IPAC2021 - Classification: MC5: Beam Dynamics and EM Fields / D04 Beam Coupling Impedance - Theory, Simulations, Measurements, Code Developments

Paper	Title	Page
MOPAB117	Single Bunch Collective Effects in the EBS Storage Ring	425
	L.R. Carver, E. Buratin, N. Carmignani, F. Ewald, L. Hoummi, S.M. Liuzzo, T.P. Perron, B. Roche, S.M. White ESRF, Grenoble, France
	The ESRF storage ring (SR) has been dismantled and replaced by the Extremely Brilliant Source (EBS) which has now been commissioned. Beam based measurements have been performed to characterise the impedance of the new machine and to make a first comparison with predictions. The results from instability threshold scans and tune shift measurements will be presented, as well as bunch length and position variation with current and microwave threshold measurements.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB117
About •	paper received ※ 11 May 2021 paper accepted ※ 31 May 2021 issue date ※ 25 August 2021
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MOPAB211	Beam Coupling Impedances of Ferrite-Loaded Cavities: Calculations and Measurements	696
	S.S. Kurennoy, R.C. McCrady LANL, Los Alamos, New Mexico, USA
	We have developed an efficient method of calculating impedances in cavities with dispersive ferrite dampers. The ferrite dispersive properties in the frequency range of interest are fitted in CST, which allows using both wakefield and lossy eigenmode solvers. A simple test cavity with or without ferrite inserts is explored both numerically and experimentally. The resonance frequencies and beam coupling impedances at cavity resonances are calculated with CST to understand the mode structure. The cavity transverse coupling impedances are also measured on a test stand using a two-wire method. We compare results of impedance calculations and measurements for a few different configurations, with and without ferrites, to ensure a complete understanding of the cavity resonances and their damping with ferrite. These results are important to provide adequate damping of undesired transverse modes in induction-linac cells.
	Poster MOPAB211 [1.105 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB211
About •	paper received ※ 10 May 2021 paper accepted ※ 21 May 2021 issue date ※ 19 August 2021
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TUPAB244	THE WAKEFIELD STUDY OF THE RF-SHIELDED BELLOWS AT THE ILSF STORAGE RING	2015
	N. Khosravi, E. Ahmadi, M. Akhyani ILSF, Tehran, Iran M. Akhyani EPFL, Lausanne, Switzerland A. Khosravi LAPRI, Tehran, Iran
	The corrugated geometry of the bellows made it critical to be shielded with an RF-Shield. Different types of RF shields can be applied to the ILSF vacuum chamber to cover this component’s destructive impedance peaks. Then, the Impedance study and optimization of the RF shields can improve the impedance budget. In this article, two common types of RF shields are simulated in CST software.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB244
About •	paper received ※ 16 May 2021 paper accepted ※ 02 June 2021 issue date ※ 14 August 2021
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TUPAB245	WAKEFIELD AND HEAT LOAD STUDY OF THE GATE VALVES AT ILSF STORAGE RING	2018
	N. Khosravi, E. Ahmadi, M. Akhyani ILSF, Tehran, Iran M. Akhyani EPFL, Lausanne, Switzerland S. Dastan IPM, Tehran, Iran A. Khosravi LAPRI, Tehran, Iran
	As one part of the ILSF storage ring, the rf-shield of the gate valves generates considerable interest in terms of wake impedance and heat-load. Inside the gate valves, there is a vacuity, which causes low frequencies resonances, and it can lead to beam instabilities. Therefore, controlling and eliminating these frequencies will be substantial. A radio frequency rf-shield structure, which conceals this transverse gap of the gate valves, is indispensable for low emittance chambers. This paper analyzes the wake impedance and thermal behavior of a finger-band RF shield in the gate valve.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB245
About •	paper received ※ 16 May 2021 paper accepted ※ 14 June 2021 issue date ※ 13 August 2021
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TUPAB251	Impedance Studies of a Corrugated Pipe for KARA	2039
	S. Maier, M. Brosi, A. Mochihashi, A.-S. Müller, M.J. Nasse, M. Schwarz KIT, Karlsruhe, Germany
	Funding: DFG project 431704792 in the ANR-DFG collaboration project ULTRASYNC and the DFG-funded Doctoral School "Karlsruhe School of Elementary and Astroparticle Physics: Science and Technology". At the KIT storage ring KARA (KArlsruhe Research Accelerator) it is planned to install an impedance manipulation structure in a versatile chamber to study and eventually control the influence of an additional impedance on the beam dynamics and the emitted coherent synchrotron radiation. For this purpose the impedance of a corrugated pipe is under investigation. In this contribution, we present first results of simulations showing the impact of different structure parameters on its impedance and wake potential.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB251
About •	paper received ※ 19 May 2021 paper accepted ※ 17 June 2021 issue date ※ 26 August 2021
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TUPAB252	Minimization of NICA Collider Impedance	2043
	S.A. Melnikov, I.N. Meshkov JINR, Dubna, Moscow Region, Russia K.G. Osipov JINR/VBLHEP, Dubna, Moscow region, Russia
	The paper presents the results of the longitudinal impedance minimization for the beam tube section in the arches of the NICA collider ring, consisting of a pumping pipe, a BPM station, and a bellows assembly, and considers the contribution of the impedance of this section to the ion beam stability in the NICA collider ring. To confirm the efficiency of the optimized design, a BPM prototype was fabricated, and a test bench was built for further laboratory measurements.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB252
About •	paper received ※ 13 May 2021 paper accepted ※ 14 June 2021 issue date ※ 10 August 2021
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TUPAB255	Longitudinal Beam Dynamics and Coherent Synchrotron Radiation at cSTART	2050
	M. Schwarz, E. Bründermann, D. El Khechen, B. Härer, A. Malygin, A.-S. Müller, M.J. Nasse, A.I. Papash, R. Ruprecht, J. Schäfer, M. Schuh, P. Wesolowski KIT, Karlsruhe, Germany
	The compact STorage ring for Accelerator Research and Technology (cSTART) project aims to store electron bunches of LWFA-like beams in a very large momentum acceptance storage ring. The project will be realized at the Karlsruhe Institute of Technology (KIT, Germany). Initially, the Ferninfrarot Linac- Und Test-Experiment (FLUTE), a source of ultra-short bunches, will serve as an injector for cSTART to benchmark and emulate laser-wakefield accelerator-like beams. In a second stage a laser-plasma accelerator will be used as an injector, which is being developed as part of the ATHENA project in collaboration with DESY and Helmholtz Institute Jena (HIJ). With an energy of 50 MeV and damping times of several seconds, the electron beam does not reach equilibrium emittance. Furthermore, the critical frequency of synchrotron radiation is 53 THz and in the same order as the bunch spectrum, which implies that the entire bunch radiates coherently. We perform longitudinal particle tracking simulations to investigate the evolution of the bunch length and spectrum as well as the emitted coherent synchrotron radiation. Finally, different options for the RF system are discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB255
About •	paper received ※ 17 May 2021 paper accepted ※ 21 June 2021 issue date ※ 29 August 2021
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TUPAB256	Investigation of Damping Effects of the Crab Cavity Noise Induced Emittance Growth	2054
	N. Triantafyllou, L.R. Carver, A. Wolski The University of Liverpool, Liverpool, United Kingdom F. Antoniou, H. Bartosik, P. Baudrenghien, X. Buffat, R. Calaga, Y. Papaphilippou, N. Triantafyllou CERN, Meyrin, Switzerland L.R. Carver ESRF, Grenoble, France T. Mastoridis CalPoly, San Luis Obispo, California, USA
	Crab cavities will be installed at the two main interaction points (IP1 and IP5) of the High Luminosity LHC (HL-LHC) in order to minimize the geometric reduction of the luminosity due to the crossing angle. Two prototype crab cavities have been installed into the SPS machine and were tested with a proton beam in 2018, to study the expected emittance growth induced by RF noise. The measured emittance growth was found to be a factor 2-3 lower than predicted from the available analytical and computational models. Damping mechanisms from the transverse impedance, which is not included in the available theories, are studied as a possible explanation for the observed discrepancy.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB256
About •	paper received ※ 18 May 2021 paper accepted ※ 18 June 2021 issue date ※ 23 August 2021
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TUPAB257	Analysis of Multibunch Spectrum for an Uneven Bunch Distribution in a Storage Ring	2058
	R. Li, F. Marhauser JLab, Newport News, Virginia, USA
	Funding: This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. Modern storage-ring designs often require an uneven bunch distribution pattern. An uneven bunch fill pattern can result in complex structures for the beam current spectra. Particularly at high average beam currents, these complex current spectra need to be taken into account in concern of beam-dynamical effects. In this study, we analyze a beam current spectrum for various filling patterns with bunch trains and gaps. The characteristics of the resulting beam current spectra are illustrated and discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB257
About •	paper received ※ 21 June 2021 paper accepted ※ 28 June 2021 issue date ※ 12 August 2021
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TUPAB261	The Ferrite Loaded Cavity Impedance Simulation	2070
	L. Huang, X. Li, S. Wang, S.Y. Xu IHEP, Beijing, People’s Republic of China B. Wu IHEP CSNS, Guangdong Province, People’s Republic of China
	Funding: Work supported by NNSF of China: N0. U1832210 The Rapid Cycling Synchrotron of the China Spallation Neutron Source is a high-intensity proton accelerator, it accumulates the 80 MeV proton beam and accelerates it to 1.6 GeV in 20 ms. The transverse coupling bunch instability is observed in beam commissioning. The source has been investigating from the commissioning. The RF acceleration system consists of eight ferrite-loaded cavities. The impedance is simulated and there is a narrow-band impedance of the ferrite cavity at about 17 MHz
	Poster TUPAB261 [1.145 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB261
About •	paper received ※ 13 May 2021 paper accepted ※ 31 May 2021 issue date ※ 21 August 2021
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TUPAB264	Shielding of CSR Wake in a Drift	2079
	G. Stupakov SLAC, Menlo Park, California, USA
	Funding: Work supported by the Department of Energy, contract DE-AC03-76SF00515. A one-dimensional model of coherent synchrotron radiation (CSR) wakefield developed in Refs. [,] is used in computer codes for the simulation of relativistic electron beams. It includes transient effects at the entrance and exit from a bending magnet of finite length. In the ultra-relativistic limit, v=c, the exit CSR wake decays inversely proportional to the distance from the magnet end. To calculate the total energy loss of the beam one needs to integrate this wake to infinity, but the integral diverges. This means that one has to either drop the assumption of the infinite value of the Lorentz factor or take into account the shielding effect of the metal walls in the vacuum chamber. In practice, the latter effect is often dominant. In this work, we derive formulas for the CSR wake in the drift after an exit from the magnet that incorporates the shielding by two parallel metal plates. They allow computing the energy loss of different particles in the beam. E. L. Saldin, E. A. Schneidmiller, and M. V. Yurkov. NIMA v. 398, p. 373 (1997). ** G. Stupakov and P. Emma. In: Proceedings of 8th EPAC. Paris, France, 2002, p. 1479.
	Poster TUPAB264 [0.661 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB264
About •	paper received ※ 10 May 2021 paper accepted ※ 25 June 2021 issue date ※ 22 August 2021
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TUPAB265	Bunch Lengthening of the HALF Storage Ring in the Presence of Passive Harmonic Cavities	2082
	T.L. He, Z.H. Bai, G.Y. Feng, W. Li, W.W. Li, G. Liu, L. Wang, H. Xu, S.C. Zhang USTC/NSRL, Hefei, Anhui, People’s Republic of China
	A passive 3^rd harmonic RF system, being necessary for the Hefei Advanced Light Facility (HALF) storage ring under design, will be employed to lengthen the bunches for suppressing the intrabeam scattering and improving the beam lifetime. However, the transient beam loading due to the fundamental mode may significantly reduce the bunch lengthening. Since the scale of transient effects is proportional to R/Q, the effects of R/Q on bunch lengthening, in uniform fill pattern with the near-optimum condition fulfilled, are analyzed by multibunches multiparticles tracking simulation. It indicates that the passive superconducting harmonic cavity with a lower R/Q is preferred by HALF.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB265
About •	paper received ※ 16 May 2021 paper accepted ※ 18 June 2021 issue date ※ 20 August 2021
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TUPAB267	Investigation of Beam Impedance and Heat Load in a High Temperature Superconducting Undulator	2089
	D. Astapovych, H. De Gersem, E. Gjonaj TEMF, TU Darmstadt, Darmstadt, Germany T.A. Arndt, E. Bründermann, N. Glamann, A.W. Grau, B. Krasch, A.-S. Müller, R. Nast, D. Saez de Jauregui, A. Will KIT, Eggenstein-Leopoldshafen, Germany
	The use of high temperature superconducting (HTS) materials can enhance the performance of superconducting undulators (SCU), which can later be implemented in free electron laser facilities, synchrotron storage rings and light sources. In particular, the short period < 10 mm undulators with narrow magnetic gap < 4 mm are relevant. One of the promising approaches considers a 10 cm meander-structured HTS tapes stacked one above the other. Then, the HTS tape is wound on the SCU. The idea of this jointless undulator has been proposed by, and is being further developed at KIT. Since minimizing the different sources of heat load is a critical issue for all SCUs, a detailed analysis of the impedance and heat load is required to meet the cryogenic system design. The dominant heat source is anticipated to be the resistive surface loss, which is one of the subjects of this study. Considering the complexity of the HTS tape, the impedance model includes the geometrical structure of the HTS tapes as well as the anomalous skin effect. The results of the numerical investigation performed by the help of the CST PS solver will be presented and discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB267
About •	paper received ※ 18 May 2021 paper accepted ※ 26 July 2021 issue date ※ 12 August 2021
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TUPAB269	Transverse Impedance of Lossy Circular Metal-Dielectric Waveguides	2093
	M. Ivanyan, L.V. Aslyan CANDLE SRI, Yerevan, Armenia K. Flöttmann, F. Lemery DESY, Hamburg, Germany
	The properties of the transverse impedance of a dielectric-loaded metallic circular waveguide are investigated taking into account losses in the outer metallic pipe and in the inner dielectric layer. The dispersion relations, impedances, and wake functions for dipole modes are analyzed and compared for thin and thick dielectric layer cases. The correspondence of the resonant frequencies of the longitudinal monopole and transverse dipole impedances is established.
	Poster TUPAB269 [0.906 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB269
About •	paper received ※ 16 May 2021 paper accepted ※ 28 May 2021 issue date ※ 10 August 2021
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TUPAB270	Thermal Transition Design and Beam Heat-load Estimation for the COLDDIAG Refurbishment	2097
	H.J. Cha, N. Glamann, A.W. Grau, A.-S. Müller, D. Saez de Jauregui KIT, Eggenstein-Leopoldshafen, Germany
	Funding: This work is supported by the BMBF project 05H18VKRB1 HIRING (Federal Ministry of Education and Research). The COLDDIAG (cold vacuum chamber for beam heat load diagnostics) developed at Karlsruhe Institute of Technology has been modified for more studies at cryogenic temperatures different from the previous operations at 4 K in a cold bore and at 50 K in a thermal shield. The key components in this campaign are two thermal transitions connecting both ends of the bore at 50 K with the shield at the same or higher temperature. In this paper, we present design efforts for the compact transitions, allowed heat intakes to the cooling power margin and mechanical robustness in the cryogenic environment. A manufacture scheme for the transition and its peripheral is also given. In addition, the beam heat loads in the refurbished COLDDIAG are estimated in terms of the accelerator beam parameters.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB270
About •	paper received ※ 12 May 2021 paper accepted ※ 02 June 2021 issue date ※ 12 August 2021
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TUPAB272	Observation of Long-Range Wakefield Effects Generated in an Off-Resonance Tesla-Type Cavity	2101
	A.H. Lumpkin, D.R. Edstrom, A. Lunin, P.S. Prieto, J. Ruan, R.M. Thurman-Keup Fermilab, Batavia, Illinois, USA J.A. Diaz Cruz UNM-ECE, Albuquerque, USA J.A. Diaz Cruz, B.T. Jacobson, J.P. Sikora SLAC, Menlo Park, California, USA
	Funding: Work supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics The interest in controlling emittance dilution effects due to off-axis beam transport in accelerator cavities and the resulting dipolar modes is especially important for the facilities with lower emittance beams. The Fermilab Accelerator Science and Technology (FAST) facility has a unique configuration of two single cavities after the photocathode rf gun followed by a cryomodule. The second capture cavity (CC2) was run 15 kHz off resonance and without rf power while a 25-MeV beam was injected into it. The beam centroid effects were tracked by 10 rf button BPMs with bunch-by-bunch position readout capability downstream in a 12-m drift. Possible LRW effects seemed to dominate our previously observed near-resonant HOM effects at mode 14 in this cavity. This mode also shifted in frequency compared to that of the tuned case based on direct measurements. Submacropulse vertical position slewing of 1400 microns at 11 m downstream was observed with a 125 pC/bunch, 50 bunches per macropulse, and 25-MeV beam. The y-position slew amplitudes as a function of z were also measured. Horizontal positions also showed a slew effect. Both are emittance-dilution effects which one wants to mitigate.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB272
About •	paper received ※ 18 May 2021 paper accepted ※ 09 June 2021 issue date ※ 20 August 2021
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TUPAB273	Observations on Submicropulse Electron-Beam Effects From Short-Range Wakefields in Tesla-Type Superconducting Rf Cavities	2105
	A.H. Lumpkin, D.R. Edstrom, P.S. Prieto, J. Ruan, R.M. Thurman-Keup Fermilab, Batavia, Illinois, USA J.A. Diaz Cruz UNM-ECE, Albuquerque, USA J.A. Diaz Cruz, A.L. Edelen, B.T. Jacobson, F. Zhou SLAC, Menlo Park, California, USA
	Funding: Work supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. In previous experiments at the Fermilab Accelerator Science and Technology (FAST) facility, the effects of higher-order modes (HOMs) in TESLA-type cavities on submacropulse centroid motion were elucidated. We now have extended our investigations to short-range wakefields (SRWs) in these cavities. The latter result in submicropulse effects where the transverse wakefields cause head-tail centroid shifts. We used a Hamamatsu C5680 UV-visible synchroscan streak camera to synchronously sum the OTR from each of the 50 micropulses in the macropulse. We generated the y-t effect in the 41-MeV beam by purposely steering the beam off axis in y at the entrance of the first capture cavity. The head-tail transverse kicks within the 11-ps-long micropulses of 500 pC each were observed at the 100-micron level for steering off-axis in one cavity and several 100 microns for two cavities. These SRW results will be compared to simulations from the ASTRA model of a single micropulse in FAST. Since the SRW kicks go inversely with energy, these emittance-dilution effects are particularly relevant to the LCLS-II injector commissioning plans where <1 MeV beam will be injected into a TESLA-type cryomodule. A.H. Lumpkin et al, Phys. Rev. Accel. and Beams 23, 054401 (2020).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB273
About •	paper received ※ 18 May 2021 paper accepted ※ 09 June 2021 issue date ※ 28 August 2021
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TUPAB274	Investigations of Long-Range Wakefield Effects in a TESLA-type Cryomodule at FAST	2109
	A.H. Lumpkin, D.R. Edstrom, P.S. Prieto, J. Ruan, R.M. Thurman-Keup Fermilab, Batavia, Illinois, USA J.A. Diaz Cruz UNM-ECE, Albuquerque, USA J.A. Diaz Cruz, B.T. Jacobson, J.P. Sikora, F. Zhou SLAC, Menlo Park, California, USA
	Funding: Work supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. The preservation of low emittance of electron beams during transport in the accelerating structures of large facilities is an ongoing challenge. In the cases of the TESLA-type superconducting rf cavities currently used in the European X-ray Free-electron Laser (XFEL) and the under-construction Linac Coherent Light Source upgrade (LCLS-II), off-axis beam transport may result in emittance dilution due to transverse long-range wakefields (LRWs) and short-range wakefields (SRW). To investigate such effects, experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility with its unique configuration of two TESLA-type cavities after the photocathode rf gun followed by an 8-cavity cryomodule CM). We generated beam trajectory changes with the H/V125 corrector set located 4 m upstream of the cryomodule. At 125 pC/bunch, 50 bunches, 25-MeV input, and 100-MeV exit energy, we observed for the first time submacropulse position slews of up to 500 microns at locations ~3 m after the CM and a centroid oscillation at a difference frequency of 240 kHz further downstream. Both are emittance-dilution effects which we mitigated with selective upstream beam steering. *W.K.H. Panofsky and M. Bander, Rev. Sci. Instr. 39, 206 (1968).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB274
About •	paper received ※ 18 May 2021 paper accepted ※ 09 June 2021 issue date ※ 31 August 2021
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WEPAB032	Studies of the Short-Range Wakefields for the Electron Storage Ring in the Electron Ion Collider	2675
	G. Wang, M. Blaskiewicz, A. Blednykh, M.P. Sangroula BNL, Upton, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. During the estimates of impedance budget for the Electron Storage Ring (ESR) of Electron-Ion Collider (EIC), various codes, including GdfidL, CST and ECHO3D, have been used to calculate the short-range wake-fields due to the vacuum components. The ECHO 3D code demonstrates more reliable results for the tapered type of structures rather than the GdfidL code, where the stepsize needs to be dramatically decreased to achieve a high-performance calculation. Impedance of the following components are discussed and compared in details: Interaction Region (IR) chamber, bellows, and synchrotron radiation mask (flange absorber).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB032
About •	paper received ※ 19 May 2021 paper accepted ※ 10 June 2021 issue date ※ 24 August 2021
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WEPAB222	Impedance Evaluation of Masks in the HEPS Storage Ring	3145
	N. Wang, S.K. Tian, J.Q. Wang IHEP, Beijing, People’s Republic of China J.Q. Wang University of Chinese Academy of Sciences, Beijing, People’s Republic of China
	Masks are commonly used in photon light sources to protect sensitive elements from synchrotron radiations. In the ultra-low emittance rings, small aperture vacuum chambers are adopted in order to reach the very high gradient in the quadrupoles, while many masks are required due to the high radiation power density. Therefore, the impedance of the masks becomes one of the dominant contributors to the impedance budget. In this paper, the impedance is evaluated among different mask designs. Meanwhile, the impedance cross-talk between adjacent masks is discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB222
About •	paper received ※ 18 May 2021 paper accepted ※ 06 July 2021 issue date ※ 15 August 2021
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WEPAB224	Update of the Transverse Proton Synchrotron Impedance Model	3149
	S. Joly, N. Mounet, B. Salvant CERN, Geneva, Switzerland S. Joly La Sapienza University of Rome, Rome, Italy M. Migliorati INFN-Roma1, Rome, Italy M. Migliorati Sapienza University of Rome, Rome, Italy
	The CERN Proton Synchrotron (PS) was recently upgraded to allow reaching the ambitious performance goal of the High-Luminosity LHC Project. This upgrade is part of the LHC Injectors Upgrade project. The final part of the upgrade was performed during Long Shutdown 2 (LS2) to allow injection at higher energy from the PS Booster and a twofold increase in beam intensity and brightness. These changes must be considered in the PS impedance model. The effect on the impedance of the removal of obsolete injection equipment, changes of several accelerator components and new injection energy will be reviewed, as well as the wall impedance of the elliptic beam pipe, thanks to a newly developed code that allows taking into account both the ellipticity and the non-ultra-relativistic nature of the beam.
	Poster WEPAB224 [0.654 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB224
About •	paper received ※ 17 May 2021 paper accepted ※ 27 July 2021 issue date ※ 17 August 2021
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WEPAB225	Transverse and Longitudinal Single Bunch Instabilities in FCC-ee	3153
	E. Carideo, D. Quartullo, F. Zimmermann CERN, Geneva, Switzerland D. De Arcangelis Sapienza University of Rome, Rome, Italy M. Migliorati, M. Zobov INFN/LNF, Frascati, Italy
	Improving the accuracy of the impedance model of an accelerator is important for keeping beam instabilities and power loss under control. Here, by means of the PyHEAD- TAIL tracking code, we first review the longitudinal mi- crowave instability threshold for FCC-ee by taking into ac- count the longitudinal impedance model evaluated so far. Moreover, we present the results of beam dynamics simula- tions, including both the longitudinal and transverse wake- fields due to the resistive wall, in order to evaluate the influ- ence of the bunch length on the transverse mode coupling instability. The results of the transverse beam dynamics are also compared with the Vlasov solver DELPHI.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB225
About •	paper received ※ 10 May 2021 paper accepted ※ 01 July 2021 issue date ※ 18 August 2021
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THPAB222	Transverse Impedance Coaxial Wire Measurement in an Extended Frequency Range	4227
	E.E. Ergenlik, C. Bruni, D. Le Guidec, P. Lepercq Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France A. Gamelin SOLEIL, Gif-sur-Yvette, France
	The low energy accelerators are tend to have some instabilities especially the beam coupling impedances which comes from the interaction between the beam and accelerator components. As long as the longitudinal impedance are important, transverse impedance determination is crucial for determine the instabilities which will affect the working efficiency of the accelerators. However due to their small amplitudes and measurement setup configuration they are hardly measurable especially in wide frequency ranges. We developed a specific setup for small diameter pieces (28-40mm) for moving and two wire transverse impedance measurements. The dipolar and quadrupolar impedance measurement even with a few Ω level up to 6 GHz for the bellows of ThomX will be presented. Also the comparison with electromagnetic simulations have been performed and can be seen for dipolar impedance measurements.
	Poster THPAB222 [1.578 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB222
About •	paper received ※ 19 May 2021 paper accepted ※ 27 July 2021 issue date ※ 23 August 2021
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THPAB235	Detailed Electromagnetic Characterisation of HL-LHC Low Impedance Collimators	4258
	A. Kurtulus, C. Accentura, N. Biancacci, F. Carra, F. Caspers, N. Chitnis, F. Giordano, R. Illan Fiastre, S. Joly, I. Lamas Garcia, L. Mourier, E. Métral, S. Redaelli, B. Salvant, W. Vollenberg, C. Vollinger, C. Zannini CERN, Geneva, Switzerland
	The High Luminosity Large Hadron Collider (HL-LHC) project will upgrade the LHC machine to allow operation with increased luminosity for the experiments. In order to achieve this goal, different operational parameters of the machine need to be pushed beyond the present design values, including the stored beam energy. One of the main challenges related to the achievement of the upgraded performance is the beam collimation system and its contribution to the overall machine impedance budget. In this perspective, new low impedance collimators have been designed, fabricated, and installed in the LHC. In this study, we will present their detailed electromagnetic (EM) characterization by means of radio frequency (RF) measurements and EM simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB235
About •	paper received ※ 19 May 2021 paper accepted ※ 19 July 2021 issue date ※ 10 August 2021
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THPAB238	An Overview of the Collective Effects and Impedance Calculation for the EIC	4266
	A. Blednykh, D.M. Gassner, B. Podobedov, S. Verdú-Andrés Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA M. Blaskiewicz, C. Hetzel, B. Lepore, V.H. Ranjbar, M.P. Sangroula, P. Thieberger, G. Wang, Q. Wu BNL, Upton, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. A new high-luminosity Electron-Ion Collider (EIC) is being designed at Brookhaven National Laboratory (BNL). Stable operation of the electron beam at an average current of 2.5A within 1100 bunches with a 7mm bunch length is one of the challenging tasks in achieving an electron-proton luminosity of 1033-1034 cm^-2 ses⁻¹ range. Beam induced heating, short-range and long-range wakefield analysis is discussed for some of the vacuum components of the electron storage ring (ESR), the hadron storage ring (HSR), and the rapid cycling synchrotron (RCS) and as well as the impact of the collective effects on the beam stability.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB238
About •	paper received ※ 15 May 2021 paper accepted ※ 24 June 2021 issue date ※ 29 August 2021
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THPAB239	Impedance Optimization of the EIC Interaction Region Vacuum Chamber	4270
	A. Blednykh Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA E.C. Aschenauer, M. Blaskiewicz, C. Hetzel, M.P. Sangroula, G. Wang, H. Witte BNL, Upton, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The interaction region chamber has a complex geometry at the crossing location of electron and proton beam pipes. In the direction of the electron beam, the pipe is designed in a way to avoid joints with cavity characteristics. The horizontal slot on the upstream side and the tapered transition on the downstream side are applied to minimize the IR chamber contribution to the total impedance of the electron ring and to avoid generating Higher Order Modes and heating-related issues. The synchrotron radiation mask is included to protect the IR chamber from synchrotron radiation without significant aperture reduction. In the direction of the proton beam, the main area for optimization is the transition area right after the detector.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB239
About •	paper received ※ 15 May 2021 paper accepted ※ 24 June 2021 issue date ※ 24 August 2021
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THPAB240	Combined Effect of IBS and Impedance on the Longitudinal Beam Dynamics	4274
	A. Blednykh Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA B. Bacha, G. Bassi, T.V. Shaftan, V.V. Smaluk BNL, Upton, New York, USA M. Borland, R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The horizontal/vertical emittances, the bunch length, and the energy spread increase have been studied in the NSLS-II as a function of a single bunch current. The monotonic growth of the horizontal emittance dependence and the energy spread dependence on the single bunch current below the microwave instability threshold can be explained by the Intrabeam Scattering Effect (IBS). The IBS effect results in an increase in the bunch length and the microwave instability thresholds. It was observed experimentally by varying the vertical emittance. To compare with experimental data, particle tracking simulations have been performed with the ELEGANT code including both IBS and the total longitudinal wakefield calculated from the 3D electromagnetic code GdfidL. The same particle tracking simulations have also been applied for the APS-U project, where IBS is predicted to produce only a marginal effect.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB240
About •	paper received ※ 20 May 2021 paper accepted ※ 05 July 2021 issue date ※ 14 August 2021
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Paper

Title

Page

Single Bunch Collective Effects in the EBS Storage Ring

425

L.R. Carver, E. Buratin, N. Carmignani, F. Ewald, L. Hoummi, S.M. Liuzzo, T.P. Perron, B. Roche, S.M. White
ESRF, Grenoble, France

The ESRF storage ring (SR) has been dismantled and replaced by the Extremely Brilliant Source (EBS) which has now been commissioned. Beam based measurements have been performed to characterise the impedance of the new machine and to make a first comparison with predictions. The results from instability threshold scans and tune shift measurements will be presented, as well as bunch length and position variation with current and microwave threshold measurements.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB117

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paper received ※ 11 May 2021 paper accepted ※ 31 May 2021 issue date ※ 25 August 2021

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MOPAB211

Beam Coupling Impedances of Ferrite-Loaded Cavities: Calculations and Measurements

696

S.S. Kurennoy, R.C. McCrady
LANL, Los Alamos, New Mexico, USA

We have developed an efficient method of calculating impedances in cavities with dispersive ferrite dampers. The ferrite dispersive properties in the frequency range of interest are fitted in CST, which allows using both wakefield and lossy eigenmode solvers. A simple test cavity with or without ferrite inserts is explored both numerically and experimentally. The resonance frequencies and beam coupling impedances at cavity resonances are calculated with CST to understand the mode structure. The cavity transverse coupling impedances are also measured on a test stand using a two-wire method. We compare results of impedance calculations and measurements for a few different configurations, with and without ferrites, to ensure a complete understanding of the cavity resonances and their damping with ferrite. These results are important to provide adequate damping of undesired transverse modes in induction-linac cells.

Poster MOPAB211 [1.105 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB211

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paper received ※ 10 May 2021 paper accepted ※ 21 May 2021 issue date ※ 19 August 2021

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TUPAB244

THE WAKEFIELD STUDY OF THE RF-SHIELDED BELLOWS AT THE ILSF STORAGE RING

2015

N. Khosravi, E. Ahmadi, M. Akhyani
ILSF, Tehran, Iran
M. Akhyani
EPFL, Lausanne, Switzerland
A. Khosravi
LAPRI, Tehran, Iran

The corrugated geometry of the bellows made it critical to be shielded with an RF-Shield. Different types of RF shields can be applied to the ILSF vacuum chamber to cover this component’s destructive impedance peaks. Then, the Impedance study and optimization of the RF shields can improve the impedance budget. In this article, two common types of RF shields are simulated in CST software.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB244

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paper received ※ 16 May 2021 paper accepted ※ 02 June 2021 issue date ※ 14 August 2021

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TUPAB245

WAKEFIELD AND HEAT LOAD STUDY OF THE GATE VALVES AT ILSF STORAGE RING

2018

N. Khosravi, E. Ahmadi, M. Akhyani
ILSF, Tehran, Iran
M. Akhyani
EPFL, Lausanne, Switzerland
S. Dastan
IPM, Tehran, Iran
A. Khosravi
LAPRI, Tehran, Iran

As one part of the ILSF storage ring, the rf-shield of the gate valves generates considerable interest in terms of wake impedance and heat-load. Inside the gate valves, there is a vacuity, which causes low frequencies resonances, and it can lead to beam instabilities. Therefore, controlling and eliminating these frequencies will be substantial. A radio frequency rf-shield structure, which conceals this transverse gap of the gate valves, is indispensable for low emittance chambers. This paper analyzes the wake impedance and thermal behavior of a finger-band RF shield in the gate valve.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB245

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paper received ※ 16 May 2021 paper accepted ※ 14 June 2021 issue date ※ 13 August 2021

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TUPAB251

Impedance Studies of a Corrugated Pipe for KARA

2039

S. Maier, M. Brosi, A. Mochihashi, A.-S. Müller, M.J. Nasse, M. Schwarz
KIT, Karlsruhe, Germany

Funding: DFG project 431704792 in the ANR-DFG collaboration project ULTRASYNC and the DFG-funded Doctoral School "Karlsruhe School of Elementary and Astroparticle Physics: Science and Technology".
At the KIT storage ring KARA (KArlsruhe Research Accelerator) it is planned to install an impedance manipulation structure in a versatile chamber to study and eventually control the influence of an additional impedance on the beam dynamics and the emitted coherent synchrotron radiation. For this purpose the impedance of a corrugated pipe is under investigation. In this contribution, we present first results of simulations showing the impact of different structure parameters on its impedance and wake potential.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB251

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paper received ※ 19 May 2021 paper accepted ※ 17 June 2021 issue date ※ 26 August 2021

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TUPAB252

Minimization of NICA Collider Impedance

2043

S.A. Melnikov, I.N. Meshkov
JINR, Dubna, Moscow Region, Russia
K.G. Osipov
JINR/VBLHEP, Dubna, Moscow region, Russia

The paper presents the results of the longitudinal impedance minimization for the beam tube section in the arches of the NICA collider ring, consisting of a pumping pipe, a BPM station, and a bellows assembly, and considers the contribution of the impedance of this section to the ion beam stability in the NICA collider ring. To confirm the efficiency of the optimized design, a BPM prototype was fabricated, and a test bench was built for further laboratory measurements.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB252

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paper received ※ 13 May 2021 paper accepted ※ 14 June 2021 issue date ※ 10 August 2021

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TUPAB255

Longitudinal Beam Dynamics and Coherent Synchrotron Radiation at cSTART

2050

M. Schwarz, E. Bründermann, D. El Khechen, B. Härer, A. Malygin, A.-S. Müller, M.J. Nasse, A.I. Papash, R. Ruprecht, J. Schäfer, M. Schuh, P. Wesolowski
KIT, Karlsruhe, Germany

The compact STorage ring for Accelerator Research and Technology (cSTART) project aims to store electron bunches of LWFA-like beams in a very large momentum acceptance storage ring. The project will be realized at the Karlsruhe Institute of Technology (KIT, Germany). Initially, the Ferninfrarot Linac- Und Test-Experiment (FLUTE), a source of ultra-short bunches, will serve as an injector for cSTART to benchmark and emulate laser-wakefield accelerator-like beams. In a second stage a laser-plasma accelerator will be used as an injector, which is being developed as part of the ATHENA project in collaboration with DESY and Helmholtz Institute Jena (HIJ). With an energy of 50 MeV and damping times of several seconds, the electron beam does not reach equilibrium emittance. Furthermore, the critical frequency of synchrotron radiation is 53 THz and in the same order as the bunch spectrum, which implies that the entire bunch radiates coherently. We perform longitudinal particle tracking simulations to investigate the evolution of the bunch length and spectrum as well as the emitted coherent synchrotron radiation. Finally, different options for the RF system are discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB255

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paper received ※ 17 May 2021 paper accepted ※ 21 June 2021 issue date ※ 29 August 2021

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TUPAB256

Investigation of Damping Effects of the Crab Cavity Noise Induced Emittance Growth

2054

N. Triantafyllou, L.R. Carver, A. Wolski
The University of Liverpool, Liverpool, United Kingdom
F. Antoniou, H. Bartosik, P. Baudrenghien, X. Buffat, R. Calaga, Y. Papaphilippou, N. Triantafyllou
CERN, Meyrin, Switzerland
L.R. Carver
ESRF, Grenoble, France
T. Mastoridis
CalPoly, San Luis Obispo, California, USA

Crab cavities will be installed at the two main interaction points (IP1 and IP5) of the High Luminosity LHC (HL-LHC) in order to minimize the geometric reduction of the luminosity due to the crossing angle. Two prototype crab cavities have been installed into the SPS machine and were tested with a proton beam in 2018, to study the expected emittance growth induced by RF noise. The measured emittance growth was found to be a factor 2-3 lower than predicted from the available analytical and computational models. Damping mechanisms from the transverse impedance, which is not included in the available theories, are studied as a possible explanation for the observed discrepancy.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB256

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paper received ※ 18 May 2021 paper accepted ※ 18 June 2021 issue date ※ 23 August 2021

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TUPAB257

Analysis of Multibunch Spectrum for an Uneven Bunch Distribution in a Storage Ring

2058

R. Li, F. Marhauser
JLab, Newport News, Virginia, USA

Funding: This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.
Modern storage-ring designs often require an uneven bunch distribution pattern. An uneven bunch fill pattern can result in complex structures for the beam current spectra. Particularly at high average beam currents, these complex current spectra need to be taken into account in concern of beam-dynamical effects. In this study, we analyze a beam current spectrum for various filling patterns with bunch trains and gaps. The characteristics of the resulting beam current spectra are illustrated and discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB257

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paper received ※ 21 June 2021 paper accepted ※ 28 June 2021 issue date ※ 12 August 2021

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TUPAB261

The Ferrite Loaded Cavity Impedance Simulation

2070

L. Huang, X. Li, S. Wang, S.Y. Xu
IHEP, Beijing, People’s Republic of China
B. Wu
IHEP CSNS, Guangdong Province, People’s Republic of China

Funding: Work supported by NNSF of China: N0. U1832210
The Rapid Cycling Synchrotron of the China Spallation Neutron Source is a high-intensity proton accelerator, it accumulates the 80 MeV proton beam and accelerates it to 1.6 GeV in 20 ms. The transverse coupling bunch instability is observed in beam commissioning. The source has been investigating from the commissioning. The RF acceleration system consists of eight ferrite-loaded cavities. The impedance is simulated and there is a narrow-band impedance of the ferrite cavity at about 17 MHz

Poster TUPAB261 [1.145 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB261

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paper received ※ 13 May 2021 paper accepted ※ 31 May 2021 issue date ※ 21 August 2021

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TUPAB264

Shielding of CSR Wake in a Drift

2079

G. Stupakov
SLAC, Menlo Park, California, USA

Funding: Work supported by the Department of Energy, contract DE-AC03-76SF00515.
A one-dimensional model of coherent synchrotron radiation (CSR) wakefield developed in Refs. [*,**] is used in computer codes for the simulation of relativistic electron beams. It includes transient effects at the entrance and exit from a bending magnet of finite length. In the ultra-relativistic limit, v=c, the exit CSR wake decays inversely proportional to the distance from the magnet end. To calculate the total energy loss of the beam one needs to integrate this wake to infinity, but the integral diverges. This means that one has to either drop the assumption of the infinite value of the Lorentz factor or take into account the shielding effect of the metal walls in the vacuum chamber. In practice, the latter effect is often dominant. In this work, we derive formulas for the CSR wake in the drift after an exit from the magnet that incorporates the shielding by two parallel metal plates. They allow computing the energy loss of different particles in the beam.
* E. L. Saldin, E. A. Schneidmiller, and M. V. Yurkov. NIMA v. 398, p. 373 (1997).
** G. Stupakov and P. Emma. In: Proceedings of 8th EPAC. Paris, France, 2002, p. 1479.

Poster TUPAB264 [0.661 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB264

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paper received ※ 10 May 2021 paper accepted ※ 25 June 2021 issue date ※ 22 August 2021

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TUPAB265

Bunch Lengthening of the HALF Storage Ring in the Presence of Passive Harmonic Cavities

2082

T.L. He, Z.H. Bai, G.Y. Feng, W. Li, W.W. Li, G. Liu, L. Wang, H. Xu, S.C. Zhang
USTC/NSRL, Hefei, Anhui, People’s Republic of China

A passive 3^rd harmonic RF system, being necessary for the Hefei Advanced Light Facility (HALF) storage ring under design, will be employed to lengthen the bunches for suppressing the intrabeam scattering and improving the beam lifetime. However, the transient beam loading due to the fundamental mode may significantly reduce the bunch lengthening. Since the scale of transient effects is proportional to R/Q, the effects of R/Q on bunch lengthening, in uniform fill pattern with the near-optimum condition fulfilled, are analyzed by multibunches multiparticles tracking simulation. It indicates that the passive superconducting harmonic cavity with a lower R/Q is preferred by HALF.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB265

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paper received ※ 16 May 2021 paper accepted ※ 18 June 2021 issue date ※ 20 August 2021

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TUPAB267

Investigation of Beam Impedance and Heat Load in a High Temperature Superconducting Undulator

2089

D. Astapovych, H. De Gersem, E. Gjonaj
TEMF, TU Darmstadt, Darmstadt, Germany
T.A. Arndt, E. Bründermann, N. Glamann, A.W. Grau, B. Krasch, A.-S. Müller, R. Nast, D. Saez de Jauregui, A. Will
KIT, Eggenstein-Leopoldshafen, Germany

The use of high temperature superconducting (HTS) materials can enhance the performance of superconducting undulators (SCU), which can later be implemented in free electron laser facilities, synchrotron storage rings and light sources. In particular, the short period < 10 mm undulators with narrow magnetic gap < 4 mm are relevant. One of the promising approaches considers a 10 cm meander-structured HTS tapes stacked one above the other. Then, the HTS tape is wound on the SCU. The idea of this jointless undulator has been proposed by, and is being further developed at KIT. Since minimizing the different sources of heat load is a critical issue for all SCUs, a detailed analysis of the impedance and heat load is required to meet the cryogenic system design. The dominant heat source is anticipated to be the resistive surface loss, which is one of the subjects of this study. Considering the complexity of the HTS tape, the impedance model includes the geometrical structure of the HTS tapes as well as the anomalous skin effect. The results of the numerical investigation performed by the help of the CST PS solver will be presented and discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB267

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paper received ※ 18 May 2021 paper accepted ※ 26 July 2021 issue date ※ 12 August 2021

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TUPAB269

Transverse Impedance of Lossy Circular Metal-Dielectric Waveguides

2093

M. Ivanyan, L.V. Aslyan
CANDLE SRI, Yerevan, Armenia
K. Flöttmann, F. Lemery
DESY, Hamburg, Germany

The properties of the transverse impedance of a dielectric-loaded metallic circular waveguide are investigated taking into account losses in the outer metallic pipe and in the inner dielectric layer. The dispersion relations, impedances, and wake functions for dipole modes are analyzed and compared for thin and thick dielectric layer cases. The correspondence of the resonant frequencies of the longitudinal monopole and transverse dipole impedances is established.

Poster TUPAB269 [0.906 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB269

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paper received ※ 16 May 2021 paper accepted ※ 28 May 2021 issue date ※ 10 August 2021

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TUPAB270

Thermal Transition Design and Beam Heat-load Estimation for the COLDDIAG Refurbishment

2097

H.J. Cha, N. Glamann, A.W. Grau, A.-S. Müller, D. Saez de Jauregui
KIT, Eggenstein-Leopoldshafen, Germany

Funding: This work is supported by the BMBF project 05H18VKRB1 HIRING (Federal Ministry of Education and Research).
The COLDDIAG (cold vacuum chamber for beam heat load diagnostics) developed at Karlsruhe Institute of Technology has been modified for more studies at cryogenic temperatures different from the previous operations at 4 K in a cold bore and at 50 K in a thermal shield. The key components in this campaign are two thermal transitions connecting both ends of the bore at 50 K with the shield at the same or higher temperature. In this paper, we present design efforts for the compact transitions, allowed heat intakes to the cooling power margin and mechanical robustness in the cryogenic environment. A manufacture scheme for the transition and its peripheral is also given. In addition, the beam heat loads in the refurbished COLDDIAG are estimated in terms of the accelerator beam parameters.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB270

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paper received ※ 12 May 2021 paper accepted ※ 02 June 2021 issue date ※ 12 August 2021

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TUPAB272

Observation of Long-Range Wakefield Effects Generated in an Off-Resonance Tesla-Type Cavity

2101

A.H. Lumpkin, D.R. Edstrom, A. Lunin, P.S. Prieto, J. Ruan, R.M. Thurman-Keup
Fermilab, Batavia, Illinois, USA
J.A. Diaz Cruz
UNM-ECE, Albuquerque, USA
J.A. Diaz Cruz, B.T. Jacobson, J.P. Sikora
SLAC, Menlo Park, California, USA

Funding: Work supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics
The interest in controlling emittance dilution effects due to off-axis beam transport in accelerator cavities and the resulting dipolar modes is especially important for the facilities with lower emittance beams. The Fermilab Accelerator Science and Technology (FAST) facility has a unique configuration of two single cavities after the photocathode rf gun followed by a cryomodule. The second capture cavity (CC2) was run 15 kHz off resonance and without rf power while a 25-MeV beam was injected into it. The beam centroid effects were tracked by 10 rf button BPMs with bunch-by-bunch position readout capability downstream in a 12-m drift. Possible LRW effects seemed to dominate our previously observed near-resonant HOM effects at mode 14 in this cavity. This mode also shifted in frequency compared to that of the tuned case based on direct measurements. Submacropulse vertical position slewing of 1400 microns at 11 m downstream was observed with a 125 pC/bunch, 50 bunches per macropulse, and 25-MeV beam. The y-position slew amplitudes as a function of z were also measured. Horizontal positions also showed a slew effect. Both are emittance-dilution effects which one wants to mitigate.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB272

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paper received ※ 18 May 2021 paper accepted ※ 09 June 2021 issue date ※ 20 August 2021

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TUPAB273

Observations on Submicropulse Electron-Beam Effects From Short-Range Wakefields in Tesla-Type Superconducting Rf Cavities

2105

A.H. Lumpkin, D.R. Edstrom, P.S. Prieto, J. Ruan, R.M. Thurman-Keup
Fermilab, Batavia, Illinois, USA
J.A. Diaz Cruz
UNM-ECE, Albuquerque, USA
J.A. Diaz Cruz, A.L. Edelen, B.T. Jacobson, F. Zhou
SLAC, Menlo Park, California, USA

Funding: Work supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
In previous experiments at the Fermilab Accelerator Science and Technology (FAST) facility, the effects of higher-order modes (HOMs) in TESLA-type cavities on submacropulse centroid motion were elucidated*. We now have extended our investigations to short-range wakefields (SRWs) in these cavities. The latter result in submicropulse effects where the transverse wakefields cause head-tail centroid shifts. We used a Hamamatsu C5680 UV-visible synchroscan streak camera to synchronously sum the OTR from each of the 50 micropulses in the macropulse. We generated the y-t effect in the 41-MeV beam by purposely steering the beam off axis in y at the entrance of the first capture cavity. The head-tail transverse kicks within the 11-ps-long micropulses of 500 pC each were observed at the 100-micron level for steering off-axis in one cavity and several 100 microns for two cavities. These SRW results will be compared to simulations from the ASTRA model of a single micropulse in FAST. Since the SRW kicks go inversely with energy, these emittance-dilution effects are particularly relevant to the LCLS-II injector commissioning plans where <1 MeV beam will be injected into a TESLA-type cryomodule.
* A.H. Lumpkin et al, Phys. Rev. Accel. and Beams 23, 054401 (2020).

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB273

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paper received ※ 18 May 2021 paper accepted ※ 09 June 2021 issue date ※ 28 August 2021

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TUPAB274

Investigations of Long-Range Wakefield Effects in a TESLA-type Cryomodule at FAST

2109

A.H. Lumpkin, D.R. Edstrom, P.S. Prieto, J. Ruan, R.M. Thurman-Keup
Fermilab, Batavia, Illinois, USA
J.A. Diaz Cruz
UNM-ECE, Albuquerque, USA
J.A. Diaz Cruz, B.T. Jacobson, J.P. Sikora, F. Zhou
SLAC, Menlo Park, California, USA

Funding: *Work supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
The preservation of low emittance of electron beams during transport in the accelerating structures of large facilities is an ongoing challenge. In the cases of the TESLA-type superconducting rf cavities currently used in the European X-ray Free-electron Laser (XFEL) and the under-construction Linac Coherent Light Source upgrade (LCLS-II), off-axis beam transport may result in emittance dilution due to transverse long-range wakefields (LRWs) and short-range wakefields (SRW)***. To investigate such effects, experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility with its unique configuration of two TESLA-type cavities after the photocathode rf gun followed by an 8-cavity cryomodule CM). We generated beam trajectory changes with the H/V125 corrector set located 4 m upstream of the cryomodule. At 125 pC/bunch, 50 bunches, 25-MeV input, and 100-MeV exit energy, we observed for the first time submacropulse position slews of up to 500 microns at locations ~3 m after the CM and a centroid oscillation at a difference frequency of 240 kHz further downstream. Both are emittance-dilution effects which we mitigated with selective upstream beam steering.
***W.K.H. Panofsky and M. Bander, Rev. Sci. Instr. 39, 206 (1968).

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB274

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paper received ※ 18 May 2021 paper accepted ※ 09 June 2021 issue date ※ 31 August 2021

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WEPAB032

Studies of the Short-Range Wakefields for the Electron Storage Ring in the Electron Ion Collider

2675

G. Wang, M. Blaskiewicz, A. Blednykh, M.P. Sangroula
BNL, Upton, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
During the estimates of impedance budget for the Electron Storage Ring (ESR) of Electron-Ion Collider (EIC), various codes, including GdfidL, CST and ECHO3D, have been used to calculate the short-range wake-fields due to the vacuum components. The ECHO 3D code demonstrates more reliable results for the tapered type of structures rather than the GdfidL code, where the stepsize needs to be dramatically decreased to achieve a high-performance calculation. Impedance of the following components are discussed and compared in details: Interaction Region (IR) chamber, bellows, and synchrotron radiation mask (flange absorber).

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB032

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paper received ※ 19 May 2021 paper accepted ※ 10 June 2021 issue date ※ 24 August 2021

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WEPAB222

Impedance Evaluation of Masks in the HEPS Storage Ring

3145

N. Wang, S.K. Tian, J.Q. Wang
IHEP, Beijing, People’s Republic of China
J.Q. Wang
University of Chinese Academy of Sciences, Beijing, People’s Republic of China

Masks are commonly used in photon light sources to protect sensitive elements from synchrotron radiations. In the ultra-low emittance rings, small aperture vacuum chambers are adopted in order to reach the very high gradient in the quadrupoles, while many masks are required due to the high radiation power density. Therefore, the impedance of the masks becomes one of the dominant contributors to the impedance budget. In this paper, the impedance is evaluated among different mask designs. Meanwhile, the impedance cross-talk between adjacent masks is discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB222

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paper received ※ 18 May 2021 paper accepted ※ 06 July 2021 issue date ※ 15 August 2021

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WEPAB224

Update of the Transverse Proton Synchrotron Impedance Model

3149

S. Joly, N. Mounet, B. Salvant
CERN, Geneva, Switzerland
S. Joly
La Sapienza University of Rome, Rome, Italy
M. Migliorati
INFN-Roma1, Rome, Italy
M. Migliorati
Sapienza University of Rome, Rome, Italy

The CERN Proton Synchrotron (PS) was recently upgraded to allow reaching the ambitious performance goal of the High-Luminosity LHC Project. This upgrade is part of the LHC Injectors Upgrade project. The final part of the upgrade was performed during Long Shutdown 2 (LS2) to allow injection at higher energy from the PS Booster and a twofold increase in beam intensity and brightness. These changes must be considered in the PS impedance model. The effect on the impedance of the removal of obsolete injection equipment, changes of several accelerator components and new injection energy will be reviewed, as well as the wall impedance of the elliptic beam pipe, thanks to a newly developed code that allows taking into account both the ellipticity and the non-ultra-relativistic nature of the beam.

Poster WEPAB224 [0.654 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB224

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paper received ※ 17 May 2021 paper accepted ※ 27 July 2021 issue date ※ 17 August 2021

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WEPAB225

Transverse and Longitudinal Single Bunch Instabilities in FCC-ee

3153

E. Carideo, D. Quartullo, F. Zimmermann
CERN, Geneva, Switzerland
D. De Arcangelis
Sapienza University of Rome, Rome, Italy
M. Migliorati, M. Zobov
INFN/LNF, Frascati, Italy

Improving the accuracy of the impedance model of an accelerator is important for keeping beam instabilities and power loss under control. Here, by means of the PyHEAD- TAIL tracking code, we first review the longitudinal mi- crowave instability threshold for FCC-ee by taking into ac- count the longitudinal impedance model evaluated so far. Moreover, we present the results of beam dynamics simula- tions, including both the longitudinal and transverse wake- fields due to the resistive wall, in order to evaluate the influ- ence of the bunch length on the transverse mode coupling instability. The results of the transverse beam dynamics are also compared with the Vlasov solver DELPHI.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB225

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paper received ※ 10 May 2021 paper accepted ※ 01 July 2021 issue date ※ 18 August 2021

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THPAB222

Transverse Impedance Coaxial Wire Measurement in an Extended Frequency Range

4227

E.E. Ergenlik, C. Bruni, D. Le Guidec, P. Lepercq
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
A. Gamelin
SOLEIL, Gif-sur-Yvette, France

The low energy accelerators are tend to have some instabilities especially the beam coupling impedances which comes from the interaction between the beam and accelerator components. As long as the longitudinal impedance are important, transverse impedance determination is crucial for determine the instabilities which will affect the working efficiency of the accelerators. However due to their small amplitudes and measurement setup configuration they are hardly measurable especially in wide frequency ranges. We developed a specific setup for small diameter pieces (28-40mm) for moving and two wire transverse impedance measurements. The dipolar and quadrupolar impedance measurement even with a few Ω level up to 6 GHz for the bellows of ThomX will be presented. Also the comparison with electromagnetic simulations have been performed and can be seen for dipolar impedance measurements.

Poster THPAB222 [1.578 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB222

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paper received ※ 19 May 2021 paper accepted ※ 27 July 2021 issue date ※ 23 August 2021

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THPAB235

Detailed Electromagnetic Characterisation of HL-LHC Low Impedance Collimators

4258

A. Kurtulus, C. Accentura, N. Biancacci, F. Carra, F. Caspers, N. Chitnis, F. Giordano, R. Illan Fiastre, S. Joly, I. Lamas Garcia, L. Mourier, E. Métral, S. Redaelli, B. Salvant, W. Vollenberg, C. Vollinger, C. Zannini
CERN, Geneva, Switzerland

The High Luminosity Large Hadron Collider (HL-LHC) project will upgrade the LHC machine to allow operation with increased luminosity for the experiments. In order to achieve this goal, different operational parameters of the machine need to be pushed beyond the present design values, including the stored beam energy. One of the main challenges related to the achievement of the upgraded performance is the beam collimation system and its contribution to the overall machine impedance budget. In this perspective, new low impedance collimators have been designed, fabricated, and installed in the LHC. In this study, we will present their detailed electromagnetic (EM) characterization by means of radio frequency (RF) measurements and EM simulations.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB235

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paper received ※ 19 May 2021 paper accepted ※ 19 July 2021 issue date ※ 10 August 2021

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THPAB238

An Overview of the Collective Effects and Impedance Calculation for the EIC

4266

A. Blednykh, D.M. Gassner, B. Podobedov, S. Verdú-Andrés
Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA
M. Blaskiewicz, C. Hetzel, B. Lepore, V.H. Ranjbar, M.P. Sangroula, P. Thieberger, G. Wang, Q. Wu
BNL, Upton, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
A new high-luminosity Electron-Ion Collider (EIC) is being designed at Brookhaven National Laboratory (BNL). Stable operation of the electron beam at an average current of 2.5A within 1100 bunches with a 7mm bunch length is one of the challenging tasks in achieving an electron-proton luminosity of 1033-1034 cm^-2 ses⁻¹ range. Beam induced heating, short-range and long-range wakefield analysis is discussed for some of the vacuum components of the electron storage ring (ESR), the hadron storage ring (HSR), and the rapid cycling synchrotron (RCS) and as well as the impact of the collective effects on the beam stability.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB238

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paper received ※ 15 May 2021 paper accepted ※ 24 June 2021 issue date ※ 29 August 2021

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THPAB239

Impedance Optimization of the EIC Interaction Region Vacuum Chamber

4270

A. Blednykh
Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA
E.C. Aschenauer, M. Blaskiewicz, C. Hetzel, M.P. Sangroula, G. Wang, H. Witte
BNL, Upton, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
The interaction region chamber has a complex geometry at the crossing location of electron and proton beam pipes. In the direction of the electron beam, the pipe is designed in a way to avoid joints with cavity characteristics. The horizontal slot on the upstream side and the tapered transition on the downstream side are applied to minimize the IR chamber contribution to the total impedance of the electron ring and to avoid generating Higher Order Modes and heating-related issues. The synchrotron radiation mask is included to protect the IR chamber from synchrotron radiation without significant aperture reduction. In the direction of the proton beam, the main area for optimization is the transition area right after the detector.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB239

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paper received ※ 15 May 2021 paper accepted ※ 24 June 2021 issue date ※ 24 August 2021

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THPAB240

Combined Effect of IBS and Impedance on the Longitudinal Beam Dynamics

4274

A. Blednykh
Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA
B. Bacha, G. Bassi, T.V. Shaftan, V.V. Smaluk
BNL, Upton, New York, USA
M. Borland, R.R. Lindberg
ANL, Lemont, Illinois, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy.
The horizontal/vertical emittances, the bunch length, and the energy spread increase have been studied in the NSLS-II as a function of a single bunch current. The monotonic growth of the horizontal emittance dependence and the energy spread dependence on the single bunch current below the microwave instability threshold can be explained by the Intrabeam Scattering Effect (IBS). The IBS effect results in an increase in the bunch length and the microwave instability thresholds. It was observed experimentally by varying the vertical emittance. To compare with experimental data, particle tracking simulations have been performed with the ELEGANT code including both IBS and the total longitudinal wakefield calculated from the 3D electromagnetic code GdfidL. The same particle tracking simulations have also been applied for the APS-U project, where IBS is predicted to produce only a marginal effect.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB240

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paper received ※ 20 May 2021 paper accepted ※ 05 July 2021 issue date ※ 14 August 2021

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