IPAC2019 - List of Keywords (impedance)

Paper	Title	Other Keywords	Page
MOPGW001	Design Review of Bellows RF-Shielding Types and New Concepts for Sirius	shielding, storage-ring, wakefield, HOM	53
	H.O.C. Duarte, P.P.S. Freitas, A.R.D. Rodrigues, R.M. Seraphim, T.M. da Rocha LNLS, Campinas, Brazil
	Large amounts of bellows in an accelerator justify the importance of simplifying the machining and assembling processes of their RF shield. Such quantity also makes this component one of the main contributors for a machine impedance budget. On the other hand, low impedance designs tend to complicate the mechanical aspects. Applied to Sirius round vacuum chamber of 24 mm inner diameter, the omega-strip and comb-type bellows concepts are compared with new proposed designs. In such comparison, the aforementioned aspects, wakefield losses and prototyping experiences are presented in this work.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW001
About •	paper received ※ 16 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW003	Collective Instability Studies for Sirius	simulation, storage-ring, radiation, coupling	61
	F.H. de Sá LNLS, Campinas, Brazil
	In this work we will present the estimates of single and multi-bunch instability thresholds and current-dependent effects, such as tune-shifts and potential-well distortion for the Sirius storage ring. The results were obtained by tracking simulations and semi-analytic methods using the updated and detailed impedance budget of the machine, which includes contributions from all the in-vacuum components and the coherent synchrotron radiation (CSR) impedance.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW003
About •	paper received ※ 15 May 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019
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MOPGW035	Coupling Impedance of the Collimator Without RF-Shields at the RCS in J-PARC	simulation, synchrotron, collimation, proton	163
	Y. Shobuda, J. Kamiya, K. Moriya, K. Okabe JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
	All holes on the chamber walls of synchrotrons should be filled with the radiofrequency (RF)-shields to suppress coupling impedances that excite beam instabilities. In a synchrotron, titanium nitride (TiN)-coated RF-shields are installed with collimators. If the holes, through which the collimator jaw enters and exits the chamber, are filled with such RF-shields, the shields may break down as the dynamic coefficient of TiN increases in vacuum. At the Rapid Cycling Synchrotron (RCS), the RF-shields are eliminated from the collimator after demonstrating that the effect due to the RF-shields is negligible on the impedance at low frequencies.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW035
About •	paper received ※ 28 April 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019
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MOPGW036	Studies on Coherent Multi-Bunch Tune Shifts with Different Bunch Spacing at the J-PARC Main Ring	space-charge, proton, operation, injection	167
	A. Kobayashi, S. Igarashi, Y. Sato, T. Shimogawa, Y. Sugiyama, T. Toyama, M. Yoshii KEK, Tokai, Ibaraki, Japan
	At a high-power proton synchrotron, betatron tune shifts induced by space charge effects cause beam loss which limits the beam intensity. To achieve further high beam intensity at the main ring of the Japan Proton Accelerator Research Complex, precise control of the tune shift is indispensable. When carrying out multi-bunch measurements, we observed that the dependence of the tune shift intensity on the number of bunches follow opposite slope trends for the horizontal and vertical directions. The influence of the bunch spacing was also observed. We report on a simplified tune shift model reconstruction for understanding the origin of these phenomena and present a correction of the tune shifts for reducing beam loss up to 30 %.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW036
About •	paper received ※ 01 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW037	Dynamic Variation of Chromaticity for Beam Instability Mitigation in the 3-GeV RCS of J-PARC	simulation, emittance, extraction, injection	171
	P.K. Saha, H. Harada, H. Hotchi, Y. Shobuda, T. Takayanagi, F. Tamura, Y. Watanabe JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
	We have studied many other dynamic approaches from that reported in the IPAC 2018 for transverse beam instability mitigation in the presence of strong space charge in the 3-GeV RCS of J-PARC. One of such a method is the introduction of an excess of chromaticity from that of natural chromaticity by reversing the sextupole magnetic fields from the middle of the acceleration cycle. The benifits of this method are twofold. It allows to utilize sextupole for chromaticty correction at lower energy and also mitigate the beam instability at higher energy because of introducing higher chromaticity. We first carried out numerical simulations by using ORBIT code, experimentally verified and then applied for the machine operation. The detail of simulation and measurements results are presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW037
About •	paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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MOPGW039	Investigation of Longitudinal Beam Dynamics With Harmonic Cavities by Using the Code Mbtrack	cavity, operation, synchrotron, beam-loading	178
	N. Yamamoto KEK, Ibaraki, Japan A. Gamelin, R. Nagaoka SOLEIL, Gif-sur-Yvette, France
	In diffraction-limited light sources, the study of collective effects is essential. With harmonic cavities (HCs), the ’flat potential condition’ can be achieved, lengthening the bunch by a factor of ~5. However, the effective rf voltage seen by the beam becomes sensitive to both positions and distributions of all bunches, as the beam-induced voltage of both HCs and fundamental cavities (FCs) contribute. In addition, when there are empty buckets, the transient beam loading induces considerable variations of the rf voltage impacting the beam performance. Here the use of analytical approaches is difficult. Then we introduced the new functions to treat the high-Q resonators driven by either or both of the beams and external generators to the code mbtrack. Using these features, various operating conditions with arbitrary fill patterns can be studied; coupled bunch instability induced by HOMs of the cavity, Robinson instabilities and general beam dynamics with HCs. The growth rates of the instabilities described above are compared with analytical results. The ring performance with HCs in several fill patterns shall be also reported. N.Yamamoto, et al., PRAB, 21, 012001 (2018). **G. Skripka, et al., NIM A806, 221 (2016).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW039
About •	paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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MOPGW052	The Study of Single-Bunch Instabilities in the Ramping Process in the HEPS Booster	booster, simulation, lattice, injection	206
	H.S. Xu, Y.M. Peng, N. Wang IHEP, Beijing, People’s Republic of China
	The booster of High Energy Photon Source (HEPS) is proposed to ramp the beam energy from 500 MeV to 6 GeV, and to deliver the required charge to the storage ring. However, the transverse single-bunch instability may limit the reachable bunch charge in the booster. The study of the transverse single-bunch instability has been carried out for the HEPS booster at both 500 MeV and 6 GeV to double check whether the required single-bunch charge can be achieved. Furthermore, the energy ramping process was recently included in the study. We concentrate in the analyses of the simulation results with the consideration of energy ramping process in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW052
About •	paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW058	Towards a Sextupole-Free Electron Storage Ring	electron, vacuum, storage-ring, feedback	217
	T.-Y. Lee, T. Ha PAL, Pohang, Kyungbuk, Republic of Korea
	This paper studies if it is possible to build an electron storage ring with no or a small number of sextupole mag-nets. If it is possible, the electron storage ring will be great-ly simplified. For the purpose, two methods are presented in the paper to handle head-tail instability: One is to use dielectric vacuum chamber made of such materials as ceramic or glass to reduce broadband impedance signifi-cantly. Then head-tail instability would be extremely weak. The other method is to install a bunch-by-bunch feedback system to suppress the already weak head-tail instability due to the dielectric vacuum chamber.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW058
About •	paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW064	On Wakefield in Dielectric Waveguide with Shallow Corrugation of Metallic Wall	GUI, radiation, ECR, wakefield	237
	A.V. Tyukhtin, E.R. Akhmatova, T.Yu. Alekhina, S.N. Galyamin, V.V. Vorobev Saint Petersburg State University, Saint Petersburg, Russia
	Funding: This work was supported by the Russian Science Foundation (Grant # 18-72-10137). Bunch radiation in periodical waveguides was mainly analyzed for situations when wavelengths are comparable to the structure period (Smith-Purcell emission). However, it is also of interest to study the "long-wave radiation" with wavelengths which are much larger than the structure period,. In such situation, the exact boundary conditions on the complicated periodic surface can be replaced with the equivalent boundary conditions (EBC) which must be fulfilled on the smooth surface. Earlier we considered with this approach radiation of the bunch moving along the axis of circular vacuum corrugated waveguide. Comparison of analytical results with COMSOL simulations showed high accuracy of the EBC method. Here we analyze an analogous problem for the waveguide with corrugated wall and dielectric filling under condition that Cherenkov effect takes place in the dielectric. Due to this fact the radiation differs radically from that in the vacuum waveguide. At the same time, the radiation has essential differences from the one in the usual dielectric waveguide. The radiation properties in the waveguide under consideration and its differences from the radiation in the waveguide with smooth wall are analyzed. G. Stupakov, K. Bane, Phys. Rev. ST-AB, 15 (2012) 124401. ** A.V. Tyukhtin et al, J. of Instrumentation, 13 (2018) C04009.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW064
About •	paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW066	Local Impedance Measurements Using the Orbit Bump Method at ALBA	storage-ring, betatron, simulation, vacuum	240
	Z. Martí, G. Benedetti, T.F.G. Günzel, U. Iriso ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
	The orbit bump technique has been used at the ALBA Storage Ring to characterize with good precision the impedance of single machine elements, like the in-vacuum undulators or the CLIC stripline kicker. The results are compared with theoretical studies, as well as impedance measurements done at ALBA using other methods like the turn by turn betatron phase or from the analysis of the detuning slopes of the Transverse Mode Coupling Instability.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW066
About •	paper received ※ 14 May 2019 paper accepted ※ 17 May 2019 issue date ※ 21 June 2019
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MOPGW068	Crosstalk of Beam-Beam Effect and Longitudinal Impedance at CEPC	simulation, luminosity, collider, factory	247
	Y. Zhang, N. Wang, C.H. Yu IHEP, Beijing, People’s Republic of China C.T. Lin University of Chinese Academy of Sciences, Beijing, People’s Republic of China
	Funding: Project 11775238 supported by NSFC In conventional e⁺e⁻ storage ring colliders, we only use lengthend bunch length in beam-beam simulation instead of considering impedance directly. It is no problem since the longitudinal dynamics is not sensitive to beam-beam interaction. But it is different since the bunch will also be lengthend during beam-beam interaction by beamstrahlung effect. It is very natural and more self-consistent to consider the longitudinal impedance in the beam-beam simulation. The simulation shows that the working point region of stable collision is slightly shifted by the longitudinal impedance. It is found that the vertical coherent oscillation may decreases the beam-beam limit with impedance at some working point.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW068
About •	paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW074	New Spiral Beam Screen Design for the FCC-hh Injection Kicker Magnet	kicker, injection, coupling, vacuum	270
	A. Chmielinska, M.J. Barnes CERN, Geneva, Switzerland
	The injection kicker system for the Future Circular Collider (FCC-hh) must satisfy demanding requirements. To achieve low pulse ripple and fast field rise and fall times, the injection system will use ferrite loaded transmission line type magnets. The beam coupling impedance of the kicker magnets is crucial, as this can be a dominant contribution to beam instabilities. In addition, interaction of the high intensity beam with the real part of the longitudinal beam coupling impedance can result in high power deposition in the ferrite yoke. This gives a significant risk that the ferrite yoke will exceed its Curie temperature: hence, a suitable beam screen will be a critical feature. In this paper, we present a novel concept - a spiral beam screen. The fundamental advantage of the new design is a significant reduction of the maximum voltage induced on the screen conductors, thus decreased probability of electrical breakdown. In addition, the longitudinal beam coupling impedance is optimized to minimize power deposition in the magnet.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW074
About •	paper received ※ 26 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW076	Verification by RF Measurements of New HOM Mitigation Scheme Developed for Future SPS 33-Cell Accelerating Structures	HOM, damping, simulation, coupling	274
	P. Kramer, A. Farricker, C. Vollinger CERN, Geneva, Switzerland
	Longitudinal higher-order modes (HOMs) at a frequency of around 630 MHz in the 200 MHz travelling wave RF structures currently limit the beam intensities in the CERN SPS to less than that required by the High Luminosity (HL-) LHC. In the framework of the LHC Injectors Upgrade (LIU) project, the performance of the already existing HOM damping scheme for these standing wave modes must be improved. This involves improving the existing HOM-couplers as well as the possible use of a new mitigation technique via the insertion of resonant posts in some cells of the multi-cell structures. The development of the new damping scheme has been performed using theoretical analysis of the cavity-coupler interaction in conjunction with full-wave electromagnetic (EM) field simulations. This contribution will show the verification of the improved HOM damping performance by measurements on a single section with 11 cells and on the future 33-cell structures. The parasitic impact of the damping scheme on the travelling wave fundamental passband (FPB) will also be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW076
About •	paper received ※ 11 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW077	Impedance Reduction in the CERN SPS Through Element Layout Optimisation	coupling, extraction, cavity, quadrupole	277
	A. Farricker, C. Vollinger CERN, Geneva, Switzerland
	The CERN accelerator complex is currently in its long shutdown while the LHC Injector Upgrade is being carried out. The upgrade of the SPS includes but is not limited to: the relocation of the beam dumping system, upgrade of the RF system, replacement of the electrostatic septa and impedance reduction. These major upgrades present an opportunity to perform additional impedance reduction in areas not normally modified due to the large amount of work being performed across the accelerator complex. In this paper, we look at the impedance minimization in the sections near the large aperture quadrupoles of the extraction regions in the CERN SPS. By optimizing the locations of existing equipment and the introduction of a new, more impedance optimised type of bellows, significant reductions in the beam-coupling impedance can be achieved.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW077
About •	paper received ※ 08 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW083	Longitudinal Coupled-Bunch Instability Evaluation for FCC-hh	emittance, cavity, HOM, synchrotron	297
	I. Karpov, E.N. Shaposhnikova CERN, Meyrin, Switzerland
	High-order modes (HOM) of the accelerating rf structures and other machine elements, if not sufficiently damped, can drive longitudinal coupled-bunch instabilities (CBI). Their thresholds can be accurately obtained from macro-particle simulations using the detailed impedance model containing many different contributions. This method, however, is very difficult to apply for synchrotrons with a large number of bunches, as it is the case for the Future Circular hadron-hadron Collider (FCC-hh) with up to 10400 circulating bunches per beam. In this paper the semi-analytical approach is used for calculations of the instability thresholds during the acceleration cycle of the FCC-hh. As the result, we define requirements for the HOM damping that would be sufficient to prevent development of longitudinal CBI in the presence of weak synchrotron radiation damping.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW083
About •	paper received ※ 13 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW084	Beam Loading Compensation for the Future Circular Hadron-Hadron Collider (FCC-hh)	cavity, beam-loading, hadron, collider	301
	I. Karpov, P. Baudrenghien CERN, Meyrin, Switzerland
	The power consumption of the rf system can be minimised by optimising the cavity detuning and the loaded quality factor. In high-current accelerators, the presence of gaps in the filling results in a modulation of the cavity voltage along the ring (transient beam loading) and as a consequence a spread in the bunch parameters. In addition longitudinal coupled-bunch instabilities can appear, caused by the cavity impedance at the fundamental. Both issues can be mitigated by using an rf feedback around the amplifier and cavity, a technique used in many high intensity machines including the Large Hadron Collider (LHC). Compared to the LHC machine, the energy increase and the radiation loss for the Future Circular hadron-hadron Collider (FCC-hh) will be larger, resulting in a synchronous phase deviating significantly from 180 degrees. The solutions adopted for the LHC must therefore be revisited. This paper evaluates several beam loading compensation schemes for this machine.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW084
About •	paper received ※ 13 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW087	GALACTIC and GALACLIC: Two Vlasov Solvers for the Transverse and Longitudinal Planes	synchrotron, resonance, simulation, coupling	312
	E. Métral CERN, Geneva, Switzerland
	GALACTIC and GALACLIC, two Vlasov solvers for the study, in the transverse and longitudinal plane respectively, of single-bunch coherent oscillation modes, were recently developed starting from the Vlasov equation and using a decomposition on the low-intensity eigenvectors, as proposed by Laclare and Garnier. The first Vlasov solver was used for instance to shed light on the destabilising effect of resistive transverse dampers and the second helped understanding the details of the mode-coupling behind some longitudinal microwave instabilities. Both theories are reviewed in detail, highlighting in particular the similarities and peculiarities of the two approaches.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW087
About •	paper received ※ 23 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPGW088	A Two-Mode Model to Study the Effect of Space Charge on TMCI in the "Long-Bunch" Regime	coupling, space-charge, optics, simulation	316
	E. Métral CERN, Geneva, Switzerland
	Using a two-mode approach for the Transverse Mode-Coupling Instability (TMCI) in the ’short-bunch’ regime (where the mode-coupling takes place between the modes 0 and -1, such as in the CERN LHC), both a reactive damper (ReaD) and Space Charge (SC) are expected to be beneficial: the ReaD would shift the mode 0 up while SC would shift the mode -1 down, but in both cases the coupling (and related instability) would occur at higher intensities. However, the situation is more involved in the ’long-bunch’ regime (where the mode-coupling takes place between higher-order modes, such as in the CERN SPS). As the ReaD modifies only the (main) mode 0 and not the others, it is expected to have no effect for the main mode-coupling. As concerns SC, it modifies all the modes except the mode 0, and the result has been a subject of discussion for two decades. A two-mode approach is discussed in detail in this contribution for the case of a single bunch interacting with a broad-band resonator impedance in the ’long-bunch’ regime. This model reveals in particular that in the presence of space charge, the intensity threshold can only be similar to or lower than that in the absence of space charge.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW088
About •	paper received ※ 23 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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MOPGW089	Longitudinal Mode-Coupling Instability: GALACLIC Vlasov Solver vs. Macroparticle Tracking Simulations	simulation, coupling, synchrotron, proton	320
	E. Métral CERN, Geneva, Switzerland M. Migliorati Rome University La Sapienza, Roma, Italy M. Migliorati INFN-Roma1, Rome, Italy
	Following the same approach as for the recently developed GALACTIC Vlasov solver in the transverse plane and taking into account the potential-well distortion, a new Vlasov solver, called GALACLIC, was developed for the longitudinal plane. In parallel, a new mode analysis was implemented for the post-processing of the results obtained through macroparticle tracking simulations. The results of the several benchmarks performed between the two methods are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW089
About •	paper received ※ 23 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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MOPGW091	Capture and Flat-Bottom Losses in the CERN SPS	beam-loading, injection, emittance, feedback	327
	M. Schwarz, A. Lasheen, G. Papotti, J. Repond, E.N. Shaposhnikova, H. Timko CERN, Meyrin, Switzerland
	Particle losses on the flat bottom of the SPS, the last accelerator in the injector chain of the LHC at CERN, are a strong limitation for reaching the high intensities required by the high luminosity upgrade of the LHC. Two contributions to these losses are investigated in this paper. The first losses occur during the PS-to-SPS bunch-to-bucket transfer, since the bunch rotation in the PS creates halo particles and the bunch does not completely fit into the SPS RF-bucket. The effect of longitudinal shaving in the PS on the beam transmission was recently tested. At high intensities, further capture losses are caused by beam loading in the traveling wave RF system of the SPS, which is partially compensated by the LLRF system, in particular by one-turn delay feedback. While the feedforward system reduces the capture losses, it also increases the losses along the flat bottom due to the RF noise.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW091
About •	paper received ※ 09 May 2019 paper accepted ※ 19 May 2019 issue date ※ 21 June 2019
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MOPGW099	Vlasov-Fokker-Planck Simulations of Passive Higher-Harmonic Cavity Effects in ALS-U	cavity, simulation, synchrotron, resonance	357
	G. Bassi BNL, Upton, Long Island, New York, USA
	Funding: Work supported by DOE under contract DE-SC0012704 We discuss numerical simulations of the Vlasov-Fokker-Planck equation to model passive higher-harmonic cavity (HHC) effects with parameters of the Advanced Light Source Upgrade (ALS-U. The numerical results, obtained with the SPACE code, are compared with a modal analysis of the coupled-bunch instability theory.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW099
About •	paper received ※ 18 May 2019 paper accepted ※ 24 May 2019 issue date ※ 21 June 2019
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MOPGW122	Beam-based Measurement of Broadband Longitudinal Impedance at NSLS-II	vacuum, simulation, diagnostics, storage-ring	400
	V.V. Smaluk, B. Bacha, G. Bassi, A. Blednykh BNL, Upton, Long Island, New York, USA
	Funding: Department of Energy Contract No. DE-SC0012704 Interaction of a particle beam with the vacuum chamber impedance is one of the main effects limiting the beam intensity in accelerators. Minimization of the impedance is an essential part of the vacuum chamber design for any new accelerator project. The impedance can be estimated experimentally by measuring beam dynamics effects caused by the beam-impedance interaction. Experience obtained at many accelerator facilities shows the beam-based measurements are often different from the pre-computed impedance budgets, the discrepancy of a factor of two or even more is not unusual. The measurements of broadband longitudinal impedance carried out at NSLS-II are discussed in comparison with the numerically simulated impedance budget.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW122
About •	paper received ※ 15 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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MOPMP037	Updated High-Energy LHC Design	injection, emittance, proton, damping	524
	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, J. Keintzel, R. Kersevan, V. Mertens, J. Molson, 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, A. Abramov, E. Cruz Alaniz, H. Pikhartova, 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
	Funding: This work was supported in part by the European Commission under the HORIZON 2020 project ARIES no.730871, and by the Swiss Accelerator Research and Technology collaboration CHART. We present updated design parameters for a future High-Energy LHC. A more realistic turnaround time has led to a revision of the target peak luminosity, as well as a choice of a larger IP beta function, and longer physics fills. Pushed parameters of the Nb₃Sn superconducting cable together with a modified layout of the 16 T dipole magnets resulted in revised field errors, updated dynamic-aperture simulations, and an associated re-evaluation of injector options. Collimators in the dispersion suppressors help achieve satisfactory cleaning performance. Longitudinal beam parameters ensure beam stability throughout the cycle. Intrabeam scattering rates and Touschek lifetime appear benign.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPMP037
About •	paper received ※ 10 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPRB006	HOM Damping Options for the Z-Pole Operating Scenario of FCC-ee	HOM, cavity, damping, dipole	590
	S. Gorgi Zadeh Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany R. Calaga CERN, Meyrin, Switzerland T. Flisgen FBH, Berlin, Germany U. van Rienen University of Rostock, Rostock, Germany
	The Z-pole option of FCC-ee is an Ampere class machine with a beam current of 1.39 A. Due to high HOM power and strong HOM damping requirements, the present baseline of FCC-ee considers a single cell cavity at 400 MHz. In this paper, different HOM damping schemes are compared for the Z-pole operating scenario with the aim of lowering the parasitic longitudinal and transverse impedance. The HOM power for each damping scheme is also calculated.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB006
About •	paper received ※ 15 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPRB018	Conceptual Design of Negative-Muon Decelerator for Material Science	cavity, induction, experiment, power-supply	610
	C. Ohmori, M. Otani, K. Shimomura KEK, Tokai, Ibaraki, Japan T. Takayanagi JAEA/J-PARC, Tokai-mura, Japan
	In 2018, a Negative-Muon Spin Rotation and Relaxation technique was developed in J-PARC Material and Life Science Facility. It is a novel scheme to investigate the motion of hydrogens in the chemicals and materials. To study small samples, the surface of materials and thin foils, a low energy negative muon beam is required. To decelerate intense 300-keV muons to 15-keV, we propose a system which consists of pulse generators and multi-gap induction decelerators. In this design, an inductive adder scheme is considered to use for the high voltage pulse source. High impedance magnetic alloy ring cores will be loaded in the decelerator cells. The high impedance cores which have much larger size than those for public use were developed for J-PARC RF systems and used for many applications including CERN booster RF, anti-proton deceleration and medical accelerator. In this paper, we present a conceptual design of muon deceleration system.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB018
About •	paper received ※ 13 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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MOPRB033	Preliminary Research of HOM for 100MHz Superconducting Cavity in the Pre-Research Project of HALS	HOM, cavity, damping, simulation	649
	Y.G. Tang, L. Wang, C.-F. Wu USTC/NSRL, Hefei, Anhui, People’s Republic of China
	A 100MHz QWR superconducting cavity is researched in the pre-research project of Hefei Advanced Light Source (HALS). Higher order modes (HOM) damping is a big challenge for synchrotron radiation light source. In this paper, we first apply the novel choke mode structure to the 100MHz QWR (quarter wave resonator) cavity in order to damp the HOM. We identify the main harmful higher order modes. The HOMs in the QWR cavity are suppressed by optimizing the choke dimensions. The broadband HOM impedance spectrum of the cavity was also evaluated by calculating the beam induced wake potential in time domain. The results show that choke mode structure has a good HOM damping effect on the QWR cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB033
About •	paper received ※ 25 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPRB036	Study on Beam-induced heating in injection section of Hefei Light Source	vacuum, kicker, radiation, experiment	652
	D.R. Xu, W. Xu USTC/NSRL, Hefei, Anhui, People’s Republic of China
	Ceramic chambers distributed with metal belts on the inner surface are installed in the injection section at Hefei Light Source (HLS). Heating on the ceramics chambers has been observed during machine operation. An air compressor is used to cool these chambers due to concerns of overheating during top-up operation mode. To understand the sources of the heating, a series of experiments are performed with various beam currents and bunch filling patterns. The study shows that the heating is mainly caused by the narrow-band impedances of the ceramic chambers and their adjacent vacuum components.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB036
About •	paper received ※ 22 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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MOPRB057	An Approach to Alleviating Heavy Beam Loading Effect on the Synchrotron Machine Through the Existed Low Level RF Feedback System	cavity, feedback, beam-loading, simulation	697
	L.-H. Chang, F.Y. Chang, M.H. Chang, S.W. Chang, L.J. Chen, F.-T. Chung, Y.T. Li, M.-C. Lin, Z.K. Liu, C.H. Lo, Ch. Wang, M.-S. Yeh, T.-C. Yu NSRRC, Hsinchu, Taiwan
	To pursue the highest brightness and intensity of the synchrotron light, the synchrotron machines are pushed to operate with as high as possible of the beam current. To suppress the heavy beam loading effects, the direct RF feedback is currently widely used. This paper provides an another approach to alleviating the heavy beam loading effects on machine operation. Different from the direct RF feedback technique, this approach need not add additional feedback loop to the existed RF feedback system. Applying a proper angle rotation to the I-Q error signals of the cavity voltage, before entering the existed feedback loop, is the only action required in this approach. The paper will explain the working mechanism and investigate the behaviour of this approach, through an example case, with numerical simulation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB057
About •	paper received ※ 16 April 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019
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MOPTS063	Design and Low Power Test of a Prototype HOM LINAC	DTL, HOM, cavity, linac	1001
	L. Lu, T. He, C.C. Xing, L. Yang IMP/CAS, Lanzhou, People’s Republic of China L. Yang University of Chinese Academy of Sciences, Beijing, People’s Republic of China
	A 325MHz HOM (higher order mode) type linac was proposed and studied for proton or heavy ion acceleration in medium energy region. The cavity was finished the fabrication already by using copper and aluminum material. We will report results of low power test of the HOM linac in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPTS063
About •	paper received ※ 29 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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MOPTS089	Transverse Beam Dynamics Studies With High Intensity LHC Beams in the SPS	injection, octupole, emittance, electron	1062
	M. Carlà, H. Bartosik, M.S. Beck, L.R. Carver, V. Kain, G. Kotzian, K.S.B. Li, G. Rumolo, C. Zannini CERN, Geneva, Switzerland
	In order to reach the target beam parameters of the LHC injectors upgrade (LIU), about twice the presently operational intensity of LHC type beams has to be achieved. Although the planned upgrade of the main RF system will occur during the long shutdown, a series of measurements have been performed to assess the beam dynamics challenges with these very high intensity beams on the long SPS injection plateau. Bunch-by-bunch transverse emittance blow-up measurements suggested the presence of electron-cloud. After a period of running with the high intensity beam for a couple of days, a clear improvement of beam quality was observed which is attributed to scrubbing. In addition, a horizontal headtail instability is encountered for the usual operational settings of chromaticity and transverse damper. The stability limit as a function of chromaticity and Landau octupole settings has been explored and will be discussed, together with possible sources of the instability and mitigation strategies.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPTS089
About •	paper received ※ 06 May 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019
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TUZZPLS2	Beam Dynamics, Injection and Impedance Studies for the Proposed Single Pulsed Nonlinear Injection Kicker at the Australian Synchrotron	injection, kicker, synchrotron, storage-ring	1219
	R. Auchettl, R.T. Dowd, Y.E. Tan AS - ANSTO, Clayton, Australia
	The Australian Synchrotron are currently investigating the use of a single pulsed nonlinear injection kicker (NLK) to free floor space within the ring for future beamline development. The NLK has a zero and flat magnetic field at the stored beam to leave the stored beam undisturbed but has a maximum field off-axis where the injected beam is located. After the kick, the injected beam is stored. While NLKs have been prototyped at many facilities around the world, injection efficiency and heat loading have been the main impediment to deployment of the NLK. The wakefields that pass through the ceramic chamber aperture can cause severe heat loading and impedance. Despite achieving impressive injection efficiencies, a previous prototype at BESSY II * showed that strong interactions of the stored beam resulted in high heat load causing the thin 5µm Titanium coated ceramic chamber to reach temperatures > 500 °C and fail. To avoid beam induced heat loads, this paper presents studies of the wake impedance and thermal behaviour for our proposed NLK design. Injection simulations and future considerations for installation and operation at the Australian Synchrotron will be discussed. * T. Atkinson et al., "Development of a non-linear kicker system to facilitate a new injection scheme for the Bessy II storage ring", in Proc. IPAC’11, 2011, THPO024, pp. 3394-3396.
	Slides TUZZPLS2 [1.588 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUZZPLS2
About •	paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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TUPMP044	Special Aluminum Gasket Sealing of Non-circular Profile Flanges for the Accelerator UHV Systems	vacuum, photon, experiment, emittance	1347
	G.Y. Hsiung NSRRC, Hsinchu, Taiwan
	Most of the beam ducts for the accelerators are not regularly the circular profile. Unfortunately, the conflat (CF-) flanges and the gaskets with non-circular profile were not commercially available. Besides, additional RF-contact bridges between the flanges must be built in for mitigating the impedance from the flange-gaps. In this presentation, various types of the aluminum (Al-) gaskets designed for the non-circular profile Al-flanges for the accelerator ultrahigh vacuum (UHV) systems are introduced. The surface of the Al-flange is flat to accommodate the special Al-gasket with knife edges for the sealing. Both the flange and gasket are manufactured by the oil-free Ethanol-CNC-machining process that any non-circular profile, e.g. rectangular, race-track, key-hole, etc., flanges can be precisely produced. The inner diameters of the gasket just suits those of the flanges that the impedance from the gap is significantly reduced. The flanges and gaskets after oil-free machining can be assembled immediately without any chemical cleaning. The experimental results for the as-mentioned non-circular profile Al-flanges reveal the UHV quality at pressure < 20 nPa after vacuum baking.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPMP044
About •	paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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TUPGW015	Petra III Operation and Studies 2018	operation, vacuum, undulator, radiation	1419
	M. Bieler, I.V. Agapov, Y.-C. Chae, J. Keil, G.K. Sahoo, R. Wanzenberg DESY, Hamburg, Germany
	At DESY the Synchrotron Light Source PETRA III offers scientists outstanding opportunities for experiments with hard X-rays of exceptionally high brilliance since 2009. This paper describes the operational schedule, the operational statistics and the most important beam studies done at PETRA III in 2018.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW015
About •	paper received ※ 26 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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TUPGW082	Impedance of the Flange Joints With the RF Contact Spring in NSLS-II	storage-ring, vacuum, cavity, damping	1597
	A. Blednykh, B. Bacha, G. Bassi, C. Hetzel, B.N. Kosciuk, T.V. Shaftan, V.V. Smaluk, G.M. Wang BNL, Upton, Long Island, New York, USA
	Funding: This work was supported by Department of Energy Contract No. DE-SC0012704 Since the beginning of the NSLS-II commissioning, temperature of the vacuum components has been moni-tored by the Resistance Temperature Detectors located predominantly outside of the vacuum enclosure and at-tached to the chamber body. Temperature map helps us to control overheating of the vacuum components around the ring especially during the current ramp-up. The average current of 475mA has been achieved with two main 500MHz RF cavities and w/o harmonic cavities. Effect of the RF shielded flanges on local heat and on the longitu-dinal beam dynamics is discussed in details.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW082
About •	paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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TUPGW092	Working Impedance Model and Its Effect on the Intensity Limitation of Petra-IV Storage Ring	cavity, feedback, emittance, storage-ring	1623
	Y.-C. Chae DESY, Hamburg, Germany
	We made sufficient progress in modeling the imped-ance of the PETRA-IV storage ring. The result was ap-plied to estimate the impedance-based single and multi-bunch intensity limit. Due to the extremely small emit-tance of the beam the intrabeam scattering (IBS) effects will be significant unless they are reduced by bunch lengthening. The 3rd harmonic cavity was proposed to dilute the bunch density which resulted in the small syn-chrotron frequency with a large spread. Because of the complexity introduced by impedance and harmonic cavity we used broadband impedance up to 200 GHz to compute the parameters such as bunch length and energy spread at different currents. We found that the microwave instability started very early in current less than 0.5 mA. Even if it is small, the prediction by tracking simulation was consistent with another diffraction-limited storage ring (DLSR) when the Keil-Schnell criterion was used to predict one from the other. Then, we present the single-bunch current limit which had included the effect of geometric and resistive wall impedances of the NEG-coated chamber. Finally, we present the emittance and lifetime which can be realistically achieved in the ring with the above collective effects included.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW092
About •	paper received ※ 14 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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TUPGW099	Superconducting Crab Cavity Options for Short X-Ray Pulse Generation in SPEAR3	cavity, sextupole, GUI, HOM	1647
	F. Toufexis, V.A. Dolgashev, X. Huang, Z. Li SLAC, Menlo Park, California, USA
	Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515. We are exploring methods to generate short X-ray pulses in SPEAR3 on the order of 1 ps to enable studying ultrafast processes in materials. We are developing a 2-frequency crab cavity scheme with two sets of crab cavities* at the 6th and 6.5th harmonics of the 476 MHz ring RF frequency. In previous work we studied a normal conducting crab cavity for SPEAR3. In this work we explored two superconducting cavity options: a traditional elliptical cavity and the Quasi-waveguide Resonator. We found that the Quasi-waveguide Resonator cannot meet our field uniformity specifications due to higher order multipole fields. We then optimized a traditional elliptical cavity with the input, Lower Order Modes, and Higher Order Modes couplers following the Argonne Advanced Photon Source design. A. Zholents, et al, Nucl. Instrum. Methods Phys. Res., Sect. A, Vol. 425 (1999), p. 385. Z. Li, et al, Proceedings of IPAC17. * A. Lunin, et al, Proceedings of HOMSC14.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW099
About •	paper received ※ 11 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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TUPGW107	Overview of Collective Effects in SLS 2.0	cavity, operation, simulation, damping	1658
	M.M. Dehler, M. Aiba, A. Citterio, L. Stingelin PSI, Villigen PSI, Switzerland
	At the end of 2017, the conceptual design for an upgrade of the Swiss Light Source was finished, promising a 40 fold smaller emittance and a corresponding increase of the spectral brightness from the current value. From the point of view of collective effects, the main changes in the new design are a reduced chamber size, fully coated with NEG, and operation at small and negative momentum compaction with low synchrotron frequency. We give an overview of the latest results for the ring. Most critical is the threshold for the longitudinal single bunch instability. Taking into account the combined effect of wake impedances and CSR, we have to rely on bunch stretching by a higher harmonic system to achieve stable operation at nominal current.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW107
About •	paper received ※ 14 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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TUPGW108	Characterization of NEG Coatings for SLS 2.0	GUI, resonance, coupling, vacuum	1662
	M.M. Dehler, A. Citterio PSI, Villigen PSI, Switzerland S. Alberti, J.P. Hogge SPC-EPFL, Lausanne, Switzerland M. Hahn, H.P. Marques ESRF, Grenoble, France X.Y. Liu USTC/NSRL, Hefei, Anhui, People’s Republic of China
	To limit desorption and ameliorate pumping of the narrow 20 mm aperture vacuum chamber of SLS2.0, it is planned to fully coat it with nonevaporable getter (NEG) material. NEG coating can be produced with different structural characteristics, from dense films to columnar growth, with corresponding distinct electrical properties affecting the machine impedance and the instability threshold of the accelerator. In order to evaluate and characterize the coating process for geometries similar to the SLS chamber, we measured the resonance properties of coated and uncoated shorted waveguide pieces. First tests were done with standard X band waveguides at 12 and 7 GHz. Test setups using elliptical cross sections are in preparation, also for higher frequencies allowing the characterization of thin NEG layers. The final goal is to have a standardized process to test of samples coated by external producers. We describe the setups and first results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW108
About •	paper received ※ 10 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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TUPGW109	Conceptual Design of Vacuum Chamber for SPS-II Storage Ring	vacuum, storage-ring, photon, emittance	1666
	T. Phimsen, S. Chaichuay, N. Juntong, P. Klysubun, S. Prawanta, P. Sudmuang, P. Sunwong SLRI, Nakhon Ratchasima, Thailand R. Deepan, A. Khamkham Suranaree University of Technology, Nakhon Ratchasima, Thailand
	The SPS-II is a 3 GeV ultralow emittance light source which is now under studied and designed by Thailand Synchrotron Light Research Institute (SLRI). The SPS-II storage ring is based on Double-Triple Bend Achromat (DTBA) cell with a circumference of 321.3 m aiming for horizontal emittance of less than 1 nm-rad. The compact lattice leaves narrow space for vacuum components. The small gap between poles of the magnets requires narrow vacuum chambers and limits the conductance of the chambers. The chambers will be made by stainless steel with a thickness of 1.5 mm. the cross section of beam duct is 40 mm × 16 mm elliptical shape. The bending chamber is designed as a long triangular chamber such that photon absorber can be installed as far from the light source as possible to lower the power density of the heat load. The overview of designed vacuum system for the SPS-II is presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW109
About •	paper received ※ 14 May 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019
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TUPRB101	Damping Trapped Modes in an in-Vacuum Undulator at a Synchrotron Radiation Light Source	simulation, vacuum, damping, HOM	1895
	K. Tian, Z. Li, A. Ringwall, J.J. Sebek SLAC, Menlo Park, California, USA
	Funding: Work supported by US Department of Energy Contract DE-AC03-76SF00515. In this paper, we report the efforts in solving the problem of coupled-bunch instabilities caused by an in-vacuum undulator in the SPEAR3 storage ring. After exploring several approaches to reduce the strength of the trapped modes, we found that ferrite dampers were the most effective and simplest way for mode damping in our SPEAR3 in-vacuum undulator. The results of the first RF cold measurement on an in-vacuum undulator equipped with these ferrite dampers agree well with numerical simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPRB101
About •	paper received ※ 13 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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TUPTS034	Development of Low Inductance Circuit for Radially Symmetric Circuit	experiment, kicker, high-voltage, operation	2013
	T. Takayanagi, K. Horino, T. Ueno JAEA/J-PARC, Tokai-mura, Japan
	Radiation symmetric type circuits using semiconductors of SIC-MOSFETs, one of next generation semiconductors, are composed of circuits in which many semiconductor switches are multiplexed in series and in parallel. Since the lengths of all parallel circuits are equal, the output waveform will not be distorted due to timing jitter or level change. This circuit is useful for outputting the waveform of ultrafast short pulse. Therefore, we have developed a circuit that achieves further low inductance by making the power transmission circuit into a double circular ring structure equal to the coaxial shape. Compare the inductance value obtained from the structure and the output waveform. In addition, we compare the calculation and the actual measurement in the actual test and present the verification result of the developed circular ring structure.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS034
About •	paper received ※ 01 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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WEYPLS1	Building the Impedance Model of a Real Machine	simulation, wakefield, coupling, cavity	2249
	B. Salvant, D. Amorim, S.A. Antipov, S. Arsenyev, M.S. Beck, N. Biancacci, O.S. Brüning, J.V. Campelo, E. Carideo, F. Caspers, A. Farricker, A. Grudiev, T. Kaltenbacher, E. Koukovini-Platia, P. Kramer, A. Lasheen, M. Migliorati, N. Mounet, E. Métral, N. Nasr Esfahani, S. Persichelli, B.K. Popovic, T.L. Rijoff, G. Rumolo, E.N. Shaposhnikova, V.G. Vaccaro, C. Vollinger, N. Wang, C. Zannini, B. Zotter CERN, Geneva, Switzerland D. Amorim Grenoble-INP Phelma, Grenoble, France T. Dalascu EPFL, Lausanne, Switzerland M. Migliorati Sapienza University of Rome, Rome, Italy R. Nagaoka SOLEIL, Gif-sur-Yvette, France V.V. Smaluk BNL, Upton, Long Island, New York, USA B. Spataro INFN/LNF, Frascati, Italy N. Wang IHEP, Beijing, People’s Republic of China S.M. White ESRF, Grenoble, France
	A reliable impedance model of a particle accelerator can be built by combining the beam coupling impedances of all the components. This is a necessary step to be able to evaluate the machine performance limitations, identify the main contributors in case an impedance reduction is required, and study the interaction with other mechanisms such as optics nonlinearities, transverse damper, noise, space charge, electron cloud, beam-beam (in a collider). The main phases to create a realistic impedance model, and verify it experimentally, will be reviewed, highlighting the main challenges. Some examples will be presented revealing the levels of precision of machine impedance models that have been achieved.
	Slides WEYPLS1 [5.648 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEYPLS1
About •	paper received ※ 10 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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WEPMP016	The Design and Preliminary Test of a Stripline Kicker for HALS	kicker, simulation, vacuum, high-voltage	2338
	W. Liu, F.L. Shang, L. Shang, W.B. Song, Z.B. Sun USTC/NSRL, Hefei, Anhui, People’s Republic of China
	Stripline kicker is an important components of both on-axis longitudinal accumulation and on-axis swap out injection schemes in HALS (Hefei Advanced Light Source). After more than one year of R&D, construction of the first prototype is completed. The kicker performance is simulated by CST. The results show that in the range of 0~1GHz, on differential mode, S11 is less than - 23.7dB. In order to facilitate installation, the extension part and PTFE bracket were designed. The assembly of kicker and feedthrough has been tested with pulse generator and network analyser.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPMP016
About •	paper received ※ 25 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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WEPMP018	A Novel Non-Linear Strip-Line Kicker Driven by Fast Pulser in Common Mode	kicker, injection, dynamic-aperture, multipole	2345
	J. Chen, Z. Duan, L. Huo, Y. Li, H. Shi, G. Wang, L. Wang, N. Wang IHEP, Beijing, People’s Republic of China
	The next generation storage ring-based light sources adopt multi-bend achromat lattices to achieve a low emittance. The dynamic apertures of these machines are usually less than 10 mm so that the traditional pulsed local bump injection is difficult to achieve. Off-axis injection with a pulsed multipole or a non-linear kicker could be a viable solution which requires a moderate dynamic aperture of a few mm. In this paper, a novel non-linear kicker design is presented. Unlike pulsed sextupole or nonlinear kicker magnet, the nonlinear kicker we proposed is a traveling wave kicker with 2 strip-line electrodes driven by a nanosecond-level fast pulser in common mode. The disturbance to the stored beam is minimal since the perturbation is limited to the target bunch alone. Work support by NSFC(11475200 and 11675194).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPMP018
About •	paper received ※ 30 April 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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WEPMP051	Impedance Study of a New Septum Chamber of SPEAR3	septum, simulation, vacuum, storage-ring	2447
	K. Tian, J. Langton, J.J. Sebek SLAC, Menlo Park, California, USA
	Funding: Work supported by US Department of Energy Contract DE-AC03-76SF00515. A new Septum magnet and chamber has been designed for the storage ring as a part of the accelerator improvement plan for operating a lower emittance lattice in SPEAR3. Therefore it is necessary to analyze the impedance effects on the beam from the new Septum chamber. Due to the complex design at the downstream transition of the Septum chamber, the longitudinal impedance is particular of concern. In this paper, we will present numerical simulation results for this particular component as well as the general analysis for the impedance effects of the whole chamber.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPMP051
About •	paper received ※ 14 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
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WEPGW075	Coupling Impedance Studies of the Current Transformers at ALBA	resonance, cavity, simulation, factory	2647
	T.F.G. Günzel, U. Iriso, A.A. Nosych ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
	ALBA is equipped with two different current transformers (FCT and DCCT), and a third one (ICT) is now in design stage to be installed in 2019. A comparative study of the different currents transformers was carried out in order to characterize their contribution to longitudinal and transverse impedance. The gap in the vacuum chamber of the current transformers was varied in order to study its effect on the heat deposited by the beam in the corresponding device and on the resonance in the longitudinal impedance spectrum. The simulation results are compared to the experience with the existing current transformers in operation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPGW075
About •	paper received ※ 14 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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WEPRB050	Multipacting Studies of the Coaxial Coupler for BNCT DTL	multipactoring, simulation, DTL, neutron	2921
	M.X. Fan, A.H. Li, B. Li, J. Peng, P.H. Qu, A.X. Wang, Y. Wang, X.L. Xiaolei IHEP CSNS, Guangdong Province, People’s Republic of China Q. Chen, S. Fu, H.C. Liu IHEP, Beijing, People’s Republic of China X.L. Wu DNSC, Dongguan, People’s Republic of China
	Funding: Youth Innovation Promotion Association of CAS (2015011) Program for GuangDong Introducting Innovative and Enterpreneurial Teams (2017ZT07S225) Multipacting is a phenomenon in which electrons grow sharply under certain conditions in a RF structure. It may lead to the breakdown or even damage to the equipment. Therefore, it is very important to calculate the Multipact-ing range in the RF equipment design. Since the phe-nomenon is too complicated to use the formula to fully predict it, numerical simulation is employed. There are many computer codes (such as Track3P, MultiPac, CST PS, etc.) used to simulate the phenomenon, but most of them are not commercial. In this paper, theories used in coaxial line for predicting multipacting are introduced; the CST PS is chosen to simulate the multipacting of coaxial coupler for BNCT DTL; finally, methods of sup-pressing multipacting are discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB050
About •	paper received ※ 11 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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WEPRB056	Design Study of 325MHz RF Power Coupler for Superconducting Cavity	cavity, superconducting-cavity, resonance, simulation	2937
	J.Y. Yoon, H.J. Cha, S.W. Jang, E.-S. Kim, K.R. Kim, C.S. Park, S.H. Park KUS, Sejong, Republic of Korea J. Bahng Korea University Sejong Campus, Sejong, Republic of Korea K.R. Kim PAL, Pohang, Kyungbuk, Republic of Korea
	We present the design study of the RF input power coupler for 325 MHz superconducting cavities. The power coupler, based on a conventional coaxial transmission line, provides RF powers to the cavity up to 12kW in CW mode. The thermal interceptors are considered as 4.5 K and 40 K or 4.5 K and 77 K corresponding to the usage of liquid Helium only or both liquid Helium and Nitrogen for cryogenic temperature to reduce the thermal load. The transition box (T-box), which is assembled with power coupler, is designed and applied for impedance matching and inner conductor cooling.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB056
About •	paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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WEPRB066	Utilizing the High Shunt Impedance TM020-Mode Cavity in the Double RF Systems for the Storage Ring of the Thailand New Light Source	cavity, storage-ring, coupling, damping	2972
	N. Juntong, T. Phimsen SLRI, Nakhon Ratchasima, Thailand N. Chulakham, S. Malichan Udon Thani Rajabhat University, Udon Thani, Thailand
	The utilization of the TM020-mode cavity for the storage ring based light source was pioneered by SPring-8 with its high quality factor and hence its high shunt impedance. KEK-LS has also studied the possibility of using this type of cavity for their storage ring. The TM020-mode cavity has larger transverse dimension compared to the traditional TM010-mode cavity, but with its higher shunt impedance it can be designed to fit in the new low emittance storage ring regardless. The new storage ring based light source project in Thailand aims to optimum the low emittance beam in nano-meters region with the energy of 3 GeV. The TM020-mode cavity was considered as the main cavity and the harmonic cavity for the storage ring. They have been designed to have their pipe aperture fits the storage ring beam ducts. The main cavity has a high shunt impedance of 8.3 Mega Ohms with the 51,000 unloaded quality factor. The harmonic cavity has a high shunt impedance and an unloaded quality factor of 2.45 Mega Ohms and 36,000, respectively. The damping mechanism of the parasitic modes and the tuning mechanism of the operating mode of these cavities were also studied. There will be four main cavities and six harmonic cavities in the new storage ring. Detailed design and study of these cavities will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB066
About •	paper received ※ 29 April 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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WEPRB068	Ka-Band Linearizer Studies for a Compact Light Source	wakefield, klystron, FEL, flattop	2976
	A. Castilla, G. Burt, W.L. Millar Cockcroft Institute, Lancaster University, Lancaster, United Kingdom A. Latina, X. Liu, W.L. Millar, X.W. Wu, W. Wuensch CERN, Geneva, Switzerland
	Funding: This project has received funding from the European Union’s Horizon2020 research and innovation programme under grant agreement No 777431. The CompactLight project is currently developing the design of a next generation hard X-ray FEL facility, based on high-gradient X-band (12 GHz) structures, bright electron photo-injectors, and compact short period undulators. However, to improve the brightness limitations due to the non-linear energy spread of the electron bunches, a K-band (36 GHz) linearizer is being considered to provide a harmonic compensation during the bunch compression. In this paper, we analyze the feasibility of such linearizer.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB068
About •	paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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WEPRB073	CW Room Temperature Accelerating Structures	operation, electron, radiation, SRF	2990
	S.P. Antipov, P.V. Avrakhov, E. Gomez, S.V. Kuzikov Euclid TechLabs, LLC, Solon, Ohio, USA A.A. Vikharev IAP/RAS, Nizhny Novgorod, Russia
	To this day CW linear electron accelerators were based only on expensive and bulky (embedded in a cryostat) superconducting accelerating structures. CW regime can in principle be realized with normal conducting structures provided the shunt impedance is high. Such structures can be designed using dielectrics (ultra-pure ceramics in C-band and diamond in mm-waves) with ultra-low loss tangent (~10-6). The use of dielectrics allows to concentrate the electromagnetic energy density in the dielectric region and thus minimize fields and ohmic loss on metallic walls. The thermal loss in dielectric can be relatively low given the loss tangent is small. We report here the design of structures with shunt impedance on the order of 10⁴ MOhm/m, which is several orders of magnitude higher than shut impedance in copper structures in GHz and THz range. High shunt impedance makes it possible to accelerate electrons to 1 MeV using kW-level CW RF sources like magnetrons in C-band and gyrotrons in THz range. Such CW accelerators will find applications in sterilization, food irradiation, industrial radiography and cargo inspection.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB073
About •	paper received ※ 21 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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WEPRB080	Optimization of RF Cavities Using MOGA for ALS-U	cavity, simulation, controls, gun	3007
	H.Q. Feng, K.M. Baptiste, D. Li, T.H. Luo LBNL, Berkeley, California, USA H.Q. Feng, W.-H. Huang, Z.N. Liu, C.-X. Tang TUB, Beijing, People’s Republic of China
	Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 A multi-objective genetic algorithm-based optimiza-tion process has been applied to optimize the RF design of a 500 MHz main cavity and a 1.5 GHz Higher Harmon-ic Cavity (HHC) for the Advanced Light Source upgrade (ALS-U) in Lawrence Berkeley National Laboratory (LBNL). For the main cavity, a significant improvement, compared with the existing ALS cavity, has been achieved in cavity shunt impedance and power loss den-sity simultaneously. The field strengths and distribution of the optimized structure are analysed for further re-search. For the HHC, a cavity with low R/Q has been pre-liminary designed to mitigate the beam instability. This study also serves as an example of how a genetic algo-rithm can be used for optimizing RF cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB080
About •	paper received ※ 16 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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WEPRB081	Design Study on Higher Harmonic Cavity for ALS-U	cavity, higher-order-mode, simulation, wakefield	3011
	H.Q. Feng, K.M. Baptiste, S. De Santis, D. Li, T.H. Luo LBNL, Berkeley, California, USA H.Q. Feng, W.-H. Huang, Z.N. Liu, C.-X. Tang TUB, Beijing, People’s Republic of China
	Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 The ALS upgrade (ALS-U) to a diffraction-limited light source [1] depends on the ability to lengthen the stored bunches to limit the emittance growth and increase the beam life time. Higher harmonic cavities (HHCs), also known as Landau cavities, have been proposed to in-crease beam lifetime and Landau damping by lengthen-ing the bunch. We present an optimized 1.5 GHz normal conducting HHC design for the ALS-U with a supercon-ducting-like geometry using multi-objective genetic algorithm (MOGA) for lower R/Q. The optimization goal is to reach the required shunt impedance while maintain-ing a relatively high Q value of the cavities. To minimize the coupled bunch instabilities, higher-order mode (HOM) of the HHC as well as corresponding impedance are explored and characterized.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB081
About •	paper received ※ 16 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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WEPRB105	Design of an X-Band Constant Impedance LINAC for Compact Light Project	simulation, linac, quadrupole, framework	3055
	J.M. Arnesano, A. Mostacci, L. Palumbo Sapienza University of Rome, Rome, Italy M. Diomede, M. Marongiu INFN/LNF, Frascati, Italy L. Ficcadenti INFN-Roma, Roma, Italy
	Within the framework of Horizon 2020 project, Compact Light, in order to provide a high performance, high-gradient X-band technology, for the new generation of hard X-ray FEL, a travelling wave (TW) Linac, working on 2pi/3 mode at 11.9952 GHz, fed by two types of asymmetrically couplers, has been designed. The design was performed using CST Microwave Studio frequency domain solver. First, simulations have been conduct in order to obtain the best trade-off between single cell’s parameters, varying iris aperture. Then, the both couplers, with and without pumping port, has been tuned to avoid reflections at the input port. Finally, the entire structure, with 5 cells, was simulated. The main structure parameters will be present and we will also show and discuss the acceleranting gradient obtained vary with linac lenght and input power.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB105
About •	paper received ※ 15 May 2019 paper accepted ※ 24 May 2019 issue date ※ 21 June 2019
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WEPRB107	The New 1-18 MHz Wideband RF System for the CERN PS Booster	cavity, vacuum, electronics, electron	3063
	M.M. Paoluzzi, L. Arnaudon, V. Bretin, Y. Cuvet, J. Daricou, S. Energico, M. Haase, A.J. Jones, D. Landré, C. Rossi CERN, Meyrin, Switzerland C. Ohmori KEK/JAEA, Ibaraki-Ken, Japan
	The LHC Injector Upgrade (LIU) project at CERN prepares the injectors to meet the requirements of the High Luminosity LHC. For protons, it includes the new Linac4, PS Booster (PSB), PS and SPS. Among the major changes concerning the PSB, the extraction energy increase from 1.4 GeV to 2 GeV and the higher beam intensity, made possible by the Linac4 together with the new charge exchange injection system into the PSB (2·10¹³ protons) strongly affect the RF system requirements. To deal with this more demanding beam operation, a new RF system was designed. It is based on modern magnetic alloy loaded cavities driven by solid-state amplifiers. Its wideband frequency response (1 MHz to 18 MHz) covers all the required frequency schemes. This new RF system has been produced in 2017 and 2018; installation is planned during 2019, the first year of Long Shutdown 2 (LS2) and commissioning foreseen in 2020. Most of the production and testing was outsourced to industry; parts acceptance, cavities assembly and pre-testing was done in-house. A quality assurance plan was established to achieve the required high reliability. This paper describes the procurement, production and testing strategies and methodologies. It also reports the achieved results, system performances and relevant statistics.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB107
About •	paper received ※ 26 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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WEPTS012	RF Design Studies of a 1.3 GHz Normal Conducting CW Buncher for European X-FEL	multipactoring, simulation, coupling, cavity	3109
	S. Lal, Y. Chen, H.J. Qian, H. Shaker, G. Shu, F. Stephan DESY Zeuthen, Zeuthen, Germany V.V. Paramonov RAS/INR, Moscow, Russia
	A CW upgrade of European XFEL is under consideration, and CW electron injector is under R&D at DESY. One of the injector solutions is the LCLS-II like injector based on a normal conducting CW gun and buncher. RF design of a 1.3 GHz normal conducting buncher structure with accelerating voltage of ~ 400 kV, for such a CW injector is carried out at DESY Zeuthen site. The buncher structures with different geometrical shapes and numbers of cells are studied. The designs are optimized to have higher shunt impedance, higher mode separation and lower thermal power density for CW operation. Multipacting analysis and beam dynamics simulations are also presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS012
About •	paper received ※ 12 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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WEPTS049	Flat-Bottom Instabilities in the CERN SPS	simulation, HOM, feedback, LLRF	3224
	M. Schwarz, K. Iliakis, A. Lasheen, G. Papotti, J. Repond, E.N. Shaposhnikova, H. Timko CERN, Meyrin, Switzerland
	At beam intensities of 2.6·10¹¹ protons per bunch, required at SPS injection for the High Luminosity LHC beam, longitudinal instabilities can degrade the beam quality delivered by the SPS, the LHC injector at CERN. In this paper, we concentrate on beam instability at flat bottom. The dependence of the instability threshold on longitudinal emittance and LLRF system settings was measured, to help identify the impedance driving this instability. While reducing the longitudinal emittance reduces the losses at injection, it can drive the beam unstable. The LLRF system of the SPS (partially) compensates beam loading, but also affects the instability. The effect of the different LLRF systems (feedback, feedforward, phase loop and longitudinal damper) and fourth harmonic RF system on the instability was investigated. The measurements are compared with simulations performed with the longitudinal tracking code BLonD.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS049
About •	paper received ※ 10 May 2019 paper accepted ※ 19 May 2019 issue date ※ 21 June 2019
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WEPTS089	Microbunching Instability Mitigation via Multi-Stage Cancellation	bunching, electron, linac, laser	3321
	J. Qiang, B. Li LBNL, Berkeley, California, USA
	Funding: This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and used computer resources at the National Energy Research Scientific Computing Center. The microbunching instability driven by beam collective effects in the linear accelerator of a free electron laser (FEL) facility can significantly degrade electron beam quality and FEL performance. Understanding and control of the instability is a priority for the design of modern high-brightness electron accelerators. In this paper, we study an instability cancellation phenomenon due to 180 degree phase slippage of the current modulations between different amplification stages. A case study of using a nonisochronous dogleg section in a double compression scheme to cancel the current modulation is illustrated.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS089
About •	paper received ※ 07 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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WEPTS101	A General Comparison on Impedance Theory and CST Simulation of Discontinuities	simulation, vacuum, coupling, storage-ring	3352
	N. Khosravi, E. Ahmadi, M. Akhyani, S. Dastan, A.M. Mash’al ILSF, Tehran, Iran H. Karimi Isfahan University of Technology, Isfahan, Iran
	Inhomogeneity of vacuum chamber components is the main source of coupling impedance. Nowadays, wake potential is mostly predictable by 3D codes. Analytical prediction of impedance theories can be helpful as a side solution. On the other hand, some asymmetries in the geometry of components might make troubles and lead to imprecise numerical results in 3D simulations. Analytical approximation of discontinuities, holes, and grooves can give us an estimation of expected results and can be used as a benchmark in the case that we do not have any experimental data. To clarify the validity of theoretical expressions, general discontinuities are simulated in CST. The comparison of final results is presented here. At last, resistive wall impedance and some general discontinuities of components at ILSF storage ring are compared from the theoretical and simulation point of view.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS101
About •	paper received ※ 01 May 2019 paper accepted ※ 24 May 2019 issue date ※ 21 June 2019
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THPGW033	Numerical Study of Photonic-Crystal-Based Dielectric Accelerators	GUI, photon, acceleration, electron	3653
	G. Torrisi, L. Celona, S. Gammino, D. Mascali, G. Sorbello INFN/LNS, Catania, Italy C. De Angelis, A. Locatelli University of Brescia, Brescia, Italy G.S. Mauro INFN/LNL, Legnaro (PD), Italy G. Sorbello University of Catania, Catania, Italy
	All-dielectric electromagnetic band gap (EBG) waveguides structures promise significant improvement of accelerating gradient of laser-driven acceleration with the potential to miniaturize the accelerator itself. In this work we study photonic crystal structures designed for acceleration of relativistic electrons. We explore the performance of the all-dielectric EBG accelerating waveguide structures thanks to full wave electromagnetic simulations of couplers and accelerating waveguides. The characteristic interaction impedance, accelerating gradient and all the key parameters that are typically used to characterize linear accelerators are evaluated and used to compare the properties of the accelerating mode field distribution in different geometries.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPGW033
About •	paper received ※ 30 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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THPRB026	A 300 mm Long Prototype Strip-Line Kicker for the Heps Injection System	kicker, vacuum, injection, simulation	3864
	L. Wang, J. Chen, L. Huo, P. Liu, H. Shi, X.L. Shi, G. Wang, N. Wang IHEP, Beijing, People’s Republic of China
	In the High Energy Photon Source (HEPS), the dynamic aperture of machine is not large enough for off-axis injec-tion for its baseline 7BA lattice design. So, a group of superfast kickers with about 12 ns pulse bottom width are needed for on-axis swap out injection scheme. The design about a couple sets of 300 mm long strip-line kickers is presented. Five kickers as a module are placed in a stain-less steel vacuum vessel to solve the problem of longitu-dinal space restriction in injection area. So far, the proto-type development of strip-line kicker was completed. The results of time-domain reflectometer (TDR) test and high voltage pulse test show that the strip-line kicker can meet the requirement of the HEPS.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB026
About •	paper received ※ 06 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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THPRB049	MODELING AND SIMULATION FOR MULTI-FEEDING CAVITY WITHOUT BEAM LOADING	cavity, electron, simulation, beam-loading	3921
	K. Liu, Q. Gu, L. Li, Ch. Wang, M.H. Zhao SINAP, Shanghai, People’s Republic of China Q. Gu SSRF, Shanghai, People’s Republic of China
	The Multi-feeding cavity usually be applied in super-conducting and normal-conducting RF cavity. The differences between multiple input couplers in coupler coefficient, incident power and phase will cause the cavity field stabilities can not meet the requirements. For explore the influences of these differences and develop equations for measurement, a multi-feeding LCR transient model was developed. As two-feeding cavity, the VHF photocathode electron gun was model and simulated in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB049
About •	paper received ※ 06 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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THPRB054	Design of a Ultrafast Stripline Kicker for Bunch-by-Bunch Feedback	kicker, FEL, feedback, HOM	3931
	J. Wang, P. Li, D. Wu, D.X. Xiao, L.G. Yan CAEP/IAE, Mianyang, Sichuan, People’s Republic of China
	Lorentz force detuning and beam loading effect of the rf cavities will induce a slope of the cavity gradient. Combed with the cavity misalignments, transverse position of subsequent bunches will differ from each other. The CAEP THz Free Electron Laser facility(CTFEL) will have a fast transverse bunch-by-bunch feedback system on its test beamline, which is used to correct the beam position differences of individual bunches in the macro-pulses. The time response of the kicker is rigid for the interval of the micro-pulses is 18.5ns and will upgrade to about 2 ns, requiring impedance matching of the kicker with the power source and transmission system in a high bandwidth. Also, the electromagnetic field must reach the requirements of the beam parameters. In this paper, the structure design and the optimization of the geometric parameters of the ultrafast stripline kicker is presented. The characteristic impedance, transmission characteristics, field consistency are analyzed and optimized. And the feedback signal generation scheme for continuous bunch trains was proposed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB054
About •	paper received ※ 14 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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THPRB075	Transverse Impedance Measurements and Simulations of the LHC Injection Kicker Magnet	simulation, kicker, injection, coupling	3986
	V. Vlachodimitropoulos, M.J. Barnes, A. Chmielinska, L. Ducimetière CERN, Geneva, Switzerland A. Chmielinska EPFL, Lausanne, Switzerland
	Kicker magnets contribute significantly to the total impedance budget of many accelerators. Of particular interest, from a beam stability point of view, is the transverse beam coupling impedance (TBCI) that is used to determine intensity limitations of a machine. Until recently, no conclusive TBCI data for the Large Hadron Collider (LHC) injection kicker magnets (MKIs) was available. However, in view of the upgrade of the MKIs for the High-Luminosity LHC (HL-LHC) project, the TBCI of the existing design needed to be estimated to be used as reference for an upgraded version. To that end, electromagnetic simulations were carried out to determine the dipolar and quadrupolar components of the TBCI in the two transverse planes. To validate the simulations, test bench measurements were performed using standard RF measurement techniques. In the present work, the results from TBCI simulations and measurements are reported and compared. Detailed descriptions of the methods and techniques used as well as the realization of the experimental set-up are also given.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB075
About •	paper received ※ 14 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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THPRB092	Reduction of Beam Induced RF-Heating in the Horizontal Stripline Kicker at the TPS	kicker, storage-ring, feedback, damping	4035
	P.J. Chou, C.K. Chan, C.-C. Chang, K.T. Hsu, K.H. Hu, C.K. Kuan, I.C. Sheng NSRRC, Hsinchu, Taiwan
	In preparation for 500 mA operation at the Taiwan Pho-ton Source (TPS), we redesigned the horizontal stripline kicker for the beam feedback system to gain a smaller loss factor with higher shunt impedance. We introduced ground fenders (see Fig. 1) to this new design which resulted in the reduction of the loss factor and substantial increase of the kicker shunt impedance. The transverse profile of the kicker electrodes was matched to the race-track beam pipe in the straight sections to minimize broadband impedance. The ground fenders can reduce the leakage of image currents through the gaps between the two strip line electrodes and also help to achieve a better impedance matching for the TEM modes in the transmission lines formed by the stripline electrodes and beam pipe in the kicker. The RF design and analysis of trapped resonant modes in the kicker were simulated by the 3-D electromagnetic code GdfidL [1]. Results of the RF design and analysis of trapped resonant modes will be discussed together with analytical estimates of coupled bunch instabilities at a beam current of 500 mA.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB092
About •	paper received ※ 17 April 2019 paper accepted ※ 19 May 2019 issue date ※ 21 June 2019
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THPTS013	Further Designs of HOM Couplers for Superconducting 400 MHz RF Cavities	cavity, HOM, simulation, proton	4132
	N.F. Petry, M. Busch, K. Kümpel, O. Meusel, H. Podlech IAP, Frankfurt am Main, Germany
	The Future Circular Collider (FCC) is one possible future successor of the Large Hadron Collider (LHC) at CERN. The proton-proton collider center-of-mass collision energy is set to 100 TeV with a beam current of 0.5 A. To achieve this energy a stable acceleration is critical and therefore higher order modes (HOM) need to be damped. HOM dampers, further characterized as couplers, need to fulfill several criteria to be efficient. As a first property the couplers should assure a longitudinal impedance of higher order modes of below 10 kW. Furthermore, the loaded Q-factor should be below 1000 and the corresponding R/Q value should be in the range of 10 Ω. Besides the Hook-type and Probe-type HOM coupler two additional designs were simulated. The recent results of the different couplers attached to a superconducting 400 MHz RF cavity will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPTS013
About •	paper received ※ 09 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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THPTS039	DESIGN OF A COMPACT VARIABLE X-BAND RF POWER SPLITTER	GUI, klystron, electron, network	4194
	F. Liu, H.B. Chen, J.Y. Liu, Z.N. Liu, J. Shi, H. Zha TUB, Beijing, People’s Republic of China
	This paper presents a design of a compact variable X-band RF power splitter. The RF power splitter includes one input port and two output ports, and the power divi-sion ratio can be adjusted by changing the position of a short circuit piston. This system keeps a good match (less than -40 dB) at any power division ratio. An E-bend waveguide structure is selected to make the geometry more compact (11cm in length, 3.5cm in width and 5 cm in height). Special studies was conducted to sustain a low surface electrical field (maximum 65 MV/m at 100 MW input), and large bandwidth (250MHz). This power split-ter is designed for high-power test stand at Tsinghua Uni-versity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPTS039
About •	paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
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THPTS065	Analysis on the Thermal Response to Beam Impedance Heating of the Post Ls2 Proton Synchrotron Beam Dump	simulation, proton, site, wakefield	4260
	L. Teofili, F. Giordano, I. Lamas, F.-X. Nuiry, G. Romagnoli, B. Salvant CERN, Geneva, Switzerland M. Marongiu, M. Migliorati Sapienza University of Rome, Rome, Italy
	The High Luminosity Large Hadron Collider (HL-LHC) and the LIU (LHC-Injection Upgrade) projects at CERN are upgrading the whole CERN accelerators chain, increasing beam brightness and intensity. In this scenario, some critical machine components have to be redesigned and rebuilt. Due to the increase in beam intensity, minimizing the electromagnetic interaction between the beam and the device is a crucial design task. Indeed, these interactions could lead to beam instabilities and excessive thermo-mechanical loadings in the device. In this context, this paper presents an example of multi-physics study to investigate the impedance related thermal effects. The analysis is performed on the conceptual design of the new proton synchrotron (PS) internal dump.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPTS065
About •	paper received ※ 26 April 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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THPTS095	High Efficiency High Power Resonant Cavity Amplifier For PIP-II	cavity, coupling, network, operation	4335
	M.P.J. Gaudreau, D.B. Cope, E.G. Johnson, M.K. Kempkes, R.E. Simpson, N.A. Stuart Diversified Technologies, Inc., Bedford, Massachusetts, USA
	Funding: Work 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 70% efficiency, at 675 watts per transistor at 650 MHz. The patent pending design simplifies solid-state transmitters to create straightforward scaling to 200 kW and higher high power levels. A crucial innovation is the reliable "soft-failure" mode of operation; a failure in one or more of the transistors has negligible performance impact. This design couples the transistor drains directly to the cavity without first transforming to 50 Ohms, avoiding the circulators, cables, and connectors that would normally be required. Under an ongoing SBIR grant from the US Department of Energy, DTI designed the system to accommodate over 96 transistors in each 50 kW cavity, with minimal RF, DC, and cooling connections. By the end of the SBIR, DTI will build and demonstrate a complete 100 kW-class (~200 kW) transmitter by combining four cavity modules to show the expandability of the design to very high power levels, comparable to large VEDs.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPTS095
About •	paper received ※ 19 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
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Paper

Title

Other Keywords

Page

MOPGW001

Design Review of Bellows RF-Shielding Types and New Concepts for Sirius

shielding, storage-ring, wakefield, HOM

53

H.O.C. Duarte, P.P.S. Freitas, A.R.D. Rodrigues, R.M. Seraphim, T.M. da Rocha
LNLS, Campinas, Brazil

Large amounts of bellows in an accelerator justify the importance of simplifying the machining and assembling processes of their RF shield. Such quantity also makes this component one of the main contributors for a machine impedance budget. On the other hand, low impedance designs tend to complicate the mechanical aspects. Applied to Sirius round vacuum chamber of 24 mm inner diameter, the omega-strip and comb-type bellows concepts are compared with new proposed designs. In such comparison, the aforementioned aspects, wakefield losses and prototyping experiences are presented in this work.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW001

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paper received ※ 16 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW003

Collective Instability Studies for Sirius

simulation, storage-ring, radiation, coupling

61

F.H. de Sá
LNLS, Campinas, Brazil

In this work we will present the estimates of single and multi-bunch instability thresholds and current-dependent effects, such as tune-shifts and potential-well distortion for the Sirius storage ring. The results were obtained by tracking simulations and semi-analytic methods using the updated and detailed impedance budget of the machine, which includes contributions from all the in-vacuum components and the coherent synchrotron radiation (CSR) impedance.

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paper received ※ 15 May 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019

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MOPGW035

Coupling Impedance of the Collimator Without RF-Shields at the RCS in J-PARC

simulation, synchrotron, collimation, proton

163

Y. Shobuda, J. Kamiya, K. Moriya, K. Okabe
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan

All holes on the chamber walls of synchrotrons should be filled with the radiofrequency (RF)-shields to suppress coupling impedances that excite beam instabilities. In a synchrotron, titanium nitride (TiN)-coated RF-shields are installed with collimators. If the holes, through which the collimator jaw enters and exits the chamber, are filled with such RF-shields, the shields may break down as the dynamic coefficient of TiN increases in vacuum. At the Rapid Cycling Synchrotron (RCS), the RF-shields are eliminated from the collimator after demonstrating that the effect due to the RF-shields is negligible on the impedance at low frequencies.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW035

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paper received ※ 28 April 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019

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MOPGW036

Studies on Coherent Multi-Bunch Tune Shifts with Different Bunch Spacing at the J-PARC Main Ring

space-charge, proton, operation, injection

167

A. Kobayashi, S. Igarashi, Y. Sato, T. Shimogawa, Y. Sugiyama, T. Toyama, M. Yoshii
KEK, Tokai, Ibaraki, Japan

At a high-power proton synchrotron, betatron tune shifts induced by space charge effects cause beam loss which limits the beam intensity. To achieve further high beam intensity at the main ring of the Japan Proton Accelerator Research Complex, precise control of the tune shift is indispensable. When carrying out multi-bunch measurements, we observed that the dependence of the tune shift intensity on the number of bunches follow opposite slope trends for the horizontal and vertical directions. The influence of the bunch spacing was also observed. We report on a simplified tune shift model reconstruction for understanding the origin of these phenomena and present a correction of the tune shifts for reducing beam loss up to 30 %.

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paper received ※ 01 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW037

Dynamic Variation of Chromaticity for Beam Instability Mitigation in the 3-GeV RCS of J-PARC

simulation, emittance, extraction, injection

171

P.K. Saha, H. Harada, H. Hotchi, Y. Shobuda, T. Takayanagi, F. Tamura, Y. Watanabe
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan

We have studied many other dynamic approaches from that reported in the IPAC 2018 for transverse beam instability mitigation in the presence of strong space charge in the 3-GeV RCS of J-PARC. One of such a method is the introduction of an excess of chromaticity from that of natural chromaticity by reversing the sextupole magnetic fields from the middle of the acceleration cycle. The benifits of this method are twofold. It allows to utilize sextupole for chromaticty correction at lower energy and also mitigate the beam instability at higher energy because of introducing higher chromaticity. We first carried out numerical simulations by using ORBIT code, experimentally verified and then applied for the machine operation. The detail of simulation and measurements results are presented in this paper.

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paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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MOPGW039

Investigation of Longitudinal Beam Dynamics With Harmonic Cavities by Using the Code Mbtrack

cavity, operation, synchrotron, beam-loading

178

N. Yamamoto
KEK, Ibaraki, Japan
A. Gamelin, R. Nagaoka
SOLEIL, Gif-sur-Yvette, France

In diffraction-limited light sources, the study of collective effects is essential. With harmonic cavities (HCs), the ’flat potential condition’ can be achieved, lengthening the bunch by a factor of ~5. However, the effective rf voltage seen by the beam becomes sensitive to both positions and distributions of all bunches, as the beam-induced voltage of both HCs and fundamental cavities (FCs) contribute. In addition, when there are empty buckets, the transient beam loading induces considerable variations of the rf voltage impacting the beam performance*. Here the use of analytical approaches is difficult. Then we introduced the new functions to treat the high-Q resonators driven by either or both of the beams and external generators to the code mbtrack**. Using these features, various operating conditions with arbitrary fill patterns can be studied; coupled bunch instability induced by HOMs of the cavity, Robinson instabilities and general beam dynamics with HCs. The growth rates of the instabilities described above are compared with analytical results. The ring performance with HCs in several fill patterns shall be also reported.
* N.Yamamoto, et al., PRAB, 21, 012001 (2018).
**G. Skripka, et al., NIM A806, 221 (2016).

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paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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MOPGW052

The Study of Single-Bunch Instabilities in the Ramping Process in the HEPS Booster

booster, simulation, lattice, injection

206

H.S. Xu, Y.M. Peng, N. Wang
IHEP, Beijing, People’s Republic of China

The booster of High Energy Photon Source (HEPS) is proposed to ramp the beam energy from 500 MeV to 6 GeV, and to deliver the required charge to the storage ring. However, the transverse single-bunch instability may limit the reachable bunch charge in the booster. The study of the transverse single-bunch instability has been carried out for the HEPS booster at both 500 MeV and 6 GeV to double check whether the required single-bunch charge can be achieved. Furthermore, the energy ramping process was recently included in the study. We concentrate in the analyses of the simulation results with the consideration of energy ramping process in this paper.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW052

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paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW058

Towards a Sextupole-Free Electron Storage Ring

electron, vacuum, storage-ring, feedback

217

T.-Y. Lee, T. Ha
PAL, Pohang, Kyungbuk, Republic of Korea

This paper studies if it is possible to build an electron storage ring with no or a small number of sextupole mag-nets. If it is possible, the electron storage ring will be great-ly simplified. For the purpose, two methods are presented in the paper to handle head-tail instability: One is to use dielectric vacuum chamber made of such materials as ceramic or glass to reduce broadband impedance signifi-cantly. Then head-tail instability would be extremely weak. The other method is to install a bunch-by-bunch feedback system to suppress the already weak head-tail instability due to the dielectric vacuum chamber.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW058

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paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW064

On Wakefield in Dielectric Waveguide with Shallow Corrugation of Metallic Wall

GUI, radiation, ECR, wakefield

237

A.V. Tyukhtin, E.R. Akhmatova, T.Yu. Alekhina, S.N. Galyamin, V.V. Vorobev
Saint Petersburg State University, Saint Petersburg, Russia

Funding: This work was supported by the Russian Science Foundation (Grant # 18-72-10137).
Bunch radiation in periodical waveguides was mainly analyzed for situations when wavelengths are comparable to the structure period (Smith-Purcell emission). However, it is also of interest to study the "long-wave radiation" with wavelengths which are much larger than the structure period*,**. In such situation, the exact boundary conditions on the complicated periodic surface can be replaced with the equivalent boundary conditions (EBC) which must be fulfilled on the smooth surface. Earlier we considered with this approach radiation of the bunch moving along the axis of circular vacuum corrugated waveguide**. Comparison of analytical results with COMSOL simulations showed high accuracy of the EBC method. Here we analyze an analogous problem for the waveguide with corrugated wall and dielectric filling under condition that Cherenkov effect takes place in the dielectric. Due to this fact the radiation differs radically from that in the vacuum waveguide. At the same time, the radiation has essential differences from the one in the usual dielectric waveguide. The radiation properties in the waveguide under consideration and its differences from the radiation in the waveguide with smooth wall are analyzed.
* G. Stupakov, K. Bane, Phys. Rev. ST-AB, 15 (2012) 124401.
** A.V. Tyukhtin et al, J. of Instrumentation, 13 (2018) C04009.

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paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW066

Local Impedance Measurements Using the Orbit Bump Method at ALBA

storage-ring, betatron, simulation, vacuum

240

Z. Martí, G. Benedetti, T.F.G. Günzel, U. Iriso
ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain

The orbit bump technique has been used at the ALBA Storage Ring to characterize with good precision the impedance of single machine elements, like the in-vacuum undulators or the CLIC stripline kicker. The results are compared with theoretical studies, as well as impedance measurements done at ALBA using other methods like the turn by turn betatron phase or from the analysis of the detuning slopes of the Transverse Mode Coupling Instability.

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paper received ※ 14 May 2019 paper accepted ※ 17 May 2019 issue date ※ 21 June 2019

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MOPGW068

Crosstalk of Beam-Beam Effect and Longitudinal Impedance at CEPC

simulation, luminosity, collider, factory

247

Y. Zhang, N. Wang, C.H. Yu
IHEP, Beijing, People’s Republic of China
C.T. Lin
University of Chinese Academy of Sciences, Beijing, People’s Republic of China

Funding: Project 11775238 supported by NSFC
In conventional e⁺e⁻ storage ring colliders, we only use lengthend bunch length in beam-beam simulation instead of considering impedance directly. It is no problem since the longitudinal dynamics is not sensitive to beam-beam interaction. But it is different since the bunch will also be lengthend during beam-beam interaction by beamstrahlung effect. It is very natural and more self-consistent to consider the longitudinal impedance in the beam-beam simulation. The simulation shows that the working point region of stable collision is slightly shifted by the longitudinal impedance. It is found that the vertical coherent oscillation may decreases the beam-beam limit with impedance at some working point.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW068

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paper received ※ 15 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW074

New Spiral Beam Screen Design for the FCC-hh Injection Kicker Magnet

kicker, injection, coupling, vacuum

270

A. Chmielinska, M.J. Barnes
CERN, Geneva, Switzerland

The injection kicker system for the Future Circular Collider (FCC-hh) must satisfy demanding requirements. To achieve low pulse ripple and fast field rise and fall times, the injection system will use ferrite loaded transmission line type magnets. The beam coupling impedance of the kicker magnets is crucial, as this can be a dominant contribution to beam instabilities. In addition, interaction of the high intensity beam with the real part of the longitudinal beam coupling impedance can result in high power deposition in the ferrite yoke. This gives a significant risk that the ferrite yoke will exceed its Curie temperature: hence, a suitable beam screen will be a critical feature. In this paper, we present a novel concept - a spiral beam screen. The fundamental advantage of the new design is a significant reduction of the maximum voltage induced on the screen conductors, thus decreased probability of electrical breakdown. In addition, the longitudinal beam coupling impedance is optimized to minimize power deposition in the magnet.

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paper received ※ 26 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW076

Verification by RF Measurements of New HOM Mitigation Scheme Developed for Future SPS 33-Cell Accelerating Structures

HOM, damping, simulation, coupling

274

P. Kramer, A. Farricker, C. Vollinger
CERN, Geneva, Switzerland

Longitudinal higher-order modes (HOMs) at a frequency of around 630 MHz in the 200 MHz travelling wave RF structures currently limit the beam intensities in the CERN SPS to less than that required by the High Luminosity (HL-) LHC. In the framework of the LHC Injectors Upgrade (LIU) project, the performance of the already existing HOM damping scheme for these standing wave modes must be improved. This involves improving the existing HOM-couplers as well as the possible use of a new mitigation technique via the insertion of resonant posts in some cells of the multi-cell structures. The development of the new damping scheme has been performed using theoretical analysis of the cavity-coupler interaction in conjunction with full-wave electromagnetic (EM) field simulations. This contribution will show the verification of the improved HOM damping performance by measurements on a single section with 11 cells and on the future 33-cell structures. The parasitic impact of the damping scheme on the travelling wave fundamental passband (FPB) will also be presented.

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paper received ※ 11 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW077

Impedance Reduction in the CERN SPS Through Element Layout Optimisation

coupling, extraction, cavity, quadrupole

277

A. Farricker, C. Vollinger
CERN, Geneva, Switzerland

The CERN accelerator complex is currently in its long shutdown while the LHC Injector Upgrade is being carried out. The upgrade of the SPS includes but is not limited to: the relocation of the beam dumping system, upgrade of the RF system, replacement of the electrostatic septa and impedance reduction. These major upgrades present an opportunity to perform additional impedance reduction in areas not normally modified due to the large amount of work being performed across the accelerator complex. In this paper, we look at the impedance minimization in the sections near the large aperture quadrupoles of the extraction regions in the CERN SPS. By optimizing the locations of existing equipment and the introduction of a new, more impedance optimised type of bellows, significant reductions in the beam-coupling impedance can be achieved.

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paper received ※ 08 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW083

Longitudinal Coupled-Bunch Instability Evaluation for FCC-hh

emittance, cavity, HOM, synchrotron

297

I. Karpov, E.N. Shaposhnikova
CERN, Meyrin, Switzerland

High-order modes (HOM) of the accelerating rf structures and other machine elements, if not sufficiently damped, can drive longitudinal coupled-bunch instabilities (CBI). Their thresholds can be accurately obtained from macro-particle simulations using the detailed impedance model containing many different contributions. This method, however, is very difficult to apply for synchrotrons with a large number of bunches, as it is the case for the Future Circular hadron-hadron Collider (FCC-hh) with up to 10400 circulating bunches per beam. In this paper the semi-analytical approach is used for calculations of the instability thresholds during the acceleration cycle of the FCC-hh. As the result, we define requirements for the HOM damping that would be sufficient to prevent development of longitudinal CBI in the presence of weak synchrotron radiation damping.

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paper received ※ 13 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW084

Beam Loading Compensation for the Future Circular Hadron-Hadron Collider (FCC-hh)

cavity, beam-loading, hadron, collider

301

I. Karpov, P. Baudrenghien
CERN, Meyrin, Switzerland

The power consumption of the rf system can be minimised by optimising the cavity detuning and the loaded quality factor. In high-current accelerators, the presence of gaps in the filling results in a modulation of the cavity voltage along the ring (transient beam loading) and as a consequence a spread in the bunch parameters. In addition longitudinal coupled-bunch instabilities can appear, caused by the cavity impedance at the fundamental. Both issues can be mitigated by using an rf feedback around the amplifier and cavity, a technique used in many high intensity machines including the Large Hadron Collider (LHC). Compared to the LHC machine, the energy increase and the radiation loss for the Future Circular hadron-hadron Collider (FCC-hh) will be larger, resulting in a synchronous phase deviating significantly from 180 degrees. The solutions adopted for the LHC must therefore be revisited. This paper evaluates several beam loading compensation schemes for this machine.

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paper received ※ 13 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW087

GALACTIC and GALACLIC: Two Vlasov Solvers for the Transverse and Longitudinal Planes

synchrotron, resonance, simulation, coupling

312

E. Métral
CERN, Geneva, Switzerland

GALACTIC and GALACLIC, two Vlasov solvers for the study, in the transverse and longitudinal plane respectively, of single-bunch coherent oscillation modes, were recently developed starting from the Vlasov equation and using a decomposition on the low-intensity eigenvectors, as proposed by Laclare and Garnier. The first Vlasov solver was used for instance to shed light on the destabilising effect of resistive transverse dampers and the second helped understanding the details of the mode-coupling behind some longitudinal microwave instabilities. Both theories are reviewed in detail, highlighting in particular the similarities and peculiarities of the two approaches.

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paper received ※ 23 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPGW088

A Two-Mode Model to Study the Effect of Space Charge on TMCI in the "Long-Bunch" Regime

coupling, space-charge, optics, simulation

316

E. Métral
CERN, Geneva, Switzerland

Using a two-mode approach for the Transverse Mode-Coupling Instability (TMCI) in the ’short-bunch’ regime (where the mode-coupling takes place between the modes 0 and -1, such as in the CERN LHC), both a reactive damper (ReaD) and Space Charge (SC) are expected to be beneficial: the ReaD would shift the mode 0 up while SC would shift the mode -1 down, but in both cases the coupling (and related instability) would occur at higher intensities. However, the situation is more involved in the ’long-bunch’ regime (where the mode-coupling takes place between higher-order modes, such as in the CERN SPS). As the ReaD modifies only the (main) mode 0 and not the others, it is expected to have no effect for the main mode-coupling. As concerns SC, it modifies all the modes except the mode 0, and the result has been a subject of discussion for two decades. A two-mode approach is discussed in detail in this contribution for the case of a single bunch interacting with a broad-band resonator impedance in the ’long-bunch’ regime. This model reveals in particular that in the presence of space charge, the intensity threshold can only be similar to or lower than that in the absence of space charge.

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paper received ※ 23 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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MOPGW089

Longitudinal Mode-Coupling Instability: GALACLIC Vlasov Solver vs. Macroparticle Tracking Simulations

simulation, coupling, synchrotron, proton

320

E. Métral
CERN, Geneva, Switzerland
M. Migliorati
Rome University La Sapienza, Roma, Italy
M. Migliorati
INFN-Roma1, Rome, Italy

Following the same approach as for the recently developed GALACTIC Vlasov solver in the transverse plane and taking into account the potential-well distortion, a new Vlasov solver, called GALACLIC, was developed for the longitudinal plane. In parallel, a new mode analysis was implemented for the post-processing of the results obtained through macroparticle tracking simulations. The results of the several benchmarks performed between the two methods are presented.

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paper received ※ 23 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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MOPGW091

Capture and Flat-Bottom Losses in the CERN SPS

beam-loading, injection, emittance, feedback

327

M. Schwarz, A. Lasheen, G. Papotti, J. Repond, E.N. Shaposhnikova, H. Timko
CERN, Meyrin, Switzerland

Particle losses on the flat bottom of the SPS, the last accelerator in the injector chain of the LHC at CERN, are a strong limitation for reaching the high intensities required by the high luminosity upgrade of the LHC. Two contributions to these losses are investigated in this paper. The first losses occur during the PS-to-SPS bunch-to-bucket transfer, since the bunch rotation in the PS creates halo particles and the bunch does not completely fit into the SPS RF-bucket. The effect of longitudinal shaving in the PS on the beam transmission was recently tested. At high intensities, further capture losses are caused by beam loading in the traveling wave RF system of the SPS, which is partially compensated by the LLRF system, in particular by one-turn delay feedback. While the feedforward system reduces the capture losses, it also increases the losses along the flat bottom due to the RF noise.

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paper received ※ 09 May 2019 paper accepted ※ 19 May 2019 issue date ※ 21 June 2019

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MOPGW099

Vlasov-Fokker-Planck Simulations of Passive Higher-Harmonic Cavity Effects in ALS-U

cavity, simulation, synchrotron, resonance

357

G. Bassi
BNL, Upton, Long Island, New York, USA

Funding: Work supported by DOE under contract DE-SC0012704
We discuss numerical simulations of the Vlasov-Fokker-Planck equation to model passive higher-harmonic cavity (HHC) effects with parameters of the Advanced Light Source Upgrade (ALS-U. The numerical results, obtained with the SPACE code, are compared with a modal analysis of the coupled-bunch instability theory.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW099

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paper received ※ 18 May 2019 paper accepted ※ 24 May 2019 issue date ※ 21 June 2019

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MOPGW122

Beam-based Measurement of Broadband Longitudinal Impedance at NSLS-II

vacuum, simulation, diagnostics, storage-ring

400

V.V. Smaluk, B. Bacha, G. Bassi, A. Blednykh
BNL, Upton, Long Island, New York, USA

Funding: Department of Energy Contract No. DE-SC0012704
Interaction of a particle beam with the vacuum chamber impedance is one of the main effects limiting the beam intensity in accelerators. Minimization of the impedance is an essential part of the vacuum chamber design for any new accelerator project. The impedance can be estimated experimentally by measuring beam dynamics effects caused by the beam-impedance interaction. Experience obtained at many accelerator facilities shows the beam-based measurements are often different from the pre-computed impedance budgets, the discrepancy of a factor of two or even more is not unusual. The measurements of broadband longitudinal impedance carried out at NSLS-II are discussed in comparison with the numerically simulated impedance budget.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW122

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paper received ※ 15 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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MOPMP037

Updated High-Energy LHC Design

injection, emittance, proton, damping

524

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, J. Keintzel, R. Kersevan, V. Mertens, J. Molson, 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, A. Abramov, E. Cruz Alaniz, H. Pikhartova, 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

Funding: This work was supported in part by the European Commission under the HORIZON 2020 project ARIES no.730871, and by the Swiss Accelerator Research and Technology collaboration CHART.
We present updated design parameters for a future High-Energy LHC. A more realistic turnaround time has led to a revision of the target peak luminosity, as well as a choice of a larger IP beta function, and longer physics fills. Pushed parameters of the Nb₃Sn superconducting cable together with a modified layout of the 16 T dipole magnets resulted in revised field errors, updated dynamic-aperture simulations, and an associated re-evaluation of injector options. Collimators in the dispersion suppressors help achieve satisfactory cleaning performance. Longitudinal beam parameters ensure beam stability throughout the cycle. Intrabeam scattering rates and Touschek lifetime appear benign.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPMP037

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paper received ※ 10 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPRB006

HOM Damping Options for the Z-Pole Operating Scenario of FCC-ee

HOM, cavity, damping, dipole

590

S. Gorgi Zadeh
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
R. Calaga
CERN, Meyrin, Switzerland
T. Flisgen
FBH, Berlin, Germany
U. van Rienen
University of Rostock, Rostock, Germany

The Z-pole option of FCC-ee is an Ampere class machine with a beam current of 1.39 A. Due to high HOM power and strong HOM damping requirements, the present baseline of FCC-ee considers a single cell cavity at 400 MHz. In this paper, different HOM damping schemes are compared for the Z-pole operating scenario with the aim of lowering the parasitic longitudinal and transverse impedance. The HOM power for each damping scheme is also calculated.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB006

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paper received ※ 15 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPRB018

Conceptual Design of Negative-Muon Decelerator for Material Science

cavity, induction, experiment, power-supply

610

C. Ohmori, M. Otani, K. Shimomura
KEK, Tokai, Ibaraki, Japan
T. Takayanagi
JAEA/J-PARC, Tokai-mura, Japan

In 2018, a Negative-Muon Spin Rotation and Relaxation technique was developed in J-PARC Material and Life Science Facility. It is a novel scheme to investigate the motion of hydrogens in the chemicals and materials. To study small samples, the surface of materials and thin foils, a low energy negative muon beam is required. To decelerate intense 300-keV muons to 15-keV, we propose a system which consists of pulse generators and multi-gap induction decelerators. In this design, an inductive adder scheme is considered to use for the high voltage pulse source. High impedance magnetic alloy ring cores will be loaded in the decelerator cells. The high impedance cores which have much larger size than those for public use were developed for J-PARC RF systems and used for many applications including CERN booster RF, anti-proton deceleration and medical accelerator. In this paper, we present a conceptual design of muon deceleration system.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB018

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paper received ※ 13 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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MOPRB033

Preliminary Research of HOM for 100MHz Superconducting Cavity in the Pre-Research Project of HALS

HOM, cavity, damping, simulation

649

Y.G. Tang, L. Wang, C.-F. Wu
USTC/NSRL, Hefei, Anhui, People’s Republic of China

A 100MHz QWR superconducting cavity is researched in the pre-research project of Hefei Advanced Light Source (HALS). Higher order modes (HOM) damping is a big challenge for synchrotron radiation light source. In this paper, we first apply the novel choke mode structure to the 100MHz QWR (quarter wave resonator) cavity in order to damp the HOM. We identify the main harmful higher order modes. The HOMs in the QWR cavity are suppressed by optimizing the choke dimensions. The broadband HOM impedance spectrum of the cavity was also evaluated by calculating the beam induced wake potential in time domain. The results show that choke mode structure has a good HOM damping effect on the QWR cavity.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB033

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paper received ※ 25 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPRB036

Study on Beam-induced heating in injection section of Hefei Light Source

vacuum, kicker, radiation, experiment

652

D.R. Xu, W. Xu
USTC/NSRL, Hefei, Anhui, People’s Republic of China

Ceramic chambers distributed with metal belts on the inner surface are installed in the injection section at Hefei Light Source (HLS). Heating on the ceramics chambers has been observed during machine operation. An air compressor is used to cool these chambers due to concerns of overheating during top-up operation mode. To understand the sources of the heating, a series of experiments are performed with various beam currents and bunch filling patterns. The study shows that the heating is mainly caused by the narrow-band impedances of the ceramic chambers and their adjacent vacuum components.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB036

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paper received ※ 22 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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MOPRB057

An Approach to Alleviating Heavy Beam Loading Effect on the Synchrotron Machine Through the Existed Low Level RF Feedback System

cavity, feedback, beam-loading, simulation

697

L.-H. Chang, F.Y. Chang, M.H. Chang, S.W. Chang, L.J. Chen, F.-T. Chung, Y.T. Li, M.-C. Lin, Z.K. Liu, C.H. Lo, Ch. Wang, M.-S. Yeh, T.-C. Yu
NSRRC, Hsinchu, Taiwan

To pursue the highest brightness and intensity of the synchrotron light, the synchrotron machines are pushed to operate with as high as possible of the beam current. To suppress the heavy beam loading effects, the direct RF feedback is currently widely used. This paper provides an another approach to alleviating the heavy beam loading effects on machine operation. Different from the direct RF feedback technique, this approach need not add additional feedback loop to the existed RF feedback system. Applying a proper angle rotation to the I-Q error signals of the cavity voltage, before entering the existed feedback loop, is the only action required in this approach. The paper will explain the working mechanism and investigate the behaviour of this approach, through an example case, with numerical simulation.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB057

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paper received ※ 16 April 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019

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MOPTS063

Design and Low Power Test of a Prototype HOM LINAC

DTL, HOM, cavity, linac

1001

L. Lu, T. He, C.C. Xing, L. Yang
IMP/CAS, Lanzhou, People’s Republic of China
L. Yang
University of Chinese Academy of Sciences, Beijing, People’s Republic of China

A 325MHz HOM (higher order mode) type linac was proposed and studied for proton or heavy ion acceleration in medium energy region. The cavity was finished the fabrication already by using copper and aluminum material. We will report results of low power test of the HOM linac in this paper.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPTS063

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paper received ※ 29 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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MOPTS089

Transverse Beam Dynamics Studies With High Intensity LHC Beams in the SPS

injection, octupole, emittance, electron

1062

M. Carlà, H. Bartosik, M.S. Beck, L.R. Carver, V. Kain, G. Kotzian, K.S.B. Li, G. Rumolo, C. Zannini
CERN, Geneva, Switzerland

In order to reach the target beam parameters of the LHC injectors upgrade (LIU), about twice the presently operational intensity of LHC type beams has to be achieved. Although the planned upgrade of the main RF system will occur during the long shutdown, a series of measurements have been performed to assess the beam dynamics challenges with these very high intensity beams on the long SPS injection plateau. Bunch-by-bunch transverse emittance blow-up measurements suggested the presence of electron-cloud. After a period of running with the high intensity beam for a couple of days, a clear improvement of beam quality was observed which is attributed to scrubbing. In addition, a horizontal headtail instability is encountered for the usual operational settings of chromaticity and transverse damper. The stability limit as a function of chromaticity and Landau octupole settings has been explored and will be discussed, together with possible sources of the instability and mitigation strategies.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPTS089

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paper received ※ 06 May 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019

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TUZZPLS2

Beam Dynamics, Injection and Impedance Studies for the Proposed Single Pulsed Nonlinear Injection Kicker at the Australian Synchrotron

injection, kicker, synchrotron, storage-ring

1219

R. Auchettl, R.T. Dowd, Y.E. Tan
AS - ANSTO, Clayton, Australia

The Australian Synchrotron are currently investigating the use of a single pulsed nonlinear injection kicker (NLK) to free floor space within the ring for future beamline development. The NLK has a zero and flat magnetic field at the stored beam to leave the stored beam undisturbed but has a maximum field off-axis where the injected beam is located. After the kick, the injected beam is stored. While NLKs have been prototyped at many facilities around the world, injection efficiency and heat loading have been the main impediment to deployment of the NLK. The wakefields that pass through the ceramic chamber aperture can cause severe heat loading and impedance. Despite achieving impressive injection efficiencies, a previous prototype at BESSY II * showed that strong interactions of the stored beam resulted in high heat load causing the thin 5µm Titanium coated ceramic chamber to reach temperatures > 500 °C and fail. To avoid beam induced heat loads, this paper presents studies of the wake impedance and thermal behaviour for our proposed NLK design. Injection simulations and future considerations for installation and operation at the Australian Synchrotron will be discussed.
* T. Atkinson et al., "Development of a non-linear kicker system to facilitate a new injection scheme for the Bessy II storage ring", in Proc. IPAC’11, 2011, THPO024, pp. 3394-3396.

Slides TUZZPLS2 [1.588 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUZZPLS2

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paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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TUPMP044

Special Aluminum Gasket Sealing of Non-circular Profile Flanges for the Accelerator UHV Systems

vacuum, photon, experiment, emittance

1347

G.Y. Hsiung
NSRRC, Hsinchu, Taiwan

Most of the beam ducts for the accelerators are not regularly the circular profile. Unfortunately, the conflat (CF-) flanges and the gaskets with non-circular profile were not commercially available. Besides, additional RF-contact bridges between the flanges must be built in for mitigating the impedance from the flange-gaps. In this presentation, various types of the aluminum (Al-) gaskets designed for the non-circular profile Al-flanges for the accelerator ultrahigh vacuum (UHV) systems are introduced. The surface of the Al-flange is flat to accommodate the special Al-gasket with knife edges for the sealing. Both the flange and gasket are manufactured by the oil-free Ethanol-CNC-machining process that any non-circular profile, e.g. rectangular, race-track, key-hole, etc., flanges can be precisely produced. The inner diameters of the gasket just suits those of the flanges that the impedance from the gap is significantly reduced. The flanges and gaskets after oil-free machining can be assembled immediately without any chemical cleaning. The experimental results for the as-mentioned non-circular profile Al-flanges reveal the UHV quality at pressure < 20 nPa after vacuum baking.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPMP044

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paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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TUPGW015

Petra III Operation and Studies 2018

operation, vacuum, undulator, radiation

1419

M. Bieler, I.V. Agapov, Y.-C. Chae, J. Keil, G.K. Sahoo, R. Wanzenberg
DESY, Hamburg, Germany

At DESY the Synchrotron Light Source PETRA III offers scientists outstanding opportunities for experiments with hard X-rays of exceptionally high brilliance since 2009. This paper describes the operational schedule, the operational statistics and the most important beam studies done at PETRA III in 2018.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW015

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paper received ※ 26 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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TUPGW082

Impedance of the Flange Joints With the RF Contact Spring in NSLS-II

storage-ring, vacuum, cavity, damping

1597

A. Blednykh, B. Bacha, G. Bassi, C. Hetzel, B.N. Kosciuk, T.V. Shaftan, V.V. Smaluk, G.M. Wang
BNL, Upton, Long Island, New York, USA

Funding: This work was supported by Department of Energy Contract No. DE-SC0012704
Since the beginning of the NSLS-II commissioning, temperature of the vacuum components has been moni-tored by the Resistance Temperature Detectors located predominantly outside of the vacuum enclosure and at-tached to the chamber body. Temperature map helps us to control overheating of the vacuum components around the ring especially during the current ramp-up. The average current of 475mA has been achieved with two main 500MHz RF cavities and w/o harmonic cavities. Effect of the RF shielded flanges on local heat and on the longitu-dinal beam dynamics is discussed in details.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW082

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paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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TUPGW092

Working Impedance Model and Its Effect on the Intensity Limitation of Petra-IV Storage Ring

cavity, feedback, emittance, storage-ring

1623

Y.-C. Chae
DESY, Hamburg, Germany

We made sufficient progress in modeling the imped-ance of the PETRA-IV storage ring. The result was ap-plied to estimate the impedance-based single and multi-bunch intensity limit. Due to the extremely small emit-tance of the beam the intrabeam scattering (IBS) effects will be significant unless they are reduced by bunch lengthening. The 3rd harmonic cavity was proposed to dilute the bunch density which resulted in the small syn-chrotron frequency with a large spread. Because of the complexity introduced by impedance and harmonic cavity we used broadband impedance up to 200 GHz to compute the parameters such as bunch length and energy spread at different currents. We found that the microwave instability started very early in current less than 0.5 mA. Even if it is small, the prediction by tracking simulation was consistent with another diffraction-limited storage ring (DLSR) when the Keil-Schnell criterion was used to predict one from the other. Then, we present the single-bunch current limit which had included the effect of geometric and resistive wall impedances of the NEG-coated chamber. Finally, we present the emittance and lifetime which can be realistically achieved in the ring with the above collective effects included.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW092

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paper received ※ 14 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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TUPGW099

Superconducting Crab Cavity Options for Short X-Ray Pulse Generation in SPEAR3

cavity, sextupole, GUI, HOM

1647

F. Toufexis, V.A. Dolgashev, X. Huang, Z. Li
SLAC, Menlo Park, California, USA

Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515.
We are exploring methods to generate short X-ray pulses in SPEAR3 on the order of 1 ps to enable studying ultrafast processes in materials. We are developing a 2-frequency crab cavity scheme with two sets of crab cavities* at the 6th and 6.5th harmonics of the 476 MHz ring RF frequency. In previous work we studied a normal conducting crab cavity for SPEAR3**. In this work we explored two superconducting cavity options: a traditional elliptical cavity and the Quasi-waveguide Resonator***. We found that the Quasi-waveguide Resonator cannot meet our field uniformity specifications due to higher order multipole fields. We then optimized a traditional elliptical cavity with the input, Lower Order Modes, and Higher Order Modes couplers following the Argonne Advanced Photon Source design.
* A. Zholents, et al, Nucl. Instrum. Methods Phys. Res., Sect. A, Vol. 425 (1999), p. 385.
** Z. Li, et al, Proceedings of IPAC17.
*** A. Lunin, et al, Proceedings of HOMSC14.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW099

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paper received ※ 11 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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TUPGW107

Overview of Collective Effects in SLS 2.0

cavity, operation, simulation, damping

1658

M.M. Dehler, M. Aiba, A. Citterio, L. Stingelin
PSI, Villigen PSI, Switzerland

At the end of 2017, the conceptual design for an upgrade of the Swiss Light Source was finished, promising a 40 fold smaller emittance and a corresponding increase of the spectral brightness from the current value. From the point of view of collective effects, the main changes in the new design are a reduced chamber size, fully coated with NEG, and operation at small and negative momentum compaction with low synchrotron frequency. We give an overview of the latest results for the ring. Most critical is the threshold for the longitudinal single bunch instability. Taking into account the combined effect of wake impedances and CSR, we have to rely on bunch stretching by a higher harmonic system to achieve stable operation at nominal current.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW107

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paper received ※ 14 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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TUPGW108

Characterization of NEG Coatings for SLS 2.0

GUI, resonance, coupling, vacuum

1662

M.M. Dehler, A. Citterio
PSI, Villigen PSI, Switzerland
S. Alberti, J.P. Hogge
SPC-EPFL, Lausanne, Switzerland
M. Hahn, H.P. Marques
ESRF, Grenoble, France
X.Y. Liu
USTC/NSRL, Hefei, Anhui, People’s Republic of China

To limit desorption and ameliorate pumping of the narrow 20 mm aperture vacuum chamber of SLS2.0, it is planned to fully coat it with nonevaporable getter (NEG) material. NEG coating can be produced with different structural characteristics, from dense films to columnar growth, with corresponding distinct electrical properties affecting the machine impedance and the instability threshold of the accelerator. In order to evaluate and characterize the coating process for geometries similar to the SLS chamber, we measured the resonance properties of coated and uncoated shorted waveguide pieces. First tests were done with standard X band waveguides at 12 and 7 GHz. Test setups using elliptical cross sections are in preparation, also for higher frequencies allowing the characterization of thin NEG layers. The final goal is to have a standardized process to test of samples coated by external producers. We describe the setups and first results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW108

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paper received ※ 10 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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TUPGW109

Conceptual Design of Vacuum Chamber for SPS-II Storage Ring

vacuum, storage-ring, photon, emittance

1666

T. Phimsen, S. Chaichuay, N. Juntong, P. Klysubun, S. Prawanta, P. Sudmuang, P. Sunwong
SLRI, Nakhon Ratchasima, Thailand
R. Deepan, A. Khamkham
Suranaree University of Technology, Nakhon Ratchasima, Thailand

The SPS-II is a 3 GeV ultralow emittance light source which is now under studied and designed by Thailand Synchrotron Light Research Institute (SLRI). The SPS-II storage ring is based on Double-Triple Bend Achromat (DTBA) cell with a circumference of 321.3 m aiming for horizontal emittance of less than 1 nm-rad. The compact lattice leaves narrow space for vacuum components. The small gap between poles of the magnets requires narrow vacuum chambers and limits the conductance of the chambers. The chambers will be made by stainless steel with a thickness of 1.5 mm. the cross section of beam duct is 40 mm × 16 mm elliptical shape. The bending chamber is designed as a long triangular chamber such that photon absorber can be installed as far from the light source as possible to lower the power density of the heat load. The overview of designed vacuum system for the SPS-II is presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPGW109

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paper received ※ 14 May 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019

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TUPRB101

Damping Trapped Modes in an in-Vacuum Undulator at a Synchrotron Radiation Light Source

simulation, vacuum, damping, HOM

1895

K. Tian, Z. Li, A. Ringwall, J.J. Sebek
SLAC, Menlo Park, California, USA

Funding: Work supported by US Department of Energy Contract DE-AC03-76SF00515.
In this paper, we report the efforts in solving the problem of coupled-bunch instabilities caused by an in-vacuum undulator in the SPEAR3 storage ring. After exploring several approaches to reduce the strength of the trapped modes, we found that ferrite dampers were the most effective and simplest way for mode damping in our SPEAR3 in-vacuum undulator. The results of the first RF cold measurement on an in-vacuum undulator equipped with these ferrite dampers agree well with numerical simulations.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPRB101

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paper received ※ 13 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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TUPTS034

Development of Low Inductance Circuit for Radially Symmetric Circuit

experiment, kicker, high-voltage, operation

2013

T. Takayanagi, K. Horino, T. Ueno
JAEA/J-PARC, Tokai-mura, Japan

Radiation symmetric type circuits using semiconductors of SIC-MOSFETs, one of next generation semiconductors, are composed of circuits in which many semiconductor switches are multiplexed in series and in parallel. Since the lengths of all parallel circuits are equal, the output waveform will not be distorted due to timing jitter or level change. This circuit is useful for outputting the waveform of ultrafast short pulse. Therefore, we have developed a circuit that achieves further low inductance by making the power transmission circuit into a double circular ring structure equal to the coaxial shape. Compare the inductance value obtained from the structure and the output waveform. In addition, we compare the calculation and the actual measurement in the actual test and present the verification result of the developed circular ring structure.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS034

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paper received ※ 01 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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WEYPLS1

Building the Impedance Model of a Real Machine

simulation, wakefield, coupling, cavity

2249

B. Salvant, D. Amorim, S.A. Antipov, S. Arsenyev, M.S. Beck, N. Biancacci, O.S. Brüning, J.V. Campelo, E. Carideo, F. Caspers, A. Farricker, A. Grudiev, T. Kaltenbacher, E. Koukovini-Platia, P. Kramer, A. Lasheen, M. Migliorati, N. Mounet, E. Métral, N. Nasr Esfahani, S. Persichelli, B.K. Popovic, T.L. Rijoff, G. Rumolo, E.N. Shaposhnikova, V.G. Vaccaro, C. Vollinger, N. Wang, C. Zannini, B. Zotter
CERN, Geneva, Switzerland
D. Amorim
Grenoble-INP Phelma, Grenoble, France
T. Dalascu
EPFL, Lausanne, Switzerland
M. Migliorati
Sapienza University of Rome, Rome, Italy
R. Nagaoka
SOLEIL, Gif-sur-Yvette, France
V.V. Smaluk
BNL, Upton, Long Island, New York, USA
B. Spataro
INFN/LNF, Frascati, Italy
N. Wang
IHEP, Beijing, People’s Republic of China
S.M. White
ESRF, Grenoble, France

A reliable impedance model of a particle accelerator can be built by combining the beam coupling impedances of all the components. This is a necessary step to be able to evaluate the machine performance limitations, identify the main contributors in case an impedance reduction is required, and study the interaction with other mechanisms such as optics nonlinearities, transverse damper, noise, space charge, electron cloud, beam-beam (in a collider). The main phases to create a realistic impedance model, and verify it experimentally, will be reviewed, highlighting the main challenges. Some examples will be presented revealing the levels of precision of machine impedance models that have been achieved.

Slides WEYPLS1 [5.648 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEYPLS1

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paper received ※ 10 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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WEPMP016

The Design and Preliminary Test of a Stripline Kicker for HALS

kicker, simulation, vacuum, high-voltage

2338

W. Liu, F.L. Shang, L. Shang, W.B. Song, Z.B. Sun
USTC/NSRL, Hefei, Anhui, People’s Republic of China

Stripline kicker is an important components of both on-axis longitudinal accumulation and on-axis swap out injection schemes in HALS (Hefei Advanced Light Source). After more than one year of R&D, construction of the first prototype is completed. The kicker performance is simulated by CST. The results show that in the range of 0~1GHz, on differential mode, S11 is less than - 23.7dB. In order to facilitate installation, the extension part and PTFE bracket were designed. The assembly of kicker and feedthrough has been tested with pulse generator and network analyser.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPMP016

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paper received ※ 25 April 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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WEPMP018

A Novel Non-Linear Strip-Line Kicker Driven by Fast Pulser in Common Mode

kicker, injection, dynamic-aperture, multipole

2345

J. Chen, Z. Duan, L. Huo, Y. Li, H. Shi, G. Wang, L. Wang, N. Wang
IHEP, Beijing, People’s Republic of China

The next generation storage ring-based light sources adopt multi-bend achromat lattices to achieve a low emittance. The dynamic apertures of these machines are usually less than 10 mm so that the traditional pulsed local bump injection is difficult to achieve. Off-axis injection with a pulsed multipole or a non-linear kicker could be a viable solution which requires a moderate dynamic aperture of a few mm. In this paper, a novel non-linear kicker design is presented. Unlike pulsed sextupole or nonlinear kicker magnet, the nonlinear kicker we proposed is a traveling wave kicker with 2 strip-line electrodes driven by a nanosecond-level fast pulser in common mode. The disturbance to the stored beam is minimal since the perturbation is limited to the target bunch alone.
Work support by NSFC(11475200 and 11675194).

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPMP018

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paper received ※ 30 April 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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WEPMP051

Impedance Study of a New Septum Chamber of SPEAR3

septum, simulation, vacuum, storage-ring

2447

K. Tian, J. Langton, J.J. Sebek
SLAC, Menlo Park, California, USA

Funding: Work supported by US Department of Energy Contract DE-AC03-76SF00515.
A new Septum magnet and chamber has been designed for the storage ring as a part of the accelerator improvement plan for operating a lower emittance lattice in SPEAR3. Therefore it is necessary to analyze the impedance effects on the beam from the new Septum chamber. Due to the complex design at the downstream transition of the Septum chamber, the longitudinal impedance is particular of concern. In this paper, we will present numerical simulation results for this particular component as well as the general analysis for the impedance effects of the whole chamber.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPMP051

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paper received ※ 14 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

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WEPGW075

Coupling Impedance Studies of the Current Transformers at ALBA

resonance, cavity, simulation, factory

2647

T.F.G. Günzel, U. Iriso, A.A. Nosych
ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain

ALBA is equipped with two different current transformers (FCT and DCCT), and a third one (ICT) is now in design stage to be installed in 2019. A comparative study of the different currents transformers was carried out in order to characterize their contribution to longitudinal and transverse impedance. The gap in the vacuum chamber of the current transformers was varied in order to study its effect on the heat deposited by the beam in the corresponding device and on the resonance in the longitudinal impedance spectrum. The simulation results are compared to the experience with the existing current transformers in operation.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPGW075

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paper received ※ 14 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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WEPRB050

Multipacting Studies of the Coaxial Coupler for BNCT DTL

multipactoring, simulation, DTL, neutron

2921

M.X. Fan, A.H. Li, B. Li, J. Peng, P.H. Qu, A.X. Wang, Y. Wang, X.L. Xiaolei
IHEP CSNS, Guangdong Province, People’s Republic of China
Q. Chen, S. Fu, H.C. Liu
IHEP, Beijing, People’s Republic of China
X.L. Wu
DNSC, Dongguan, People’s Republic of China

Funding: Youth Innovation Promotion Association of CAS (2015011) Program for GuangDong Introducting Innovative and Enterpreneurial Teams (2017ZT07S225)
Multipacting is a phenomenon in which electrons grow sharply under certain conditions in a RF structure. It may lead to the breakdown or even damage to the equipment. Therefore, it is very important to calculate the Multipact-ing range in the RF equipment design. Since the phe-nomenon is too complicated to use the formula to fully predict it, numerical simulation is employed. There are many computer codes (such as Track3P, MultiPac, CST PS, etc.) used to simulate the phenomenon, but most of them are not commercial. In this paper, theories used in coaxial line for predicting multipacting are introduced; the CST PS is chosen to simulate the multipacting of coaxial coupler for BNCT DTL; finally, methods of sup-pressing multipacting are discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB050

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paper received ※ 11 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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WEPRB056

Design Study of 325MHz RF Power Coupler for Superconducting Cavity

cavity, superconducting-cavity, resonance, simulation

2937

J.Y. Yoon, H.J. Cha, S.W. Jang, E.-S. Kim, K.R. Kim, C.S. Park, S.H. Park
KUS, Sejong, Republic of Korea
J. Bahng
Korea University Sejong Campus, Sejong, Republic of Korea
K.R. Kim
PAL, Pohang, Kyungbuk, Republic of Korea

We present the design study of the RF input power coupler for 325 MHz superconducting cavities. The power coupler, based on a conventional coaxial transmission line, provides RF powers to the cavity up to 12kW in CW mode. The thermal interceptors are considered as 4.5 K and 40 K or 4.5 K and 77 K corresponding to the usage of liquid Helium only or both liquid Helium and Nitrogen for cryogenic temperature to reduce the thermal load. The transition box (T-box), which is assembled with power coupler, is designed and applied for impedance matching and inner conductor cooling.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB056

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paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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WEPRB066

Utilizing the High Shunt Impedance TM020-Mode Cavity in the Double RF Systems for the Storage Ring of the Thailand New Light Source

cavity, storage-ring, coupling, damping

2972

N. Juntong, T. Phimsen
SLRI, Nakhon Ratchasima, Thailand
N. Chulakham, S. Malichan
Udon Thani Rajabhat University, Udon Thani, Thailand

The utilization of the TM020-mode cavity for the storage ring based light source was pioneered by SPring-8 with its high quality factor and hence its high shunt impedance. KEK-LS has also studied the possibility of using this type of cavity for their storage ring. The TM020-mode cavity has larger transverse dimension compared to the traditional TM010-mode cavity, but with its higher shunt impedance it can be designed to fit in the new low emittance storage ring regardless. The new storage ring based light source project in Thailand aims to optimum the low emittance beam in nano-meters region with the energy of 3 GeV. The TM020-mode cavity was considered as the main cavity and the harmonic cavity for the storage ring. They have been designed to have their pipe aperture fits the storage ring beam ducts. The main cavity has a high shunt impedance of 8.3 Mega Ohms with the 51,000 unloaded quality factor. The harmonic cavity has a high shunt impedance and an unloaded quality factor of 2.45 Mega Ohms and 36,000, respectively. The damping mechanism of the parasitic modes and the tuning mechanism of the operating mode of these cavities were also studied. There will be four main cavities and six harmonic cavities in the new storage ring. Detailed design and study of these cavities will be presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB066

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paper received ※ 29 April 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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WEPRB068

Ka-Band Linearizer Studies for a Compact Light Source

wakefield, klystron, FEL, flattop

2976

A. Castilla, G. Burt, W.L. Millar
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
A. Latina, X. Liu, W.L. Millar, X.W. Wu, W. Wuensch
CERN, Geneva, Switzerland

Funding: This project has received funding from the European Union’s Horizon2020 research and innovation programme under grant agreement No 777431.
The CompactLight project is currently developing the design of a next generation hard X-ray FEL facility, based on high-gradient X-band (12 GHz) structures, bright electron photo-injectors, and compact short period undulators. However, to improve the brightness limitations due to the non-linear energy spread of the electron bunches, a K-band (36 GHz) linearizer is being considered to provide a harmonic compensation during the bunch compression. In this paper, we analyze the feasibility of such linearizer.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB068

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paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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WEPRB073

CW Room Temperature Accelerating Structures

operation, electron, radiation, SRF

2990

S.P. Antipov, P.V. Avrakhov, E. Gomez, S.V. Kuzikov
Euclid TechLabs, LLC, Solon, Ohio, USA
A.A. Vikharev
IAP/RAS, Nizhny Novgorod, Russia

To this day CW linear electron accelerators were based only on expensive and bulky (embedded in a cryostat) superconducting accelerating structures. CW regime can in principle be realized with normal conducting structures provided the shunt impedance is high. Such structures can be designed using dielectrics (ultra-pure ceramics in C-band and diamond in mm-waves) with ultra-low loss tangent (~10-6). The use of dielectrics allows to concentrate the electromagnetic energy density in the dielectric region and thus minimize fields and ohmic loss on metallic walls. The thermal loss in dielectric can be relatively low given the loss tangent is small. We report here the design of structures with shunt impedance on the order of 10⁴ MOhm/m, which is several orders of magnitude higher than shut impedance in copper structures in GHz and THz range. High shunt impedance makes it possible to accelerate electrons to 1 MeV using kW-level CW RF sources like magnetrons in C-band and gyrotrons in THz range. Such CW accelerators will find applications in sterilization, food irradiation, industrial radiography and cargo inspection.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB073

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paper received ※ 21 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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WEPRB080

Optimization of RF Cavities Using MOGA for ALS-U

cavity, simulation, controls, gun

3007

H.Q. Feng, K.M. Baptiste, D. Li, T.H. Luo
LBNL, Berkeley, California, USA
H.Q. Feng, W.-H. Huang, Z.N. Liu, C.-X. Tang
TUB, Beijing, People’s Republic of China

Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231
A multi-objective genetic algorithm-based optimiza-tion process has been applied to optimize the RF design of a 500 MHz main cavity and a 1.5 GHz Higher Harmon-ic Cavity (HHC) for the Advanced Light Source upgrade (ALS-U) in Lawrence Berkeley National Laboratory (LBNL). For the main cavity, a significant improvement, compared with the existing ALS cavity, has been achieved in cavity shunt impedance and power loss den-sity simultaneously. The field strengths and distribution of the optimized structure are analysed for further re-search. For the HHC, a cavity with low R/Q has been pre-liminary designed to mitigate the beam instability. This study also serves as an example of how a genetic algo-rithm can be used for optimizing RF cavities.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB080

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paper received ※ 16 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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WEPRB081

Design Study on Higher Harmonic Cavity for ALS-U

cavity, higher-order-mode, simulation, wakefield

3011

H.Q. Feng, K.M. Baptiste, S. De Santis, D. Li, T.H. Luo
LBNL, Berkeley, California, USA
H.Q. Feng, W.-H. Huang, Z.N. Liu, C.-X. Tang
TUB, Beijing, People’s Republic of China

Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231
The ALS upgrade (ALS-U) to a diffraction-limited light source [1] depends on the ability to lengthen the stored bunches to limit the emittance growth and increase the beam life time. Higher harmonic cavities (HHCs), also known as Landau cavities, have been proposed to in-crease beam lifetime and Landau damping by lengthen-ing the bunch. We present an optimized 1.5 GHz normal conducting HHC design for the ALS-U with a supercon-ducting-like geometry using multi-objective genetic algorithm (MOGA) for lower R/Q. The optimization goal is to reach the required shunt impedance while maintain-ing a relatively high Q value of the cavities. To minimize the coupled bunch instabilities, higher-order mode (HOM) of the HHC as well as corresponding impedance are explored and characterized.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB081

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paper received ※ 16 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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WEPRB105

Design of an X-Band Constant Impedance LINAC for Compact Light Project

simulation, linac, quadrupole, framework

3055

J.M. Arnesano, A. Mostacci, L. Palumbo
Sapienza University of Rome, Rome, Italy
M. Diomede, M. Marongiu
INFN/LNF, Frascati, Italy
L. Ficcadenti
INFN-Roma, Roma, Italy

Within the framework of Horizon 2020 project, Compact Light, in order to provide a high performance, high-gradient X-band technology, for the new generation of hard X-ray FEL, a travelling wave (TW) Linac, working on 2pi/3 mode at 11.9952 GHz, fed by two types of asymmetrically couplers, has been designed. The design was performed using CST Microwave Studio frequency domain solver. First, simulations have been conduct in order to obtain the best trade-off between single cell’s parameters, varying iris aperture. Then, the both couplers, with and without pumping port, has been tuned to avoid reflections at the input port. Finally, the entire structure, with 5 cells, was simulated. The main structure parameters will be present and we will also show and discuss the acceleranting gradient obtained vary with linac lenght and input power.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB105

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paper received ※ 15 May 2019 paper accepted ※ 24 May 2019 issue date ※ 21 June 2019

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WEPRB107

The New 1-18 MHz Wideband RF System for the CERN PS Booster

cavity, vacuum, electronics, electron

3063

M.M. Paoluzzi, L. Arnaudon, V. Bretin, Y. Cuvet, J. Daricou, S. Energico, M. Haase, A.J. Jones, D. Landré, C. Rossi
CERN, Meyrin, Switzerland
C. Ohmori
KEK/JAEA, Ibaraki-Ken, Japan

The LHC Injector Upgrade (LIU) project at CERN prepares the injectors to meet the requirements of the High Luminosity LHC. For protons, it includes the new Linac4, PS Booster (PSB), PS and SPS. Among the major changes concerning the PSB, the extraction energy increase from 1.4 GeV to 2 GeV and the higher beam intensity, made possible by the Linac4 together with the new charge exchange injection system into the PSB (2·10¹³ protons) strongly affect the RF system requirements. To deal with this more demanding beam operation, a new RF system was designed. It is based on modern magnetic alloy loaded cavities driven by solid-state amplifiers. Its wideband frequency response (1 MHz to 18 MHz) covers all the required frequency schemes. This new RF system has been produced in 2017 and 2018; installation is planned during 2019, the first year of Long Shutdown 2 (LS2) and commissioning foreseen in 2020. Most of the production and testing was outsourced to industry; parts acceptance, cavities assembly and pre-testing was done in-house. A quality assurance plan was established to achieve the required high reliability. This paper describes the procurement, production and testing strategies and methodologies. It also reports the achieved results, system performances and relevant statistics.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB107

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paper received ※ 26 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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WEPTS012

RF Design Studies of a 1.3 GHz Normal Conducting CW Buncher for European X-FEL

multipactoring, simulation, coupling, cavity

3109

S. Lal, Y. Chen, H.J. Qian, H. Shaker, G. Shu, F. Stephan
DESY Zeuthen, Zeuthen, Germany
V.V. Paramonov
RAS/INR, Moscow, Russia

A CW upgrade of European XFEL is under consideration, and CW electron injector is under R&D at DESY. One of the injector solutions is the LCLS-II like injector based on a normal conducting CW gun and buncher. RF design of a 1.3 GHz normal conducting buncher structure with accelerating voltage of ~ 400 kV, for such a CW injector is carried out at DESY Zeuthen site. The buncher structures with different geometrical shapes and numbers of cells are studied. The designs are optimized to have higher shunt impedance, higher mode separation and lower thermal power density for CW operation. Multipacting analysis and beam dynamics simulations are also presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS012

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paper received ※ 12 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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WEPTS049

Flat-Bottom Instabilities in the CERN SPS

simulation, HOM, feedback, LLRF

3224

M. Schwarz, K. Iliakis, A. Lasheen, G. Papotti, J. Repond, E.N. Shaposhnikova, H. Timko
CERN, Meyrin, Switzerland

At beam intensities of 2.6·10¹¹ protons per bunch, required at SPS injection for the High Luminosity LHC beam, longitudinal instabilities can degrade the beam quality delivered by the SPS, the LHC injector at CERN. In this paper, we concentrate on beam instability at flat bottom. The dependence of the instability threshold on longitudinal emittance and LLRF system settings was measured, to help identify the impedance driving this instability. While reducing the longitudinal emittance reduces the losses at injection, it can drive the beam unstable. The LLRF system of the SPS (partially) compensates beam loading, but also affects the instability. The effect of the different LLRF systems (feedback, feedforward, phase loop and longitudinal damper) and fourth harmonic RF system on the instability was investigated. The measurements are compared with simulations performed with the longitudinal tracking code BLonD.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS049

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paper received ※ 10 May 2019 paper accepted ※ 19 May 2019 issue date ※ 21 June 2019

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WEPTS089

Microbunching Instability Mitigation via Multi-Stage Cancellation

bunching, electron, linac, laser

3321

J. Qiang, B. Li
LBNL, Berkeley, California, USA

Funding: This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and used computer resources at the National Energy Research Scientific Computing Center.
The microbunching instability driven by beam collective effects in the linear accelerator of a free electron laser (FEL) facility can significantly degrade electron beam quality and FEL performance. Understanding and control of the instability is a priority for the design of modern high-brightness electron accelerators. In this paper, we study an instability cancellation phenomenon due to 180 degree phase slippage of the current modulations between different amplification stages. A case study of using a nonisochronous dogleg section in a double compression scheme to cancel the current modulation is illustrated.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS089

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paper received ※ 07 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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WEPTS101

A General Comparison on Impedance Theory and CST Simulation of Discontinuities

simulation, vacuum, coupling, storage-ring

3352

N. Khosravi, E. Ahmadi, M. Akhyani, S. Dastan, A.M. Mash’al
ILSF, Tehran, Iran
H. Karimi
Isfahan University of Technology, Isfahan, Iran

Inhomogeneity of vacuum chamber components is the main source of coupling impedance. Nowadays, wake potential is mostly predictable by 3D codes. Analytical prediction of impedance theories can be helpful as a side solution. On the other hand, some asymmetries in the geometry of components might make troubles and lead to imprecise numerical results in 3D simulations. Analytical approximation of discontinuities, holes, and grooves can give us an estimation of expected results and can be used as a benchmark in the case that we do not have any experimental data. To clarify the validity of theoretical expressions, general discontinuities are simulated in CST. The comparison of final results is presented here. At last, resistive wall impedance and some general discontinuities of components at ILSF storage ring are compared from the theoretical and simulation point of view.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS101

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paper received ※ 01 May 2019 paper accepted ※ 24 May 2019 issue date ※ 21 June 2019

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THPGW033

Numerical Study of Photonic-Crystal-Based Dielectric Accelerators

GUI, photon, acceleration, electron

3653

G. Torrisi, L. Celona, S. Gammino, D. Mascali, G. Sorbello
INFN/LNS, Catania, Italy
C. De Angelis, A. Locatelli
University of Brescia, Brescia, Italy
G.S. Mauro
INFN/LNL, Legnaro (PD), Italy
G. Sorbello
University of Catania, Catania, Italy

All-dielectric electromagnetic band gap (EBG) waveguides structures promise significant improvement of accelerating gradient of laser-driven acceleration with the potential to miniaturize the accelerator itself. In this work we study photonic crystal structures designed for acceleration of relativistic electrons. We explore the performance of the all-dielectric EBG accelerating waveguide structures thanks to full wave electromagnetic simulations of couplers and accelerating waveguides. The characteristic interaction impedance, accelerating gradient and all the key parameters that are typically used to characterize linear accelerators are evaluated and used to compare the properties of the accelerating mode field distribution in different geometries.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPGW033

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paper received ※ 30 April 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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THPRB026

A 300 mm Long Prototype Strip-Line Kicker for the Heps Injection System

kicker, vacuum, injection, simulation

3864

L. Wang, J. Chen, L. Huo, P. Liu, H. Shi, X.L. Shi, G. Wang, N. Wang
IHEP, Beijing, People’s Republic of China

In the High Energy Photon Source (HEPS), the dynamic aperture of machine is not large enough for off-axis injec-tion for its baseline 7BA lattice design. So, a group of superfast kickers with about 12 ns pulse bottom width are needed for on-axis swap out injection scheme. The design about a couple sets of 300 mm long strip-line kickers is presented. Five kickers as a module are placed in a stain-less steel vacuum vessel to solve the problem of longitu-dinal space restriction in injection area. So far, the proto-type development of strip-line kicker was completed. The results of time-domain reflectometer (TDR) test and high voltage pulse test show that the strip-line kicker can meet the requirement of the HEPS.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB026

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paper received ※ 06 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

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THPRB049

MODELING AND SIMULATION FOR MULTI-FEEDING CAVITY WITHOUT BEAM LOADING

cavity, electron, simulation, beam-loading

3921

K. Liu, Q. Gu, L. Li, Ch. Wang, M.H. Zhao
SINAP, Shanghai, People’s Republic of China
Q. Gu
SSRF, Shanghai, People’s Republic of China

The Multi-feeding cavity usually be applied in super-conducting and normal-conducting RF cavity. The differences between multiple input couplers in coupler coefficient, incident power and phase will cause the cavity field stabilities can not meet the requirements. For explore the influences of these differences and develop equations for measurement, a multi-feeding LCR transient model was developed. As two-feeding cavity, the VHF photocathode electron gun was model and simulated in this paper.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB049

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paper received ※ 06 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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THPRB054

Design of a Ultrafast Stripline Kicker for Bunch-by-Bunch Feedback

kicker, FEL, feedback, HOM

3931

J. Wang, P. Li, D. Wu, D.X. Xiao, L.G. Yan
CAEP/IAE, Mianyang, Sichuan, People’s Republic of China

Lorentz force detuning and beam loading effect of the rf cavities will induce a slope of the cavity gradient. Combed with the cavity misalignments, transverse position of subsequent bunches will differ from each other. The CAEP THz Free Electron Laser facility(CTFEL) will have a fast transverse bunch-by-bunch feedback system on its test beamline, which is used to correct the beam position differences of individual bunches in the macro-pulses. The time response of the kicker is rigid for the interval of the micro-pulses is 18.5ns and will upgrade to about 2 ns, requiring impedance matching of the kicker with the power source and transmission system in a high bandwidth. Also, the electromagnetic field must reach the requirements of the beam parameters. In this paper, the structure design and the optimization of the geometric parameters of the ultrafast stripline kicker is presented. The characteristic impedance, transmission characteristics, field consistency are analyzed and optimized. And the feedback signal generation scheme for continuous bunch trains was proposed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB054

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paper received ※ 14 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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THPRB075

Transverse Impedance Measurements and Simulations of the LHC Injection Kicker Magnet

simulation, kicker, injection, coupling

3986

V. Vlachodimitropoulos, M.J. Barnes, A. Chmielinska, L. Ducimetière
CERN, Geneva, Switzerland
A. Chmielinska
EPFL, Lausanne, Switzerland

Kicker magnets contribute significantly to the total impedance budget of many accelerators. Of particular interest, from a beam stability point of view, is the transverse beam coupling impedance (TBCI) that is used to determine intensity limitations of a machine. Until recently, no conclusive TBCI data for the Large Hadron Collider (LHC) injection kicker magnets (MKIs) was available. However, in view of the upgrade of the MKIs for the High-Luminosity LHC (HL-LHC) project, the TBCI of the existing design needed to be estimated to be used as reference for an upgraded version. To that end, electromagnetic simulations were carried out to determine the dipolar and quadrupolar components of the TBCI in the two transverse planes. To validate the simulations, test bench measurements were performed using standard RF measurement techniques. In the present work, the results from TBCI simulations and measurements are reported and compared. Detailed descriptions of the methods and techniques used as well as the realization of the experimental set-up are also given.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB075

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paper received ※ 14 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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THPRB092

Reduction of Beam Induced RF-Heating in the Horizontal Stripline Kicker at the TPS

kicker, storage-ring, feedback, damping

4035

P.J. Chou, C.K. Chan, C.-C. Chang, K.T. Hsu, K.H. Hu, C.K. Kuan, I.C. Sheng
NSRRC, Hsinchu, Taiwan

In preparation for 500 mA operation at the Taiwan Pho-ton Source (TPS), we redesigned the horizontal stripline kicker for the beam feedback system to gain a smaller loss factor with higher shunt impedance. We introduced ground fenders (see Fig. 1) to this new design which resulted in the reduction of the loss factor and substantial increase of the kicker shunt impedance. The transverse profile of the kicker electrodes was matched to the race-track beam pipe in the straight sections to minimize broadband impedance. The ground fenders can reduce the leakage of image currents through the gaps between the two strip line electrodes and also help to achieve a better impedance matching for the TEM modes in the transmission lines formed by the stripline electrodes and beam pipe in the kicker. The RF design and analysis of trapped resonant modes in the kicker were simulated by the 3-D electromagnetic code GdfidL [1]. Results of the RF design and analysis of trapped resonant modes will be discussed together with analytical estimates of coupled bunch instabilities at a beam current of 500 mA.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPRB092

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paper received ※ 17 April 2019 paper accepted ※ 19 May 2019 issue date ※ 21 June 2019

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THPTS013

Further Designs of HOM Couplers for Superconducting 400 MHz RF Cavities

cavity, HOM, simulation, proton

4132

N.F. Petry, M. Busch, K. Kümpel, O. Meusel, H. Podlech
IAP, Frankfurt am Main, Germany

The Future Circular Collider (FCC) is one possible future successor of the Large Hadron Collider (LHC) at CERN. The proton-proton collider center-of-mass collision energy is set to 100 TeV with a beam current of 0.5 A. To achieve this energy a stable acceleration is critical and therefore higher order modes (HOM) need to be damped. HOM dampers, further characterized as couplers, need to fulfill several criteria to be efficient. As a first property the couplers should assure a longitudinal impedance of higher order modes of below 10 kW. Furthermore, the loaded Q-factor should be below 1000 and the corresponding R/Q value should be in the range of 10 Ω. Besides the Hook-type and Probe-type HOM coupler two additional designs were simulated. The recent results of the different couplers attached to a superconducting 400 MHz RF cavity will be presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPTS013

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paper received ※ 09 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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THPTS039

DESIGN OF A COMPACT VARIABLE X-BAND RF POWER SPLITTER

GUI, klystron, electron, network

4194

F. Liu, H.B. Chen, J.Y. Liu, Z.N. Liu, J. Shi, H. Zha
TUB, Beijing, People’s Republic of China

This paper presents a design of a compact variable X-band RF power splitter. The RF power splitter includes one input port and two output ports, and the power divi-sion ratio can be adjusted by changing the position of a short circuit piston. This system keeps a good match (less than -40 dB) at any power division ratio. An E-bend waveguide structure is selected to make the geometry more compact (11cm in length, 3.5cm in width and 5 cm in height). Special studies was conducted to sustain a low surface electrical field (maximum 65 MV/m at 100 MW input), and large bandwidth (250MHz). This power split-ter is designed for high-power test stand at Tsinghua Uni-versity.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPTS039

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paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

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THPTS065

Analysis on the Thermal Response to Beam Impedance Heating of the Post Ls2 Proton Synchrotron Beam Dump

simulation, proton, site, wakefield

4260

L. Teofili, F. Giordano, I. Lamas, F.-X. Nuiry, G. Romagnoli, B. Salvant
CERN, Geneva, Switzerland
M. Marongiu, M. Migliorati
Sapienza University of Rome, Rome, Italy

The High Luminosity Large Hadron Collider (HL-LHC) and the LIU (LHC-Injection Upgrade) projects at CERN are upgrading the whole CERN accelerators chain, increasing beam brightness and intensity. In this scenario, some critical machine components have to be redesigned and rebuilt. Due to the increase in beam intensity, minimizing the electromagnetic interaction between the beam and the device is a crucial design task. Indeed, these interactions could lead to beam instabilities and excessive thermo-mechanical loadings in the device. In this context, this paper presents an example of multi-physics study to investigate the impedance related thermal effects. The analysis is performed on the conceptual design of the new proton synchrotron (PS) internal dump.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPTS065

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paper received ※ 26 April 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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THPTS095

High Efficiency High Power Resonant Cavity Amplifier For PIP-II

cavity, coupling, network, operation

4335

M.P.J. Gaudreau, D.B. Cope, E.G. Johnson, M.K. Kempkes, R.E. Simpson, N.A. Stuart
Diversified Technologies, Inc., Bedford, Massachusetts, USA

Funding: Work 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 70% efficiency, at 675 watts per transistor at 650 MHz. The patent pending design simplifies solid-state transmitters to create straightforward scaling to 200 kW and higher high power levels. A crucial innovation is the reliable "soft-failure" mode of operation; a failure in one or more of the transistors has negligible performance impact. This design couples the transistor drains directly to the cavity without first transforming to 50 Ohms, avoiding the circulators, cables, and connectors that would normally be required. Under an ongoing SBIR grant from the US Department of Energy, DTI designed the system to accommodate over 96 transistors in each 50 kW cavity, with minimal RF, DC, and cooling connections. By the end of the SBIR, DTI will build and demonstrate a complete 100 kW-class (~200 kW) transmitter by combining four cavity modules to show the expandability of the design to very high power levels, comparable to large VEDs.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPTS095

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paper received ※ 19 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

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