  • Y. Cai, Y.M. Nosochkov
    SLAC, Menlo Park, California, USA
  • G. Guillermo Cantón
    CINVESTAV, Mérida, Mexico
  • K. Ohmi, K. Oide, D. Zhou
    KEK, Ibaraki, Japan
 
  In the frame of the FCC study we are designing a 27 TeV hadron collider in the LHC tunnel, called the High Energy LHC (HE-LHC).  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF064  
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MOPMK014 Resistive-Wall Impedance of Insertions for FCC-hh insertion, optics, experiment, lattice 378
 
  • B. Riemann, S. Khan
    DELTA, Dortmund, Germany
  • S. Arsenyev, D. Schulte
    CERN, Geneva, Switzerland
 
  Funding: This work is supported by the German Ministry of Education & Research (BMBF, funding code 05P15PERB1) and CERN (reference numbers KE3123, EDMS 1606722).
In this work, transverse and longitudinal resistive-wall impedances for beam pipes in the experiment, injection, extraction and RF systems insertion regions of the Future Hadron-Hadron Collider (FCC-hh) are computed based on contributions from different given cross sections of the surrounding (elliptical) chamber parts along the beam path, their temperature-dependent conductivities, and optical functions. An emphasis is placed on the behaviour of transverse impedance in the main experimental regions (A and G), where maximum beta values of 104 to 105 m occur in dependence of the operation mode respectively lattice configuration. Main contributions to the transverse and longitudinal impedance budget are identified, and possibilities of reducing them are discussed.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMK014  
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MOPML052 The Path to Compact, Efficient Solid-State Transistor-Driven Accelerators cavity, electron, linac, simulation 520
 
  • D.C. Nguyen, C.E. Buechler, G.E. Dale, R.L. Fleming, M.A. Holloway, J.W. Lewellen, D. Patrick
    LANL, Los Alamos, New Mexico, USA
  • V.A. Dolgashev, E.N. Jongewaard, E.A. Nanni, J. Neilson, A.V. Sy, S.G. Tantawi
    SLAC, Menlo Park, California, USA
 
  Funding: Research presented in this work is supported by (LANL) Laboratory Directed Research and Development 20170521ER and by (SLAC) Department of Energy contract DE-AC02-76SF00515.
Small, lightweight, few-MeV electron accelerators that can operate with low-voltage power sources, e.g., solid-state transistors running on 50 VDC, instead of high-voltage klystrons, will provide a new tool to enhance existing applications of accelerators as well as to initiate new ones. Recent advances in gallium nitride (GaN) semiconductor technologies * have resulted in a new class of high-power RF solid-state devices called high-electron mobility transistors (HEMTs). These HEMTs are capable of generating a few hundred watts at S-, C- and X-bands at 10% duty factor. We have characterized a number of GaN HEMTs and verified they have suitable RF characteristics to power accelerator cavities **. We have measured energy gain as a function of RF power in a single low-beta C-band cavity. The HEMT powered RF accelerators will be compact and efficient, and they can operate off the low-voltage DC power buses or batteries. These all-solid-state accelerators are also more robust, less likely to fail, and are easier to maintain and operate. In this poster, we present the design of a low-beta, 5.1-GHz cavity and beam dynamics simulations showing continuous energy gain in a ten-cavity C-band prototype.
* See for example, http://www.wolfspeed.com/downloads/dl/file/id/463/product/174/cghv59350.pdf
** J.W. Lewellen et al., Proceedings of LINAC2016, Paper MO3A03
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPML052  
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TUXGBF3 Reduction of the Kicker Impedance Maintaining the Performance of Present Kicker Magnet at RCS in J-PARC kicker, simulation, synchrotron, extraction 616
 
  • Y. Shobuda, Y. Irie, T. Takayanagi, T. Togashi, K. Yamamoto, M. Yamamoto
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
 
  The present kicker at RCS in J-PARC is designed to make a waveform by superposing the forward and backward currents from the power source to extract beams, so that one terminal of the kicker is shorted and the other one is open. On the other hand, the kicker impedance is the dominant source of the beam instability at the RCS. This report proposes a scheme to reduce the kicker impedance, maintaining the beneficial of the superposition of currents with the present kicker magnet.  
slides icon Slides TUXGBF3 [9.951 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUXGBF3  
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TUXGBF4 ORBIT Simulation, Measurement and Mitigation of Transverse Beam Instability in the Presence of Strong Space Charge in the 3-GeV RCS of J-PARC simulation, injection, acceleration, space-charge 620
 
  • P.K. Saha, H. Harada, N. Hayashi, H. Hotchi, Y. Shobuda, F. Tamura
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
 
  The transverse impedance of eight extraction pulse kicker magnets (KM) is extremely strong source of transverse beam instability in the 3-GeV RCS (Rapid Cycling Synchrotron) at J-PARC. To realize the designed 1 MW beam power, collective beam dynamics with including the space charge effect for the coupled bunch instabilities excited by the KM impedance and associated measures were studied by incorporating all realistic time-dependent machine parameters in the ORBIT 3-D particle tracking code. The simulation results were all reproduced by measurements and, as a consequence, an acceleration of 1 MW beam power has been successfully demonstrated. In order to maintain variation of the RCS parameters required for multi-user operation, realistic measures for beam instability mitigation were proposed and also been successfully implemented in reality. To further increase the RCS beam power, beam stability issues and possible measures beyond 1 MW beam power are also considered.  
slides icon Slides TUXGBF4 [2.246 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUXGBF4  
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TUPAF024 Impedance and Instability Studies in LEIR with Xenon space-charge, coupling, accumulation, injection 720
 
  • N. Biancacci, H. Bartosik, M. Gąsior, S. Hirlaender, V. Kain, T.E. Levens, E. Métral
    CERN, Geneva, Switzerland
  • M. Migliorati
    Rome University La Sapienza, Roma, Italy
 
  In 2017, the LEIR accelerator has been operated with Xe39+ beam for fixed target experiments in the SPS North Area. The different ion species, with respect to the usually operated Pb54+, allowed for additional comparative measurements of tune shift versus intensity at injection energy both in coasting and bunched beams. The fast transverse instability observed for high accumulated intensities has been as well characterized and additional observations relevant to impedance have been collected from longitudinal Schottky signal and BTF measurements. The results of these measurements are summarised and compared to the currently developed machine impedance model.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF024  
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TUPAF087 A Two-Stage Splitring-RFQ for High Current Ion Beams at Low Frequencies rfq, simulation, acceleration, resonance 941
 
  • M. Baschke, H. Podlech, A. Schempp
    IAP, Frankfurt am Main, Germany
 
  Funding: HIC for FAIR, BMBF Contr. No. 05P15RFRBA
For several accelerator projects RFQs are the first stage of acceleration. To reach high intensities a new Splitring-RFQ is investigated. Not only a high current and high beam quality/brilliance should be achieved, also a good tuning flexibility and comfort for maintenance are part of the study. The RFQ will consist of two stages with 27 MHz and 54 MHz to accelerate ions with an A/q of 60 up to energies of 200 keV/u. RF simulations with CST MWS have been performed to obtain the quality factor, shunt impedance and voltage distribution as well as tuning possibilities. The results and the status of the project will be presented.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF087  
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TUPAL022 Low-Reflection RF Window for ACS Cavity in J-PARC Linac cavity, Windows, linac, proton 1051
 
  • J. Tamura, Y. Kondo, T. Morishita
    JAEA/J-PARC, Tokai-mura, Japan
  • H. Ao
    FRIB, East Lansing, USA
  • F. Naito, M. Otani
    KEK, Tokai, Ibaraki, Japan
  • Y. Nemoto
    Nippon Advanced Technology Co., Ltd., Tokai, Japan
 
  In the Japan Proton Accelerator Research Complex (J-PARC) linac, the Annular-ring Coupled Structure (ACS) cavities have been stably operating. To maintain this operation availability, we manufactured three backups of the pillbox-type RF windows for the ACS cavities in fiscal year 2015 and 2017. It is desirable to minimize the RF reflection of the RF window to prevent standing waves from exciting between the cavity and the RF window, and not to significantly change the optimized coupling factor between the cavity and the waveguide. To realize the minimization, the relative permittivities of the ceramic disks of the RF windows were evaluated by measuring the resonant frequencies of the pillbox cavity containing the ceramic disk. On the basis of the evaluated relative permittivities, the pillbox-part lengths of the RF windows were determined. The measured Voltage Standing Wave Ratios (VSWRs) of the manufactured RF windows are just about 1.08 and these are applicable for the practical use.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAL022  
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TUPMF021 Investigation of Options for Damping Trapped IVU Resonances resonance, damping, undulator, simulation 1296
 
  • R.T. Dowd
    AS - ANSTO, Clayton, Australia
  • W.J. Chi, D. Pelz
    RFS, Kilsyth, Australia
 
  Trapped resonances have been observed within the three In-Vacuum Undulators (IVUs) insertion devices at the Australian Synchrotron. These resonances can create vertical beam instability if not controlled through transverse feedback systems. Similar resonances have been observed at other synchrotron light sources around the world. Under certain conditions of undulator gap, these resonances can couple quite strongly to the beam, requiring high feedback gain. An investigation of the resonances has been carried out using 3D eigenmode and wakefield simulations to understand the resonances and determine the effectiveness of various schemes for modifying the damping the resonances.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF021  
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TUPMF027 Impedance Modeling for eRHIC vacuum, dipole, quadrupole, electron 1309
 
  • A. Blednykh, G. Bassi, M. Blaskiewicz, C. Hetzel, V. Ptitsyn, V.V. Smaluk, F.J. Willeke
    BNL, Upton, Long Island, New York, USA
 
  Funding: Work supported by the US DOE under contract number DE-SC0012704
The impedance budget for the eRHIC project is discussed at its earlier stage of development. As a first step, with the eRHIC lattice and beam parameters , we use the geometric impedances of the vacuum chamber components simulated for the NSLS-II project. The impedance budged will be updated next with more impedance data simulated for the optimized eRHIC vacuum components. It will allows us to keep track on the collective effects changes with more realistic components added to the ring.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF027  
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TUPMF053 Longitudinal Impedance Measurement of the Strip-Line Kicker for High Energy Photon Source (HEPS) kicker, simulation, coupling, distributed 1379
 
  • S.K. Tian, J. Chen, Y. Jiao, H. Shi, L. Wang, N. Wang
    IHEP, Beijing, People's Republic of China
 
  The High Energy Photon Source (HEPS) is a 6-GeV, kilometer-scale storage ring light source to be built in China. One of the main design challenges of the storage ring is to minimize collective instabilities associated with the impedance of small-aperture vacuum components. In this paper we present beam coupling impedance measurements obtained by the well known coaxial wire method, for the HEPS Strip-Line kicker. The frequency dependent real and imaginary parts of the distributed impedance are obtained from the measured S-parameters.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF053  
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TUPMF071 Status of Impedance Modeling for the PETRA IV wakefield, lattice, synchrotron, status 1423
 
  • Y.-C. Chae, R. Wanzenberg
    DESY, Hamburg, Germany
 
  The diffraction limited synchrotron light source envisioned for the PETRA IV project will require strong focusing to produce the small emittances in both planes. The large natural chromaticity together with small dispersion will require very strong sextupoles. In order to cope with high gradient magnets the radius of vacuum chamber tends to be in the range of 10 mm, which is very small compared to the current 40-mm wide elliptic chamber. The impedance element in the PETRA III was scaled down to fit into the smaller aperture so that the short range wakepotential can be computed numerically. For instance the beam position monitor (BPM) was reduced to 60% in dimension so that it can be used in PETRA IV. Even if the actual design of hardware does not exist yet, we assume that generic feature of PETRA III model is still valid. In this paper we report the up-to-date information on impedance model of PETRA IV together with the preliminary impedance budget based on the analytical formula. We also report the specific studies carried out to understand the kickfactor scaling with the chamber aperture whose radius is in the range of 8-12 mm.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF071  
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TUPMF073 Impedance Optimization of Small Gap Chambers for the High Single Bunch Current Operation at the Undulator Based Light Sources lattice, undulator, ECR, simulation 1430
 
  • Y.-C. Chae
    DESY, Hamburg, Germany
 
  In the undulator based light sources the intensity limit of single bunch is often determined by the strong vertical instability caused by the wakefield in the ring, where the undulator itself is large impedance source. The optimization of transition from the large aperture to undulator's small-gap chamber is on-going research topic in an effort to reduce the vertical impedance; at the same time, the demand on single-bunch current is high from the timing-mode x-ray user community. In this paper, after showing the results obtained by exploring the parameter space guided by Stupakov's formula, we propose the linearly-segmented transition which can reduce the impedance down to 60% or less of the original linear taper. The reduction can be utilized either to increase the bunch current substantially or to install a smaller gap chamber without impacting the bunch current limit. For the definite result we considered the transition between two ellipses, namely, (a, b) = (42 mm, 21 mm) and (18 mm, 4 mm) over the length 15-30 cm in beam direction.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF073  
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TUPMF074 Control of Collective Effects by Active Harmonic Cavity in an MBA-based Light Source with Application to the PETRA Upgrade cavity, emittance, lattice, synchrotron 1433
 
  • Y.-C. Chae, J. Keil
    DESY, Hamburg, Germany
 
  Based on the reference lattice for PETRA IV* we investigated collective effects with non-zero current. Out of many possibilities we firstly computed the intrabeam-scattering (IBS) effects on the emittance as well as lifetime as a function of current. The result indicated that PETRA IV would benefit from the reduced peak current when the harmonic cavity lengthens the bunch. The operating point of harmonic cavity was explored by tracking simulations as well as analytic formula. In order to compute the energy spread and bunch length we had used the known impedance function of the APS**. In this way more realistic estimation of IBS effects was expected. However, because of the complex nature of PETRA IV lattice, which includes achromatic cells for undulators, arc cells of octants and straight sectors for damping wigglers, we simplify the longitudinal dynamics by assuming the ring made of 92 multi-bend-achromat (MBA) cells. The optics is approximated as a linear-chromatic transfer map enabling fast tracking and the ring impedance is concatenated into the one location. The detailed collective effects with and without harmonic cavities are presented in the paper.
* J. Keil, "A PETRA IV Lattice Based on Hybrid Seven Bend Achromats", these proceedings.
** Y.-C. Chae and Y. Wang, "Impedance Database II for the Advanced Photon Source Storage Ring", Proc. PAC2007.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF074  
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TUPMK001 Removal of RF-Fingers at the Edges of the Injection Kickers resonance, kicker, storage-ring, injection 1485
 
  • T.F.G. Günzel, N. Ayala, F.F.B. Fernández, U. Iriso, M. Pont
    ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
 
  The ALBA storage ring injection kickers are equipped with RF-fingers to close a 2.5 mm gap between the ceramic tube and the metallic flange. After two distortion incidents that required the replacement of the fingers, their removal was decided. The decision could be supported by the observation that most of the additional impedance is created above the cut-off frequency of the beam pipe. This was later confirmed by a temperature decrease in that zone after the removal. Furthermore it was checked that the thresholds of the longitudinal coupled bunch instabilities of modes trapped around the resulting open gap are above the maximal applied beam current of 400 mA.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMK001  
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TUPMK010 Differences in Current Dependent Tune Shifts Measured by Direct or ORM Based Methods vacuum, storage-ring, optics, wakefield 1510
 
  • Y.E. Tan, R.T. Dowd
    AS - ANSTO, Clayton, Australia
 
  The change in the tunes as a function of total beam current is a well documented effect and has been attributed to quadrupole like self induced wakefields. Theoretical models presented by others have utilised direct methods (spectrum analyser) to measure the tunes in the analysis. In this report we shall present observations that show the ORM method, Linear Optics from Closed Optics (LOCO), and direct methods have significantly different tune gradients. The different tune gradients is attributed to the static (ORM) and dynamic (direct) nature of the measurements where in the static case the vacuum chamber is to be considered as a thin wall while in the dynamic case the vacuum chamber wall is to be considered as a thick wall.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMK010  
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TUPML003 Design of an L-band Accelerating Structure for the Argonne Wakefield Accelerator Facility Witness Beam Line Energy Upgrade linac, coupling, acceleration, quadrupole 1533
 
  • 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
 
  The Argonne Wakefield Accelerator (AWA) facility has been devoting much effort to the fundamental R&D of two-beam acceleration (TBA) technology with two parallel L-band beam lines. Beginning from the 70 MeV drive beam line, the high frequency (C-band and above) rf power is extracted from the beam by a decelerating structure (a.k.a. power extractor), transferred to an accelerating structure in the witness beam line, and used to accelerate the 15 MeV main beam. These high frequency accelerating structures usually have a small aperture to obtain high gradient and high efficiency, making it difficult for the low energy main beam to pass. To address this issue, one proposal is to increase the main beam energy to above 30 MeV by replacing the current witness linac. A 9-cell 𝜋-mode L-band standing-wave accelerating structure has therefore been designed to meet the high shunt impedance and low cost requirements. In addition, the single-feed coupling cell has been optimized with additional symmetrical ports to eliminate field distortion. The detailed design of the new accelerating structure will be presented in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML003  
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TUPML005 Study of a Dielectric Disk Structure for Short Pulse Two-Beam Acceleration acceleration, collider, beam-loading, 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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WEYGBE4 Low-Impedance Collimators for HL-LHC octupole, operation, collimation, luminosity 1794
 
  • S. A. Antipov, N. Biancacci, R. Bruce, A. Mereghetti, D. Mirarchi, E. Métral, S. Redaelli, B. Salvant
    CERN, Geneva, Switzerland
  • D. Amorim
    Université Grenoble Alpes, Grenoble, France
 
  The High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) will double its beam intensity for the needs of High Energy Physics frontier. This increase requires a reduction of the machine's impedance to ensure the coherent stability of the beams until they are put in collision. A major part of the impedance is the resistive wall contribution of the collimators. To reduce this contribution several coating options have been proposed. We have studied numerically the effect of the novel coatings on the beam stability. The results show that a decrease of up to 30% of the machine impedance and a reduction of up to 120 A in the stabilizing octupole current threshold can be achieved by coating the secondary collimators with Molybdenum. Half of that improvement can be obtained by coating the jaws of a subset of four collimators identified as the highest contributors to machine impedance. The installation of this subset of low-impedance collimators is planned for the Long Shutdown 2 in 2019-2020.  
slides icon Slides WEYGBE4 [5.724 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEYGBE4  
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WEPAF056 A Graphical User Interface for Transverse Bunch-by-Bunch Feedback at SPEAR3 feedback, interface, kicker, software 1951
 
  • K. Tian, W.J. Corbett, D.J. Martin, J.J. Sebek
    SLAC, Menlo Park, California, USA
  • Q. Lin
    Donghua University, Shanghai, People's Republic of China
  • D. Teytelman
    Dimtel, San Jose, USA
 
  Recently a transverse bunch-by-bunch feedback kicker was installed in SPEAR3 to control beam instabilities, remove unwanted satellite bunches and test resonant bunch excitation schemes for short pulse x-ray production. In conjunction with DIMTEL processing electronics, the feedback system can successfully stabilize undesirable beam modes and opens up the potential for more advanced investigations of bunch-by-bunch beam dynamics. To streamline the process, a graphical user interface was developed that allows the user to 'script' beam physics measurements from a single panel. At the press of a button the panel automatically downloads the measurement parameters, acquires the raw data and provides graphical displays of the beam response with calculated metadata. In this paper we present the interface format and examples of automated measurements.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAF056  
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WEPAL028 Study of the Influence of the CSR Impedance on the Synchronous Phase Shift at KARA synchrotron, simulation, storage-ring, radiation 2223
 
  • P. Schönfeldt, E. Blomley, M. Brosi, E. Bründermann, J. Gethmann, B. Kehrer, A.-S. Müller, A.I. Papash, J.L. Steinmann
    KIT, Karlsruhe, Germany
 
  Funding: This work has been supported by the German Federal Ministry of Education and Research (Grant No. 05K16VKA) and the Helmholtz Association (Contract No. VH-NG-320).
Measurements of the bunch current dependent synchronous phase shift are a standard method to characterize the impedance of a storage ring. To study this shift, different experimental approaches can be used. In this contribution, we first derive the phase shift caused by the impedance describing the emission of coherent synchrotron radiation (CSR) based on numerical simulations of the longitudinal phase space. The predicted shift is compared to measurement results obtained by time-correlated single photon counting.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL028  
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WEPAL049 Simulating Non-Relativistic Beams Using Helical Pulse Lines simulation, site, ECR, GUI 2288
 
  • C.J. Richard
    NSCL, East Lansing, Michigan, USA
  • S.M. Lidia
    FRIB, East Lansing, USA
 
  Funding: Work supported by the US Department of Energy, Office of Science, High Energy Physics under Cooperative Agreement award number DE-SC0018362.
Benchtop calibration of capacitive beam position monitors (BPMs) in low energy beamlines is challenging due to non-relativistic effects. Typical benchtop calibrations cannot account for these effects because they rely on speed of light fields transmitted along a straight wire. However, it is possible to replicate the electromagnetic fields generated by non-relativistic beams using a helical line pulse instead of a straight wire. In order to properly replicate the fields from a beam, a method must be developed for tailoring input pulses into the helical line to match bunch shape and a model of the impedance of the helix should be developed to assist with matching. This paper uses the sheath helix model to analyze signal propagation along a helical line in the time domain, with attention to dispersive effects and impedance matching. The results from this model are then compared to Microwave Studio simulations.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL049  
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WEPMF065 High Efficiency, High Power, Resonant Cavity Amplifier For PIP-II cavity, coupling, network, operation 2518
 
  • M.P.J. Gaudreau, N. Butler, D.B. Cope, P. H. Gordon, E.G. Johnson, M.K. Kempkes, R.E. Simpson
    Diversified Technologies, Inc., Bedford, Massachusetts, USA
 
  Funding: Funded under US DOE grant no. DE-SC0015780
Diversified Technologies, Inc. (DTI) is developing an integrated resonant-cavity combined solid-state amplifier for the Proton Improvement Plan-II (PIP-II) at Fermilab. The prototype has demonstrated multiple-transistor combining at 71% efficiency, at 675 watts per transistor at 650 MHz. The design simplifies solid-state transmitters to create straightforward scaling to high power levels. A crucial innovation is the reliable "soft-failure" mode of operation; a failure in one or more of these myriad combined transistors has negligible performance impact. The design couples the transistor drains directly to the cavity without first transforming to 50 Ohms, avoiding the otherwise-necessary multitude of circulators, cables, and connectors. DTI's design increases the power level at which it is cost-effective to employ a solid-state transmitter. DTI is upgrading the system to accommodate more transistors in each cavity module, and then will design and build a complete 100 kW-class transmitter which will consist of four such cavity modules and a combiner.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF065  
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WEPMF069 High Shunt Impedance Accelerating Structure with Distributed Microwave Coupling cavity, coupling, GUI, distributed 2531
 
  • S.P. Antipov, R.A. Kostin, S.V. Kuzikov
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • V.A. Dolgashev
    SLAC, Menlo Park, California, USA
 
  Funding: DOE SBIR
Conventional traveling wave or pi-phase advance standing wave structures use coupling of the microwave power through the beam pipe. This feature constrains the cavity shunt impedance (efficiency) to relatively small values. As microwave power flows through the accelerating cells in such structures, the probability of breakdown in high gradient operation is greatly increased. In this paper we present results from an accelerating structure prototype with distributed microwave coupling, an approach invented at SLAC. These structures include one or more parallel waveguides which are loaded by accelerating cavities. In this configuration accelerating cavities are fed independently and completely isolated at the beam pipe. Thus there is no microwave power flow through the accelerating cavity, making this geometry favorable for high gradient operation and maximizing the shunt impedance.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF069  
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WEPMF076 First Prototype Inductive Adder for the FCC Injection kicker, injection, distributed, high-voltage 2553
 
  • D. Woog, M.J. Barnes, A. Ferrero Colomo, J. Holma, T. Kramer
    CERN, Geneva, Switzerland
 
  A highly reliable kicker system is required as part of the injection for the FCC. A significant weak point of conventional kicker systems is often the pulse generator, where a Pulse Forming Network/Line (PFN/PFL) is discharged through a thyratron switch to generate the current pulse for the kicker magnet. This design has several disadvantages: in particular the occasional erratic turn-on of the switch which cannot be accepted for the FCC. A potential replacement is the inductive adder (IA) that uses semiconductor switches and distributed capacitors as energy storage. The modular design, low maintenance and high flexibility make the IA a very interesting alternative. In addition, the ability to both turn-on and off the current also permits the replacement of PFN/PFL by the capacitors. A first FCC prototype IA, capable of generating 9 kV and 2.4 kA pulses, has been designed and built at CERN. It will be upgrade to a full-scale prototype (15 kV, 2.4 kA) in 2018. This paper presents measurement results from the 9 kV prototype and outlines the conceptual changes and expected performance of the 15 kV prototype.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF076  
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WEPMF087 LHC Injectors Upgrade Project: Outlook of the Modifications to the Super Proton Synchrotron (SPS) Vacuum System and Impact on the Operation of the Carbon-Coated Vacuum Chambers vacuum, experiment, proton, extraction 2589
 
  • C. Pasquino, G. Bregliozzi, P. Chiggiato, P. Cruikshank, A. Farricker, A. Harrison, J. Perez Espinos, J.A.F. Somoza, M. Taborelli, C. Vollinger
    CERN, Geneva, Switzerland
 
  Aiming at doubling the beam intensity and reducing the beam emittance, significant modifications of the LHC and its injector chain will take place during Long Shutdown 2 (LS2), starting from 2019. The LIU project (LHC Injector Upgrade), in the specific, touches Linac4, the Proton Synchrotron Booster (PSB), the Proton Synchrotron (PS), the Super Proton Synchrotron (SPS) as well as the heavy ion chain. During LS2, important changes will take place mainly in the Long Straight Sections of the SPS to host a newly conceived dumping system, upgraded RF cavities and upgraded extraction channels. Additionally, the vacuum chambers of the main bending and focusing magnets as well as vacuum drifts will be coated with amorphous carbon in order to reduce the dynamic pressure effects induced by multipacting. The modifications to the different vacuum sectors will be described in details as well as the impact on operation of amorphous carbon coated sectors that have been already deposited.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF087  
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WEPMF089 Measurements of Electromagnetic Properties of Ferrites as a Function of Frequency and Temperature kicker, injection, coupling, simulation 2592
 
  • A. Chmielinska, M.J. Barnes, F. Caspers, B.K. Popovic, C. Vollinger
    CERN, Geneva, Switzerland
 
  Fast kicker magnets are used to inject beam into and extract beam out of the CERN accelerator rings. These kickers are often ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. The interaction of the beam with the resistive part of the longitudinal beam coupling impedance leads to power dissipation and heating of different elements in the accelerator ring. In particular, power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. In addition, the imaginary portion of the beam coupling impedance contributes to beam instabilities. A good knowledge of electromagnetic properties of materials up to GHz frequency range is essential for a correct impedance evaluation. This paper presents the results of transmission line measurements of complex initial permeability and permittivity for different ferrite types. We present an approach for deriving electromagnetic properties as a function of both frequency and temperature; this information is required for simulating ferrite behaviour under realistic operating conditions.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF089  
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WEPMK001 Preliminary Design of a Cooling System for the LHC Injection Kicker Magnets kicker, injection, vacuum, operation 2624
 
  • L. Vega Cid, M.J. Barnes, L. Ducimetière, M.T. Moester, V. Vlachodimitropoulos, W.J.M. Weterings
    CERN, Geneva, Switzerland
  • A. Abánades
    ETSII UPM, Madrid, Spain
 
  The CERN Large Hadron Collider (LHC) is equipped with two fast pulsed magnet systems (MKIs) that inject particle beams from the injector chain. Future operation for High Luminosity LHC (HL-LHC) with high intensity beams will cause heating of the ferrite yokes of the MKIs beyond their Curie temperature, preventing injection until the yokes cool down. Beam coupling impedance studies show that it is possible to move a substantial portion of the beam induced power deposition from the upstream ferrite yokes, which are the yokes with the highest power deposition, to ferrite rings located at the upstream end of the magnet. Thermal predictions show that this power redistribution, combined with the installation of a cooling system around the rings, will maintain the temperatures of all the yokes and ferrite rings below their Curie point. Since the rings are not pulsed to high voltage, whereas the ferrite yokes are, the installation of a cooling system is feasible around the rings. The proposed design of the cooling system will be tested to ensure good performance before its installation on the MKIs. The details of the simulations and the design process are reported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMK001  
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WEPMK002 Longitudinal Impedance Analysis of an Upgraded LHC Injection Kicker Magnet kicker, simulation, injection, vacuum 2628
 
  • V. Vlachodimitropoulos, M.J. Barnes, L. Vega Cid, W.J.M. Weterings
    CERN, Geneva, Switzerland
 
  Prior to Long Shutdown 1 (LS1) one of the LHC injection kickers (MKIs) occasionally exhibited high temperatures leading to significant turnaround times. After a successful impedance mitigation campaign during LS1, the MKI ferrite yokes have remained below their Curie point and have not limited LHC's availability. However, for HL-LHC operation the MKI yokes are expected to exceed their Curie temperatures after long physics runs. To ensure uninterrupted future HL-LHC operation, a modified beam screen design, relocating some of the heat load to more easily cooled parts, and a suitable cooling system are under development as the current baseline for the HL-LHC upgrade of the MKIs. An upgraded beam screen providing such relocation has been designed, simulated and compared to the existing model. To validate simulations, two longitudinal beam coupling impedance measurement techniques have been used and the results are compared to predictions. The modified beam screen was implemented in an upgraded MKI installed in the LHC during the Year End Technical Stop (YETS) 2017/18.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMK002  
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WEPMK003 An Upgraded LHC Injection Kicker Magnet kicker, injection, vacuum, electron 2632
 
  • M.J. Barnes, C. Bracco, G. Bregliozzi, A. Chmielinska, L. Ducimetière, B. Goddard, T. Kramer, H. Neupert, L. Vega Cid, V. Vlachodimitropoulos, W.J.M. Weterings, C. Yin Vallgren
    CERN, Geneva, Switzerland
  • A. Chmielinska
    EPFL, Lausanne, Switzerland
 
  Funding: Work supported by the HL-LHC project.
An upgrade of the LHC injection kickers is necessary for HL-LHC to avoid excessive beam induced heating of these magnets: the intensity of the HL-LHC beam will be twice that of LHC. In addition, in the event that it is necessary to exchange an injection kicker magnet, the newly installed kicker magnet would limit HL-LHC operation for a few hundred hours due to dynamic vacuum activity. Extensive studies have been carried out to identify practical solutions to these problems: these include redistributing a significant portion of the beam induced power deposition to ferrite parts of the kicker magnet which are not at pulsed high voltage and water cooling of these parts. Furthermore a surface coating, to mitigate dynamic vacuum activity, has been selected. The results of these studies, except for water cooling, have been implemented on an upgraded LHC injection kicker magnet: this magnet was installed in the LHC during the 2017-18 Year End Technical Stop. This paper presents the upgrades, including some test and measurement results.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMK003  
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WEPMK005 Preliminary Results from Validation Measurements of the Longitudinal Power Deposition Model for the LHC Injection Kicker Magnet kicker, injection, coupling, operation 2636
 
  • V. Vlachodimitropoulos, M.J. Barnes, A. Chmielinska
    CERN, Geneva, Switzerland
  • A. Chmielinska
    EPFL, Lausanne, Switzerland
 
  During Run 1 of the LHC, one of the injection kicker magnets (MKIs) exhibited an excessively high ferrite temperature, caused by coupling of the high intensity beam to the real impedance of the magnet. Beam-screen upgrades, implemented during Long Shutdown 1 (LS1), have been very effective in reducing beam coupling impedance and since then the MKIs have not limited LHC's availability. However, temperature measurements during operation have shown that one end of the MKI's ferrite yoke is consistently hotter than the other. Detailed simulation models and data post-processing algorithms have been developed to understand and mitigate the observed behaviour. In the present paper, the model used to obtain the power loss distribution along the magnet is presented. The model is subsequently applied to two MKI design configurations under study: (i) the one currently in operation and (ii) an upgraded magnet that was installed in the LHC tunnel during the Year End Technical Stop (YETS) 2017/18. In order to validate the expected behaviour a novel measurement technique was developed, applied in both configurations and compared to predictions. The results obtained are reported and conclusions regarding the effectiveness of the design are drawn.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMK005  
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WEPML003 Precision Q0 Measurement of an SRF Cavity with a Digital RF Techniques cavity, coupling, SRF, GUI 2674
 
  • J.P. Holzbauer, B.M. Hanna, Y.M. Pischalnikov, W. Schappert, D.A. Sergatskov, A.I. Sukhanov
    Fermilab, Batavia, Illinois, USA
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Direct measurement of the quality factor of SRF cavity using traditional RF techniques is essential for cavity production and development. Systematic effects of the measurement can contribute significant amounts of error to these measurements if not accounted for. This paper will present measurements taken at Fermilab using a digital RF system to characterize and correct for these systematic effects and directly measure the quality factor versus gradient curve for a single spoke resonator in the Spoke Test Cryostat at Fermilab. These measurements will be compared to traditional calorimetric measurements, and a discussion of improving/extending these techniques to other testing situations will be included.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML003  
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WEPML012 Progress on the Construction of the Perpendicularly Biased 2nd Harmonic Cavity for the Fermilab Booster cavity, HOM, booster, damping 2703
 
  • R.L. Madrak, J.E. Dey, K.L. Duel, M.R. Kufer, J. Kuharik, A.V. Makarov, R.D. Padilla, W. Pellico, J. Reid, G.V. Romanov, M. Slabaugh, D. Sun, C.-Y. Tan, I. Terechkine
    Fermilab, Batavia, Illinois, USA
 
  A perpendicularly biased tuneable 2nd harmonic cavity, designed for the Fermilab Booster, is being assembled for testing this summer (2018). The cavity will work at twice the frequency of the fundamental cavities, and will be on only during the injection and transition (or extraction) periods. The main purpose of adding this cavity is to improve beam capture and reduce losses as required by Fermilab's Proton Improvement Plan (PIP). After three years of testing and optimization, the cavity design has now been finalized and all constituent parts have been received. We report on the cavity final design and on the status of the construction.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML012  
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WEPML021 First Performance Results of the PIP2IT MEBT 200 Ω Kicker Prototype kicker, booster, ISOL, target 2724
 
  • G.W. Saewert, M.H. Awida, B.E. Chase, A.Z. Chen, J. Einstein-Curtis, D. Frolov, K.S. Martin, H. Pfeffer, D. Wolff
    Fermilab, Batavia, Illinois, USA
  • S. Khole
    BARC, Trombay, Mumbai, India
  • D. Sharma
    RRCAT, Indore (M.P.), India
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics
The PIP-II project is a program to upgrade the Fermilab accelerator complex. The PIP-II linac includes a 2.1 MeV Medium Energy Beam Transport (MEBT) section that incorporates a unique chopping system to perform arbi-trary, bunch-by-bunch removal of 162.5 MHz structured beam. The MEBT chopping system will consist of two identical kickers working together and a beam absorber. One design of two having been proposed has been a 200 Ω characteristic impedance traveling wave dual-helix kicker driven with custom designed high-speed switches. This paper reports on the first performance results of one prototype kicker built, installed and tested with beam at the PIP-II Injector Test (PIP2IT) facility. The helix deflector design details are discussed. The electrical performance of the high-speed switch driver operating at 500 V bias is presented. Tests performed were chopping beam at 81.25 MHz for microseconds as well as with a truly arbitrary pattern for 550 us bursts having a 45 MHz average switching rate and repeating at 20 Hz.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML021  
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WEPML031 The New Broadband Accelerating System for the SIS18 Upgrade at GSI cavity, operation, controls, resonance 2755
 
  • P. Hülsmann, R. Balß, H. Klingbeil, U. Laier, K.-P. Ningel, C. Thielmann, B. Zipfel
    GSI, Darmstadt, Germany
 
  In this contribution, a new SIS18 rf accelerating system is presented whose cavities are based on magnetic alloy materials. The rf system works at harmonic number h=2 (f=0,43- to 2,8 MHz) and provides the necessary accelerating voltage (up to 50kVp) for SIS18 injector operation for FAIR with high intensity heavy ion beams in a fast operation mode with up to three cycles per second. The paper focusses on the cavity part and its cooling issues as well as the broadband characteristics. Due the lossy magnetic alloy ring core filling, which consists of high permeability Finemet FT3M ring cores (HITACHI), the cavities show a broadband behaviour and thus no cavity tuning during the acceleration ramp is necessary. To keep the bandwidth of the cavities as broad as possible they are cooled by a special mineral oil with low permittivity. Also the beam impedance and the power consumption of the rf system are discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML031  
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WEPML043 RF Simulations of the Injector Section from CH8 to CH15 for MYRRHA simulation, cavity, resonance, MMI 2790
 
  • P. Müller, M. Busch, H. Hähnel, K. Kümpel, D. Mäder, N.F. Petry, H. Podlech
    IAP, Frankfurt am Main, Germany
 
  Funding: Work supported by the EU Framework Programme H2020 662186 (MYRTE) and HIC for FAIR
MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is the first prototype of an accelerator driven nuclear reactor dealing with the transmutation of long-living nuclear waste. Beam quality and reliability are crucial for the reactor. The injector design is done by IAP, Goethe-University, and has been adapted to the final magnet design and voltage distributions. The energy section from 5.87 MeV up to 16.6 MeV has been changed to normal conducting CH cavities as in the lower energy part of the injector. For beam adjustment a 5-gap CH cavity rebuncher at 5.87 MeV as well as two doublet magnets forming the new MEBT-2 section between CH7 and CH8 have been added. Starting parameters for the RF simulations have been given by beam dynamics results calculated with LORASR. RF simulations of these structures consisting of flatness and tuning optimizations will be presented within this contribution.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML043  
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WEPML055 Simulation Study of Parasitic-Mode Damping Methods for a 1.5-GHz TM020-Mode Harmonic Cavity cavity, damping, coupling, radiation 2822
 
  • N. Yamamoto, S. Sakanaka, T. Takahashi
    KEK, Ibaraki, Japan
 
  Design study of parasitic-mode (PM) damped structures has been conducted for the purpose to realize a normal conducting 1.5 GHz harmonic cavity which is based on the TM020 resonant mode*. We have investigated the performances of two PM-damping mechanisms, that are, rod-type antennas** and annular slots. The rod-type antennas locate at the node of electric field of the TM020 mode while the annular slots locate at the node of magnetic field. As a result of 3D electromagnetic simulations, suitable performances of PMs were confirmed by employing either of the PM-damping mechanisms. It was also shown that the slot-type structure is superior in PM-damping performance and in the unloaded Q of the TM020 mode.
* N. Yamamoto et al., IPAC'17, paper THOPIK037; N. Yamamoto Phys. Rev. Accel. Beams, 21, 1, 012001.
** T. Takahashi et al., IPAC'17, paper THPIK036.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML055  
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WEPML069 Fast Kicker and Pulser R&D for the HEPS on-Axis Injection System kicker, injection, vacuum, simulation 2846
 
  • H. Shi, J. Chen, Z. Duan, L. Huo, P. Liu, X.L. Shi, G. Wang, L. Wang, N. Wang
    IHEP, Beijing, People's Republic of China
 
  The HEPS plans to adopt on-axis injection scheme because the dynamic aperture of machine is not large enough for off-axis injection for its baseline 7BA lattice design. A sets of super fast kicker and pulser of ±15kV amplitude, 15ns pulse bottom width are needed for bunch spacing of 10ns to minimize perturbation on adjacent bunches. To achieve these requirement, a multifaceted R&D program including the strip-line kicker and HV pulser, was initiated last 2 years. So far, the prototype development of a 750mm long strip-line kicker and a DSRD pulser was completed and the preliminary test results show they can meet the baseline requirement of the HEPS.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML069  
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WEPML071 Superconducting 16-Pole Wiggler for Beijing Electron-Positron Collider II wiggler, vacuum, collider, positron 2853
 
  • M.X. Li, X.J. Bian, F.S. Chen, W. Chen, X.J. Sun, H. Wang, J.L. Wang, N. Wang, M.F. Xu, X.C. Yang
    IHEP, Beijing, People's Republic of China
 
  A superconducting 16-pole 2.6T wiggler with period 170mm of The High-Energy Photon Source and the Test Facility Project (HEPS-TF) designed and fabricating in the Institute of High Energy Physics (IHEP) in China is described. This wiggler will be installed in Beijing Electron-Positron Collider II (BEPCII). The main parameters and structure of the wiggler are presented. Besides, some vertical testing results are involved.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML071  
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THPAF014 Studies of the Single-Bunch Instabilities in the Booster of HEPS booster, storage-ring, lattice, injection 2971
 
  • H.S. Xu, Z. Duan, J.L. Li, Y.M. Peng, S.K. Tian, N. Wang
    IHEP, Beijing, People's Republic of China
 
  High Energy Photon Source (HEPS), which is proposed in China, is an ultra-low emittance storage ring based synchrotron light source. Because of the requirement of the relatively high single-bunch charge, the booster may suffer from the single-bunch instabilities. A preliminary impedance model has been developed for the studies of collective instabilities in the booster. Based on this impedance model, the longitudinal and transverse single-bunch instabilities have been studied.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF014  
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THPAF020 Measurement of Transverse Impedance of Specific Components in CESR Using BPM Measurements of Pinged Bunches undulator, cavity, experiment, betatron 2990
 
  • M.P. Ehrlichman, J.P. Shanks, S. Wang
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  A beam-based technique is applied to determine the quadrupole impedance of large-impedance components of the CESR storage ring. Two bunches separated by ~1/3 of the ring circumference are charged to 0.85 and 0.3 mA. Each bunch is given a single kick, either horizontal or vertical. Turn-by-turn, bunch-by-bunch position information is recorded for ~16 k turns. BPM-by-BPM phase is calculated using the All-phase FFT method of spectral analysis. The difference in the BPM-to-BPM phase advance between the two bunches is a measurement of the local transverse impedance. The impedances of the small-aperture in-vacuum undulators, collimators, scrapers, RF cavities, electrostatic separators, and bulk impedance of the remaining ring are determined in this manner.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF020  
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THPAF034 Studies of Horizontal Instabilities in the CERN SPS simulation, octupole, optics, damping 3032
 
  • M.S. Beck, H. Bartosik, M. Carlà, K.S.B. Li, G. Rumolo, M. Schenk
    CERN, Geneva, Switzerland
  • U. van Rienen
    Rostock University, Faculty of Engineering, Rostock, Germany
 
  In the framework of the LHC Injectors Upgrade (LIU), beams with double intensity with respect to the present values will have to be successfully accelerated by the CERN Super Proton Synchrotron (SPS) and extracted towards the Large Hadron Collider (LHC). However, first experience running with intensity higher than the nominal LHC beam has shown that coherent instabilities in the horizontal plane may develop, becoming a potential intensity limitation for the future high intensity operation. To understand the mechanism of these instabilities, the PyHEADTAIL code has been used to check if the SPS impedance model reproduces the observations. The instability growth rates have been studied for different machine models and different chromaticity settings. In addition, the effect of other stabilizing methods, like the octupoles and the transverse damper, has also been investigated. Measurements are presented to benchmark the simulations.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF034  
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THPAF035 Single-Collimator Tune Shift Measurement of the Three-Stripe Collimator at the LHC octupole, luminosity, feedback, hadron 3036
 
  • S. A. Antipov
    University of Chicago, Chicago, Illinois, USA
  • D. Amorim, N. Biancacci, L.R. Carver, G. Mazzacano, A. Mereghetti, E. Métral, S. Redaelli, B. Salvant, D. Valuch
    CERN, Geneva, Switzerland
 
  Several options of low resistivity coating have been proposed for the collimator upgrade of the Large Hadron Collider. In order to study their effect on the beam dynamics a special collimator has been built and installed in the machine. Its jaws are coated with three different materials and can be moved transversely to selectively expose the beam to the chosen coating. We have measured the resistive wall tune shifts of each coating material and compared them with that of a standard Carbon Fibre Composite (CFC) collimator jaw. A resolution of the tune shift of the order of 10-5 has been achieved in the measurement. The results show a significant reduction of the resistive wall tune shift with novel materials. The largest improvement is obtained with a 5 μm Molybdenum coating of a Molybdenum-Graphite jaw. The observed tune shifts show a good agreement with the impedance model and the bench impedance and resistivity measurements. Obtained results can be used to further improve the precision of the impedance model.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF035  
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THPAF036 Longitudinal and Quadrupolar Coupling Impedance of an Elliptical Vacuum Chamber With Finite Conductivity in Terms of Mathieu Functions vacuum, coupling, factory, electromagnetic-fields 3040
 
  • M. Migliorati, L. Palumbo
    Sapienza University of Rome, Rome, Italy
  • N. Biancacci
    CERN, Geneva, Switzerland
  • M. Migliorati, L. Palumbo
    INFN-Roma1, Rome, Italy
  • V.G. Vaccaro
    Naples University Federico II and INFN, Napoli, Italy
 
  Funding: Work supported by the CERN PS-LIU project
The resistive wall impedance of an elliptical vacuum chamber in the classical regime with infinite thickness is known analytically for ultra-relativistic beams by means of the Yokoya form factors. Starting from the longitudinal electric field of a point charge moving at arbitrary speed in an elliptical vacuum chamber, which we express in terms of Mathieu functions, in this paper we take into account the finite conductivity of the beam pipe walls and evaluate the longitudinal and quadrupolar impedance for any beam velocity. We also obtain that the quadrupolar impedance of a circular pipe is different from zero, approaching zero only for ultra-relativistic particles. Even if some of the results, in particular in the ultra-relativistic limit, are already known and expressed in terms of form factors, this approach is the first step towards the calculation of the general problem of a multi-layer vacuum chamber with different conductivities and of elliptic cross section.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF036  
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THPAF041 Uncontrolled Longitudinal Emittance Blow-Up during RF Manipulations in the CERN PS cavity, emittance, simulation, controls 3056
 
  • A. Lasheen, H. Damerau, G. Favia
    CERN, Geneva, Switzerland
 
  The CERN Proton Synchrotron (PS) determines the basic bunch spacing for the Large Hadron Collider (LHC) by means of rf manipulations. Several rf systems in a frequency range from 2.8 MHz to 200 MHz are available for beam acceleration and manipulations. Each of the six bunches injected from the PS Booster is split in several steps into 12 bunches spaced by 25 ns, yielding a batch of 72 bunches at transfer to the Super Proton Synchrotron (SPS). In the framework of the LHC Injector Upgrade (LIU) project the bunch intensity must be doubled. However, with most of the planned upgrades already in place this intensity has not yet been achieved due to collective effects. One of them is uncontrolled longitudinal emittance blow-up during the bunch splittings. In this contribution, measurements of the blow-up during the splitting process are presented and compared with particle simulations using the present PS impedance model. Beam-based measurements of the impedances of the rf cavities have been performed. They revealed that to reproduce the instability an additional impedance source is required in the PS impedance model.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF041  
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THPAF048 Destabilising Effect of the LHC Transverse Damper coupling, damping, feedback, synchrotron 3076
 
  • E. Métral, D. Amorim, S. A. Antipov, N. Biancacci, X. Buffat, K.S.B. Li
    CERN, Geneva, Switzerland
 
  Three questions motivated this study for the CERN Large Hadron Collider in terms of beam stability: (i) why a chromaticity close to zero seemed more critical than predicted during Run 1 (in 2011 and 2012) and during Run 2 (in 2015)?; (ii) why some past simulations with a chromaticity close to zero revealed a more critical situation with the transverse damper than without?; (iii) what should be the minimum operational chromaticity in the future in the LHC and High-Luminosity LHC? A new Vlasov solver (called GALACTIC) was developed to shed light on the destabilising mechanism of the transverse damper, which is a potential contributor to explain the LHC observation. Due to the features, which are discussed in this paper, the name 'ISR (for Imaginary tune Split and Repulsion) instability' is suggested for this new kind of single-bunch instability with zero chromaticity.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF048  
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THPAF051 Beam Impedance Evaluation for CERN PS Gate Valves by Simulation and Benchmark Measurement simulation, wakefield, resonance, coupling 3080
 
  • B.K. Popovic, C. Vollinger
    CERN, Geneva, Switzerland
 
  The CERN High Luminosity LHC project calls for a doubling of beam intensity which requires a clear identification of possible longitudinal instability sources in the injector chain. This requirement yields the need to further improve the longitudinal impedance model for the Proton Synchrotron (PS). In this impedance model it is necessary to include not only obvious impedance sources, such as RF cavities and kickers but also seemingly innocuous elements like certain vacuum components. Individually these vacuum elements would give only a small impedance contribution, however, due to the large number of these elements in the machine, their resultant combined impedances impact the overall impedance budget. This paper presents the electromagnetic simulation analysis of the PS sector gate valves along with EM measurements confirming the simulation model. These measurements are especially crucial in this case since no complete mechanical model or drawings are available and assumptions had to be made regarding its interior mechanical structure.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF051  
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THPAF052 Impedance Analysis of New PS Internal Dump Design HOM, coupling, resonance, vacuum 3083
 
  • B.K. Popovic, L. Teofili, C. Vollinger
    CERN, Geneva, Switzerland
 
  The High Luminosity Large Hadron Collider (HL-LHC) project at CERN calls for increasing beam intensity in the injector chain. In the Proton Synchrotron (PS), a pre-injector of the LHC, these intensities can result in beam instabilities and potential RF heating of machine components, such that impedance mitigation measures are required. To study these intensity effects, the PS impedance model has been developed and is continuously updated. Each new machine element that is to be added into the accelerator requires an impedance study to minimize its contribution with respect to the machine's overall impedance budget. In such a context, this paper presents the impedance analysis of the new design of the internal beam dump for the PS, showing the design process required to reduce the impedance contribution of this element. Furthermore, the impedance analysis of the currently installed beam dump is analysed in order to compare the impedance contributions of the two designs.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF052  
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THPAF053 Lower-Harmonic RF System in the CERN SPS emittance, simulation, cavity, proton 3087
 
  • J. Repond, H. Damerau, A. Lasheen, E.N. Shaposhnikova
    CERN, Geneva, Switzerland
 
  Significant beam losses increasing with intensity are observed at capture and along the SPS flat bottom for the LHC-type proton beam. The intensity should be doubled for HL-LHC and high losses may be a major performance limitation. Bunches extracted from the PS, the SPS injector, are produced in a 40 MHz RF system applying a bunch rotation at the end of the cycle and therefore cannot be perfectly matched to the 200 MHz SPS RF bucket. The possibility of using a lower harmonic additional RF capture system in the SPS was already proposed after the LEP era in preparation for transfer of the LHC beam but the bunch rotation was the preferred solution, since the induced voltage in the SPS 200 MHz RF system would be too large to ensure stability in a low harmonic system without mitigation measures. However, the use of the upgraded one-turn feedback and the 200 MHz RF system as a Landau cavity could help to improve stability. The feasibility of this scenario to reduce capture losses in the SPS is analysed and presented in this paper. The choice of an optimum RF frequency and voltage is also discussed. The transfer to the main 200 MHz is simulated using a realistic bunch distribution.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF053  
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THPAF063 Identification of Imperfections in Impedance Shields on the SPS-QF Flanges via Non-Intrusive Measurements resonance, shielding, coupling, cavity 3119
 
  • A. Farricker, P. Kramer, B.K. Popovic, E. Sunar, C. Vollinger, M. Wendt
    CERN, Geneva, Switzerland
 
  In order to achieve the highest beam intensities possible in the LHC the highest quality beam possible has to be supplied by the injector chain. The Super Proton Synchrotron (SPS) at CERN is the last accelerator in the injector chain of the LHC. One factor that is currently known to limit the intensity of the beam for injection to the LHC, is the longitudinal beam-coupling impedance in the SPS. One known source of multi-bunch instability is the vacuum flanges and campaigns to mechanically shield this source were completed in the year 2000. However, today it cannot be excluded that some of these shields may have partial or indeed full failures. Since these flanges are next to a QF magnet and are in most cases connected to a BPH (Beam Position Monitor Horizontal), it is possible to carry out via the BPH an in-situ measurement of the effectiveness of the shields. In this paper we present a methodology as well as measurement results taken with this non-intrusive in-situ method. From measurements, it is possible to identify if the flanges are without any impedance shield, equipped with either a fully functioning shield or a shield exhibiting non-ideal properties.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF063  
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THPAF079 Landau Damping and Tune-Spread Requirements for Transverse Beam Stability octupole, simulation, damping, quadrupole 3168
 
  • V. Kornilov, O. Boine-Frankenheim
    GSI, Darmstadt, Germany
 
  Passive mitigation methods are effective cures for collective instabilities in ring accelerators. For decades, octupole magnets have been used as an established and well-understood passive mitigation method. Present and the future accelerator facilities, like FAIR or FCC, impose new challenges on the passive mitigation due to higher energies and smaller beam emittances. Lattice resonances usually restrict the tolerable tune-spreads which are essential for the passive mitigation methods. We study the stability of transverse bunch oscillations provided by octupole magnets and radio-frequency quadrupoles. The special focus of our study is on the interplay and role of decoherence, phase-mixing and Landau damping for the different mitigation schemes. Particle tracking simulations are performed and the tune spreads for the different mechanisms are compared with each other and also with analytical dispersion relations.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF079  
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THPAK001 Impedance Evaluation of In-Vacuum Undulator at KEK Photon Factory simulation, undulator, factory, vacuum 3200
 
  • O. Tanaka, M. Adachi, R. Kato, N. Nakamura, T. Obina, S. Sakanaka, R. Takai, K. Tsuchiya, N. Yamamoto
    KEK, Ibaraki, Japan
 
  The estimate of impedance and kick factors of the recently installed at KEK Photon Factory (PF) four In-Vacuum Undulators (IVU) is currently a very important issue, because they could be considerable contributors to the total impedance of PF. Moreover, the coupling impedance of the IVUs could lead to the beam energy loss, changes in the bunch shape, betatron tune shifts and, finally, to the various beam instabilities. Using the simulation tool (CST Particle Studio), longitudinal and transverse impedances of the IVUs were evaluated and compared to analytical formulas and measurement results. The study provides guidelines for mitigation of unwanted impedance, for the accurate estimate of its effects on the beam quality and beam instabilities and also for the impedance budget of a newly designed next-generation machine which has many IVUs and small-aperture beam pipes.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK001  
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THPAK002 Updated Model of the Resistive Wall Impedance for the Main Ring of J-PARC space-charge, kicker, hadron, injection 3204
 
  • B. Yee-Rendón, Y.H. Chin, H. Kuboki, T. Toyama
    KEK, Ibaraki, Japan
  • M. Schenk
    CERN, Geneva, Switzerland
 
  The resistive wall impedance is one of the major contributors of the impedance in the Main Ring of J-PARC. The present model assumes round chambers of stainless steel with perfect magnet boundary conditions for its surroundings. This work presents the model of the resistive wall impedances taking into account the different chamber geometries of Main Ring, the materials and more realistic surroundings. The models were benchmarked with measurements of the coherent tune shift of the Main Ring of J-PARC. The simulation of beam instabilities is a helpful tool to evaluate potential threats against the machine protection of the high intensity beams.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK002  
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THPAK005 Measuring the Coupling Impedance of Vacuum Components for the Advanced Photon Source Upgrade Using a Goubau Line cavity, simulation, vacuum, coupling 3211
 
  • M.P. Sangroula
    IIT, Chicago, Illinois, USA
  • R.M. Lill, R.R. Lindberg, R.B. Zabel
    ANL, Argonne, Illinois, USA
 
  The Planned upgrade of the Advanced Photon Source to a multi-bend achromat (MBA) will increase the x-ray brightness by two to three orders of magnitude. Storing such an intense beam stably inside the narrow gap vacuum chambers requires sophisticated and appropriately designed rf-components that helps to minimize rf heating and collective instabilities associated with the impedance of these small-aperture vacuum components. As part of this effort, my research focuses on impedance measurement and simulation of various MBA vacuum components. In this paper, we briefly introduce the novel Goubau line (G-line) test fixture for the impedance measurement, at first, and then present our measurements data along with simulations with simulations for various vacuum components designed for the APS Upgrade.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK005  
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THPAK015 Impedance and Heat Load Analysis of the Stripline Kicker in HEPS kicker, simulation, coupling, injection 3234
 
  • N. Wang, J. Chen, Z. Duan, H. Shi, S.K. Tian, L. Wang, H.S. Xu
    IHEP, Beijing, People's Republic of China
 
  In the High Energy Photon Source (HEPS), strip-line kickers are adopted for beam injection and extraction. Beam coupling impedance contribution from the strip-line kicker is calculated. Detailed studies on the heat load dissipation have been performed. The peak electric field on the blade and the induced voltage on the feedthroughs due to the beam passage are also calculated.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK015  
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THPAK016 Measurement and Analysis of Synchrotron Tune Variation with Beam Current in BEPCII synchrotron, cavity, positron, electron 3237
 
  • N. Wang, Z. Duan, G. Xu, H.S. Xu, C.H. Yu, Y. Zhang
    IHEP, Beijing, People's Republic of China
 
  Coherent synchrotron frequency shift is observed during machine studies in BEPCII (Beijing Electron Positron Collider Upgrade). The results show that the synchrotron frequency varies parabolically with the increase of the beam current. This phenomenon is supposed to be induced by the interaction of the beam with the fundamental mode of the accelerating cavity. In order to explain this phenomenon, a simple physical model is developed from the couple bunch instability theory. The analytical estimations based on the physical model show good agreement with the measurements.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK016  
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THPAK037 Beam-Loading Transients and Bunch Shape in the Operation of Passive Harmonic Cavities in the ALS-U cavity, simulation, beam-loading, 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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THPAK052 Single Bunch Instabilities in FCC-ee collider, simulation, electron, vacuum 3336
 
  • E. Belli
    Sapienza University of Rome, Rome, Italy
  • G. Castorina, M. Migliorati
    INFN-Roma1, Rome, Italy
  • G. Rumolo
    CERN, Geneva, Switzerland
  • B. Spataro, M. Zobov
    INFN/LNF, Frascati (Roma), Italy
 
  FCC-ee is a high luminosity lepton collider with a centre-of-mass energy from 91 to 365 GeV. Due to the machine parameters and pipe dimensions, collective effects due to electromagnetic fields produced by the interaction of the beam with the vacuum chamber can be one of the main limitations to the machine performance. In this frame, an impedance model is required to analyze these instabilities and to find possible solutions for their mitigation. This paper will present the contributions of specific machine components to the total impedance budget and their effects on the beam stability. Single bunch instability thresholds will be estimated in both transverse and longitudinal planes.   
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK052  
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THPAK055 Suppression of Transverse Beam Instabilities by Stripline Kickers at TPS kicker, feedback, damping, storage-ring 3346
 
  • P.J. Chou, C.K. Chan, C.-C. Chang, K.T. Hsu, K.H. Hu, C.K. Kuan, I.C. Sheng, F.H. Tseng
    NSRRC, Hsinchu, Taiwan
 
  Collective beam instabilities could limit the accelerator performance if proper countermeasures are not in place. Active beam feedback systems are commonly used to suppress beam instabilities. The resistive wall impedance including phase-II insertion devices at TPS are calculated with analytical formulas. The growth rate of transverse coupled bunch instabilities due to wall impedance is estimated by theory. The RF properties of existing stripline kickers in TPS are analyzed with a 3-D electromagnetic simulation code GdfidL. Based on the above analysis, the requirements for a beam feedback system are calculated and the results are reported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK055  
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THPAK070 Coupled Bunch Instability from JLEIC Crab Cavity Higher Order Modes cavity, HOM, luminosity, feedback 3392
 
  • S.I. Sosa Guitron, S.U. De Silva, J.R. Delayen, H. Park
    ODU, Norfolk, Virginia, USA
  • R. Li, V.S. Morozov, H. Park
    JLab, Newport News, Virginia, USA
 
  Particle bunches traveling in a ring can excite wakefields inside any radio-frequency element present. These electromagnetic modes can resonate long enough and interact with subsequent passing bunches. A coherent oscillation between bunches can quickly become an instability and needs to be addressed. The Jefferson Lab electron ion collider has a large 50 mrad crossing angle and thus relies on bunch crabbing to achieve high luminosity. Bunch crabbing is done with compact superconducting rf dipole cavities. We study coupled bunch oscillations driven by the higher order modes of multicell RFD crab cavities under study for JLEIC, we calculate the instability growth time assuming a symmetric beam spectrum, identify the HOMs driving the instability and discuss mitigation measures.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK070  
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THPAK077 Feasibility of Non-Metal Vacuum Chamber for Storage Rings vacuum, cavity, insertion-device, insertion 3411
 
  • T.-Y. Lee
    PAL, Pohang, Kyungbuk, Republic of Korea
 
  This paper studies if the vacuum chamber of an elec-tron storage ring can be made of dielectric non-meta materials such as ceramics or glass. The purpose of this study is to substantially reduce the broadband imped-ance of the vacuum chamber and consequently mitigate single bunch instabilities. This theoretical study examines how these materials can reduce the impedance and pro-poses how to resolve technical problems to occur.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK077  
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THPAK091 Design of the New Proton Synchrotron Booster Absorber Scraper (PSBAS) in the Framework of the Large Hadron Collider Injection Upgrade (LIU) Project vacuum, proton, simulation, booster 3444
 
  • L. Teofili, M. Migliorati
    Sapienza University of Rome, Rome, Italy
  • J.A. Briz Monago, M. Calviani, N. Chritin, J.J. Esala, S.S. Gilardoni, I. Lamas Garcia, J. Maestre, T. Polzin, T.L. Rijoff
    CERN, Geneva, Switzerland
  • T.L. Rijoff
    TU Darmstadt, Darmstadt, Germany
 
  The Large Hadron Collider (LHC) Injector Upgrade (LIU)Project at CERN calls for increasing beam intensity for the LHC accelerator chain. Some machine components will not survive the new beam characteristics and need to be rebuilt for the new challenging scenario. This is particularly true for beam intercepting devices (BIDs) such as dumps, collimators, and absorber/scrapers, which are directly exposed to beam impacts. In this context, this work summarizes conceptual design studies on the new Proton Synchrotron Booster (PSB) Absorber/Scraper (PSBAS), a device aimed at cleaning the beam halo at the very early stage of the PSB acceleration. This paper outlines the steps performed to fulfil the component design requirements. It discusses thermo-mechanical effects as a consequence of the beam-matter collisions, simulated with the FLUKA Monte Carlo code and ANSYS finite element software; and the impedance minimization study performed to prevent beam instabilities and to reduce RF-heating on the device.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK091  
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THPAK092 Analysis on the Mechanical Effects Induced by Beam Impedance Heating on the HL-LHC Target Dump Injection Segmented (TDIS) Absorber injection, simulation, HOM, shielding 3448
 
  • L. Teofili, M. Migliorati
    Sapienza University of Rome, Rome, Italy
  • M. Calviani, D. Carbajo Perez, S.S. Gilardoni, F. Giordano, I. Lamas Garcia, G. Mazzacano, A. Perillo-Marcone
    CERN, Geneva, Switzerland
 
  The High Luminosity Large Hadron Collider (HL-LHC) Project at CERN calls for increasing beam brightness and intensity. In such a scenario, critical accelerator devices need to be redesigned and rebuilt. Impedance is among the design drivers, since its thermo-mechanical effects could lead to premature device failures. In this context, the current work reports the results of a multiphysics study to assess the electromagnetic and thermo-mechanical behaviour of the Target Dump Injection Segmented (TDIS). It first discusses the outcomes of the impedance analysis performed to characterise the resistive wall and the high order resonant modes (HOMs) trapped in the TDIS structures. Then, their RF-heating effects and the related temperature distribution are considered. Finally, mechanical stresses induced by thermal gradients are studied in order to give a final validation on the design quality.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK092  
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THPAK093 A Multi-Physics Approach to Simulate the RF Heating 3D Power Map Induced by the Proton Beam in a Beam Intercepting Device HOM, simulation, injection, proton 3452
 
  • L. Teofili, M. Migliorati
    Sapienza University of Rome, Rome, Italy
  • D. Carbajo Perez, F. Giordano, I. Lamas Garcia, G. Mazzacano
    CERN, Geneva, Switzerland
 
  The project High Luminosity Large Hadron Collider (HL- LHC) calls for a streaking beam intensity and brightness in the LHC machine. In such a scenario, beam-environment electromagnetic interactions are a crucial topic: they could lead to uneven power deposition in machine equipment. The resulting irregular temperature distribution would gener- ates local thermal gradients, this would create mechanical stresses which could lead to cracks and premature failure of accelerator devices. This work presents a method to study this phenomenon by means of coupled electro-thermo- mechanical simulations. Further, examples of applications on real HL-LHC devices is also discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK093  
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THPAK103 Pragmatic Method of Deducing a Wake Function for a General 3D Structure wakefield, simulation, vacuum, resonance 3469
 
  • G. Skripka
    CERN, Geneva, Switzerland
  • R. Nagaoka
    SOLEIL, Gif-sur-Yvette, France
 
  A key quantity in simulating collective beam instabilities is the wake potential of a bunch of particles whose charge distribution is continuously evolving in time. However, obtaining such wake potential is only possible if a wake excited by a single particle in the surrounding environment is known. A practical self-consistent approach was developed to obtain an effective wake function from a numerical wake potential computed for a finite length bunch. The wake potential is processed to a numerical impedance which is decomposed into a set of well-known analytical wake functions. The decomposed impedance is then transformed back into time domain and, thus, converted into an effective wake function which is by nature physical and most consistent with the numerical wake potential. Though the method is limited by the initial numerical impedance data and the choice of impedance decomposition, the retrieved wake function can be used in instability simulations with a bunch whose length is comparable to that used in the electromagnetic field solver. We show that the method can be applied to a general 3D structure, which allows finding effective wake functions of realistic vacuum chambers.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK103  
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THPAK115 Numerical Multiparticle Tracking Studies on Coupled-Bunch Instabilities in the Presence of RF Phase Modulation wakefield, cavity, synchrotron, damping 3511
 
  • M. Sommer, B.D. Isbarn, S. Koetter, B. Riemann, T. Weis
    DELTA, Dortmund, Germany
 
  Funding: Work supported by the BMBF under contract no. 05K13PEB.
Since 2008, longitudinal coupled-bunch instabilities are suppressed at DELTA by a modulation of the phase of the accelerating RF field inside the cavity. To achieve a deeper understanding of the interaction of both effects, experimental studies have been made in 2016. These studies show a quadratic dependency of the coupled-bunch mode damping rates on the phase modulation amplitude. Recently, a numerical particle tracking code has been developed to confirm the experimental results. It is based on long range wake field effects produced inside an RF cavity acting on multi particle bunches of arbitrary charge, together with phase focusing by a phase modulated accelerating field. The numerical results confirm the quadratic dependency of damping rates on the phase shift obtained in experimental studies before.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK115  
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THPAK122 Longitudinal Coupled Bunch Instability in JLEIC HOM, cavity, electron, resonance 3530
 
  • R. Li, J. Guo, F. Marhauser, S. Wang
    JLab, Newport News, Virginia, USA
 
  Funding: This work is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The luminosity performance of the JLEIC design is achieved by using a high bunch repetition rate (476MHz) with moderate bunch charges, similar to the strategy employed in modern lepton colliders. Such a bunch configuration will make single bunch instabilities less probable, yet makes the machine more prone to the onset of longitudinal and transverse coupled bunch instabilities. Consequently, this will set higher demands on the bunch-by-bunch feedback systems to mitigate the multi-bunch instabilities. In this paper we present our detailed analysis of the growth rate of the coupled bunch instabilities for beams in both the electron and ion rings in JLEIC at the collision scenario. The implication of the growth rate on the feedback system will be discussed.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK122  
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THPAK123 Updates on Collective Effects Estimations for JLEIC electron, cavity, collider, luminosity 3533
 
  • R. Li, K. E. Deitrick, T.J. Michalski
    JLab, Newport News, Virginia, USA
 
  Funding: This work is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
JLEIC is the high luminosity and high polarization electron-ion collider (EIC) currently under active design at Jefferson Lab. It aims at high luminosity (1033~1034 cm-2s−1) for a wide range of ion species and center-of-mass energies. This luminosity performance relies sensibly on beam stability with high intensity electron and ion beam operation. The impedance budget analysis and the estimations of the single and multibunch instabilities are currently underway. In this paper, we present the update status of estimations for the longitudinal and transverse coherent instabilities, and identify areas or parameter regimes where special attentions for instability mitigations are required.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK123  
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THPAL016 Study of the Performances of a 3D Printed BPM vacuum, HOM, instrumentation, status 3656
 
  • N. Delerue, D. Auguste, J. Bonis, F. Gauthier, A. Gonnin, S. Jenzer, O. Trofimiuk
    LAL, Orsay, France
  • A. Vion
    BV Proto, Sévenans, France
 
  Funding: Work supported by IN2P3 ‘‘3D Metal'' innovation program; Oleh Trofimiuk stay in France is supported by the IDEATE International Associated Laboratory (LIA) between France and Ukraine.
Following previous results which have shown that some components built using additive manufacturing (3D printing) are compatible with ultra high vacuum, we have adapted the design of a stripline BPM to the requirements of additive manufacturing and built it. We report here on the design adaptation and on its mechanical and electrical performances.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL016  
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THPAL018 DQW HOM Coupler Design for the HL-LHC HOM, cavity, simulation, GUI 3663
 
  • J.A. Mitchell
    Lancaster University, Lancaster, United Kingdom
  • G. Burt
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • R. Calaga
    CERN, Geneva, Switzerland
  • S. Verdú-Andrés, B. P. Xiao
    BNL, Upton, Long Island, New York, USA
 
  HOMs in the DQW crab cavity can produce large heat loads and beam instabilities as a result of the high current HL-LHC beams. The DQW crab cavity has on-cavity, coaxial HOM couplers to damp the HOMs whilst providing a stop-band response to the fundamental mode. Manufacturing experience and further simulations give rise to a set of desirable coupler improvements. This paper will assess the performance of the current HOM coupler design, present operational improvements and propose an evolved design for HL-LHC.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL018  
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THPAL057 Development of the Aluminum Beam Duct for the Ultra-Low Emittance Light Source vacuum, experiment, storage-ring, emittance 3775
 
  • G.-Y. Hsiung, J.-R. Chen, C.M. Cheng, S-N. Hsu, H.P. Hsueh, Y.C. Yang
    NSRRC, Hsinchu, Taiwan
  • J.-R. Chen
    National Tsing Hua University, Hsinchu, Taiwan
 
  The future light source with ultra-low emittance, typically < 500 pm rad, requests the beam duct with inner aperture < 20 mm for the electron storage ring. Besides, the cross section of the beam duct must be kept smooth for lowering the impedance. The aluminum extruded beam duct of 10 mm inside and 1 ~ 2 m in length was developed for this purpose. The beam duct was machined in ethanol to obtain a clean surface for a lower thermal outgassing rate. To mitigate the impedance of the flange connection, a special designed diamond-edge gasket and the aluminum flange without knife edge were developed. The inner diameters of both flange and gasket, 10 mm, are the same as that of beam duct. The sealing of the gasket has been proved leak-tight. The ultimate pressure and the thermal outgassing rate of the beam duct has achieved < 2.0·10-10 Torr and < 1.4·10-13 Torr l/(s cm2), respectively after baking. Those results fulfill both the ultrahigh vacuum and lowest impedance are applicable for the next generation ultra-low emittance light source.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL057  
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THPAL059 TEMPERATURE ISSUES OF THE TPS BPMS wakefield, simulation, site, resonance 3781
 
  • Y.T. Huang, C.-C. Chang, C.M. Cheng, P.J. Chou, Y.C. Yang
    NSRRC, Hsinchu, Taiwan
 
  Since the TPS is capable to operate at higher currents, long-term 400mA conditioning runs were conducted. Current-dependent temperature data of BPMs were collected and analysed for both, aluminium and stainless steel BPM chambers. To better understand beam coupling effects in different types of TPS BPMs, electromagnetic and thermal simulation models were established. In this paper, we discuss associated results of such studies.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL059  
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THPAL060 Advanced Modeling of Klystrons by the Tesla-Family of Large-Signal Codes klystron, cavity, experiment, simulation 3785
 
  • I.A. Chernyavskiy, D.K. Abe, B. Levush, A.N. Vlasov
    NRL, Washington, DC, USA
  • T.M. Antonsen
    UMD, College Park, Maryland, USA
  • T.M. Antonsen
    Leidos Corp, Billerica, MA, USA
  • J. Rodgers
    Naval Research Laboratory (NRL), Washington, USA
 
  Funding: US Office of the Naval Research
Klystrons and IOTs are widely used or proposed to be used in accelerators as high-power RF sources. Development and optimization of klystron and IOT designs is aided by the use of different simulation tools, including highly efficient large-signal codes. We present an overview of the advances in the code development and modeling using Naval Research Laboratory (NRL) set of TESLA-family of large-signal codes, suitable for the modeling of single-beam and multiple beam klystrons and IOTs. Original 2D large-signal algorithm of the code TESLA* was developed for the modeling of klystrons based on (relatively) high Q resonators and is applicable to the multiple-beam devices in an approximation of identical beams/beam-tunnels. Parallel extension of TESLA algorithm (code TESLA-MB**) enabled an accurate, quasi-3D modeling of multiple-beam devices with non-identical beams/beam-tunnels. Recently developed more general TESLA-Z algorithm*** is based on the impedance matrix approach and enabled geometry-driven large-signal modeling. Examples of applications of TESLA-family of codes to the modeling of advanced single-beam and multiple-beam klystrons (and IOTs) will be presented.
*A.N. Vlasov, et al,IEEE TPS, v.30(3), 1277-1291, June 2002
**I.A. Chernyavskiy, et al.,IEEE TPS, v.36(3), 670-681, June 2008
***I.A. Chernyavskiy, et al.,IEEE TED, v.64(2), 536-542, Feb 2017
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL060  
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THPAL074 Numerical Studies of Normal Conducting Deflecting Cavity Designs for the ELBE Accelerator cavity, HOM, electron, experiment 3824
 
  • T.G. Hallilingaiah, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • A. Arnold, U. Lehnert, P. Michel
    HZDR, Dresden, Germany
 
  Currently, in the electron linac ELBE there is a single beam line. Therefore, at any given time only single user can use the beam. Moreover, as different user experiments require distinct beam intensity settings, not all the experiments fully utilize the 13 MHz CW beam capability of the facility. To utilize the full beam capacity, multiple beam lines can be established by using an array of transverse deflecting structures. For that, an RF cavity was the design choice due to its inherent advantages with respect to repeatability of the kick voltage amplitude and phase, and the possibility of CW operation in the MHz range. Potential design candidates are the CEBAF RF separator, the three proposed crab cavities for the HL-LHC upgrade project, and a novel NC deflecting cavity design. In this comparative study, the figures of merit of the cavities are computed from electromagnetic field simulations for a transverse voltage of 300 kV. This comparative study supported our selection of the deflecting cavity design for ELBE.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL074  
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THPAL080 Parallel-Feed SRF Accelerator Structures cavity, SRF, coupling, simulation 3835
 
  • P.B. Welander, Z. Li, M.H. Nasr, S.G. Tantawi
    SLAC, Menlo Park, California, USA
 
  Funding: This work is supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
Development of SRF accelerator technology that enables both higher gradient and higher efficiency is crucial for future machines. While much of the recent R&D focus has been on materials and surface science, our aim is to optimize the cavity geometry to maximize performance with current materials. The recent demonstration of a highly efficient parallel-feed NCRF structure at SLAC has served as a proof-of-concept. Applied to SRF, such a structure could dramatically reduce power consumption while boosting the achievable gradient. Instead of coupled elliptical cells, our structure employs isolated reentrant cells. To feed RF power to the cavities, each cell is directly coupled to an integrated manifold. The structure is made in two parts, split along the beam axis, which are then joined. Such a structure has been fabricated from bulk Cu and tested at SLAC - designed for X-band, it operates at a record gradient of 150 MV/m. Adapting to SRF at 1.3 GHz and fabricating from Nb, such a cavity could achieve more than 50% lower RF loss and 40% higher gradient compared to the TESLA cavity. We will describe our simulations and propose an experimental roadmap for demonstrating this technology.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL080  
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THPAL101 Longitudinal Effects of Trapped Homs in Shanghai Coherent Light Facility cavity, HOM, linac, FEL 3872
 
  • J.J. Guo, Q. Gu, H.T. Hou, J.H. Tan, M. Zhang
    SINAP, Shanghai, People's Republic of China
 
  Funding: Shanghai Institute of Applied Physics, Chinese Academy of Sciences
Shanghai Coherent Light Facility (SCLF), a superconducting accelerated structure-baesd FEL device, is now under development at Shanghai Institute of Applied Physics, Chinese Academy of Sciences. We investigate effects of cryogenic losses caused by trapped longitudinal high order modes (HOM). Results of calculations are presented for losses caused by HOMs excitation in the acceleration RF system of the continues-wave (CW) linac of SCLF.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL101  
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THPAL109 The New 118 MHz Cavity for RF Development Activities of the RF for Accelerator Laboratory at SLRI cavity, simulation, HOM, coupling 3895
 
  • N. Juntong, K. Kittimanapun, P. Sunwong
    SLRI, Nakhon Ratchasima, Thailand
  • A. Sutchada
    Walailak University, Nakhon Si Thammarat, Thailand
 
  The RF for accelerator laboratory is established at SLRI to perform RF related development activities of the current light source and the future synchrotron light facility in Thailand. One of activities is to build an in-house RF cavity. It will be used for testing of RF amplifier unit and the developed LLRF system. The cavity is a nose-cone pill-box cavity operating at 118 MHz and aiming at 100 kV gap voltage. Details of designing in particular the inner surface profile, the RF properties, the higher order modes properties, the RF power coupler, and the tuning mechanism will be presented with the manufacturing timeline.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL109  
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THPMF013 The Stripline Kicker Prototype for the CLIC Damping Rings at ALBA: Installation, Commissioning and Beam Characterisation kicker, extraction, storage-ring, synchrotron 4062
 
  • M. Pont, N. Ayala, M. Carlà, T.F.G. Günzel, U. Iriso, Z. Martí, R. Monge, A. Olmos, F. Pérez, M. Quispe
    ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
  • M.J. Barnes, C. Belver-Aguilar, Y. Papaphilippou
    CERN, Geneva, Switzerland
 
  The extraction system for the CLIC Damping Rings has very tight specifications. Therefore a full characterisation of the behaviour of the stripline kicker under conditions as close as possible to the expected working conditions will be very valuable. To that end the CLIC stripline has been installed in the ALBA Synchrotron Light Source and has been characterised with beam. Prior to its installation, the effect of the stripline kicker on the machine impedance has been assessed. The installation has required the design of an absorber to screen the stripline from synchrotron radiation and additional BPMs have been installed for a better kick angle determination. The commissioning of the stripline with beam has been performed following closely beam parameters, pressure and temperature. The studies with beam include the determination of the longitudinal and transverse impedance of the kicker*, the field homogeneity when excited with a dc field and the field ripple when pulsed. This contribution reports on the first experience with the stripline kicker for the CLIC DR in the ALBA storage ring and presents the results of the initial beam characterisation.
* M. Carla et al., "Beam based impedance measurements of the CLIC stripline at ALBA", Proc. of IPAC'2017.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF013  
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THPMK018 Design of a rotationally symmetric S-band photocathode RF gun gun, cathode, emittance, coupling 4336
 
  • Zh. X. Tang
    USTC, Hefei, Anhui, People's Republic of China
  • Z.G. He, W.W. Li, Y.J. Pei, L. Wang
    USTC/NSRL, Hefei, Anhui, People's Republic of China
 
  The photocathode RF gun is one of the most critical components for high quality electron beam sources. The asymmetric multi-pole field contributes to the transverse emittance growth and degrades the beam quality. In order to overcome the problem, we propose a novel rotationally symmetric 1.6 cell RF gun to construct the symmetric field in this paper. The concrete proposal is that a coaxial cell with a symmetrical distribution of four grooves is concatenated to the first 0.6 cell at the photocathode end to form a new resonant cell (NRC) to mantain the symmetric multi-pole field in 1.6 cell. Our simulations indicate that 3D multi-pole fields of NRC are with the perfect symmetry. After that, the profile of the RF gun is optimized to improve the shunt impedance and mode separation and make the surface peak electric field at the photocathode end. Our simulations demonstrate promising outlook of using coaxial cell for photocathode RF guns with various applications.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK018  
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THPMK048 The Design and Construction of a Novel Dual-Mode Dual-Frequency Linac Design operation, cavity, resonance, acceleration 4391
 
  • M.H. Nasr, S.G. Tantawi
    SLAC, Menlo Park, California, USA
 
  One promising approach in boosting accelerators efficiency is dual-mode simultaneous operation. In our work, the topic of dual-mode acceleration is studied from a wider perspective with new approaches and tools. We present a new type of accelerator structures that operates simultaneously with two modes and two frequencies. The frequencies are not constrained to be harmonically related, but rather have a common sub-harmonic. These designs will utilize a newly developed parallel-feeding network that feeds each individual accelerating cell independently using a distributed feeding network. As a result, the design problem converges to a single-cell design with identical cells. The cells are designed for maximum efficiency using new geometrical optimization that utilizes nonuniform rational B-spline (NURBS) with a series of control points. We will present a study on the topic for S-band simultaneous operation with C-band or X-band.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK048  
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THPMK049 New Geometrical-Optimization Approach using Splines for Enhanced Accelerator Cavities' Performance controls, cavity, simulation, accelerating-gradient 4395
 
  • M.H. Nasr, S.G. Tantawi
    SLAC, Menlo Park, California, USA
 
  Over the past decades accelerator scientists made a huge effort in advancing the technology of particle accelerators, which lead to state-of-the-art fabrication techniques as well as simulation tools. Combining these advancements with the large boosting in computing speed provides large flexibility and motivation to investigate new accelerator geometries. In this paper, we describe a new optimization approach for the geometry of accelerating cells. This approach uses a set of control points with variable positions to control a non-uniform rational B-spline (NURBS), which describes the cavity shape. The positions of the control points are then optimized using differential-evolution optimization to maximize/minimize a defined optimization function, which is defined by the user and depends on the cavity parameters such as the shunt impedance, wall losses, peak surface fields…etc. This optimization approach leads to accelerator geometries with enhanced performance and very smooth surface fields.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK049  
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THPMK095 Design of an RF Modulated Thermionic Electron Source at TRIUMF GUI, electron, cathode, gun 4524
 
  • K. Fong, D.W. Storey
    TRIUMF, Vancouver, Canada
 
  The electron source in the TRIUMF ARIEL project is a gridded dispenser cathode. The cathode is biased at -300kV, and the grid requires a RF control signal of up to 150V at 650 MHz. The required RF power is approximately 20 W and is provided by an RF amplifier located outside the gun vessel. This RF power is coupled into the gun circuit through a ceramic transmission line. The design of this ceramic transmission line, as well as the impedance transformation circuit which provides both the impedance matching and the dc powers to the gun assembly are described.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK095  
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THPML006 Using Drive Rods in Inductions Cells to Reduce the Beam Break Up Instability simulation, induction, wakefield, cavity 4658
 
  • N. Pogue, T.L. Houck, B.R. Poole
    LLNL, Livermore, California, USA
 
  The Beam Breakup Instability is a critical effect to reduce in high current induction accelerators. The RF modes generated inside the induction cells can deflect or degrade subsequent beam traversing the cell. Significant effort has been invested in minimizing the effect over several decades. One mechanism that is known to reduce the transverse impedance, the main observable experimentally which directly relates to the BBU amplitude, is to introduce ferrites to absorb the fields. Another, less investigated mechanism, is to disturb the modes symmetry by inserting the drive rods at the proper locations in the cell. This paper will show that the drive rods can dramatically reduce the transverse impedance, and will show that simulations are maturing towards predicting this effect. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML006  
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THPML055 Scaled Studies on Radio Frequency Sources for Megawatt-Class Ionospheric Heaters electron, gun, cathode, experiment 4763
 
  • B.L. Beaudoin, T.M. Antonsen, J.A. Karakkad, A.H. Narayan, G.S. Nusinovich, K.J. Ruisard
    UMD, College Park, Maryland, USA
  • R. Fischer
    Naval Research Laboratory (NRL), Washington, USA
  • S.H. Gold, A. Ting
    NRL, Washington,, USA
 
  Funding: Funding for this project and travel is provided by the Air Force Office of Scientific Research under grant FA95501410019.
The ionosphere plays a prominent role in the performance of critical civilian and military communication systems. The key instrument in Ionospheric Modification (IM) research is a powerful, ground-based, High Frequency (HF) source of electromagnetic waves known as a heater. With a mobile heater, investigators would be able to conduct IM research at different latitudes without building a costly permanent installation. A new highly efficient Megawatt class of Radio Frequency sources is required to reduce the overall power demands on a fully deployable system. Such a source has been described previously*. Results of a scaled experiment, using the electron beam produced by a gridded gun to drive an external lumped element circuit for high efficiency radio frequency generation is presented. The IOT gun produces an electron beam bunched at the driving frequency that is then collected by an external circuit for impedance matching to the load. Results showed that effects such as the internal resistance of the inductor and deflection of beam electrons by the induced RF voltages on the beam collector are important considerations to be included in the design of a practical device.
* B.L. Beaudoin, G.S. Nusinovich, G. Milikh, A. Ting, S. Gold, J.A. Karakkad, A.H. Narayan, D.B. Matthew, D.K. Papadopoulos, T.M. Antonsen Jr., Journal of Elec. Waves and Appl.,31,17,pp.1786, 2017.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML055  
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THPML096 A Non-Invasive Magnetic Momentum Monitor Using a TE011 Cavity cavity, electron, GUI, coupling 4889
 
  • J. Guo, J. Henry, M. Poelker, R.A. Rimmer, R. Suleiman, H. Wang
    JLab, Newport News, Virginia, USA
 
  Funding: Authored by Jefferson Science Associates, LLC with Laboratory Directed Research and Development funding, under U.S. DOE Contract No. DE-AC05-06OR23177.
The Jefferson Lab Electron-Ion Collider (JLEIC) design relies on cooling of the ion beam with bunched electron beam. The bunched beam cooler complex consists of a high current magnetized electron source, an energy recovery linac, a circulating ring, and a pair of long solenoids where the cooling takes place. A non-invasive real time monitoring system is highly desired to quantify electron beam magnetization. The authors propose to use a passive copper RF cavity in TE011 mode as such a monitor. In this paper, we will show the mechanism and scaling law of this device, as well as the design and testing results of the prototype cavity.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML096  
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THPML112 Preliminary Design and Calculation of Button BPM for the HALS Storage Ring storage-ring, vacuum, HOM, electronics 4929
 
  • F.F. Wu, F.L. Gao, L.T. Huang, X.Y. Liu, P. Lu, B.G. Sun, J.H. Wei, Y.L. Yang, T.Y. Zhou
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • L. Lin
    Huizhou University, Huizhou, People's Republic of China
 
  Funding: Supported by the National Science Foundation of China (Grant No.11705203, 11575181,11605202) and the National Key Research and Development Program of China(No. 2016YFA0402000)
Button BPM is being designed for the HALS storage ring, which is a diffraction-limited storage ring (DLSR) located at the NSRL in Hefei city. Since beam size is very small, the required resolution of 50 nm for beam position measurement need to be obtained. The parameters of the HALS Button BPM are initially determined. According to theoretical formulas, electrode induced signal is calculated and the relationship between electrode induced signal and beam current is obtained. Signal to noise ratio(SNR)of the HALS Button BPM is calculated with different beam current when the required resolution is 50 nm. The results show that the SNR is well when beam current is very low. In addition, the effects of BPM RF frequency and button electrode radius on SNR are analyzed.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML112  
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THPML125 Efficiency Analysis of High Average Power Linacs for Environmental and Industrial Applications linac, beam-loading, 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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