IPAC2017 - Classification: 05 Beam Dynamics and Electromagnetic Fields / D05 Coherent and Incoherent Instabilities

Paper	Title	Page
MOZA1	Electron Cloud Effects at the LHC and LHC Injectors	30
	G. Rumolo, H. Bartosik, E. Belli, P. Dijkstal, G. Iadarola, K.S.B. Li, L. Mether, A. Romano, M. Schenk, F. Zimmermann CERN, Geneva, Switzerland E. Belli University of Rome La Sapienza, Rome, Italy P. Dijkstal TU Darmstadt, Darmstadt, Germany M. Schenk EPFL, Lausanne, Switzerland
	Electron cloud effects are one of the main limitations of the performance of the LHC and its injectors. Enormous progress has been done in the simulation of the electron cloud build-up and of the effects on beam stability while mitigation measures have been identified and implemented (scrubbing, low secondary electron yield coatings, etc.). The above has allowed reaching nominal beam parameters in the LHC during Run 2. A review of the studies and results obtained and the strategy and expected performance for the High Luminosity operation of the LHC will be presented.
	Slides MOZA1 [12.855 MB]
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WEOAB3	RF Quadrupole Structures for Transverse Landau Damping in Circular Accelerators	2516
	M. Schenk, X. Buffat, L.R. Carver, A. Grudiev, K.S.B. Li, E. Métral, K. Papke CERN, Geneva, Switzerland A. Maillard ENS, Paris, France
	The beams required for the high luminosity upgrade of the Large Hadron Collider (HL-LHC) and other potential future circular colliders (FCC) call for efficient mechanisms to suppress transverse collective instabilities. In addition to octupole magnets installed for the purpose of Landau damping in the transverse planes, we propose to use radio frequency (rf) quadrupole structures to considerably enhance the aforementioned stabilising effect. By means of the PyHEADTAIL macroparticle tracking code as well as analytical studies, the stabilising mechanism introduced by an rf quadrupole is studied and explained. It is, furthermore, compared to the influence of the second order chromaticity on transverse beam stability.
	Slides WEOAB3 [2.537 MB]
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THPAB001	Microbunching Instability as a Caustic Phenomenon	3676
SUSPSIK053	use link to see paper's listing under its alternate paper code
	T.K. Charles, D.M. Paganin Monash University, Faculty of Science, Clayton, Victoria, Australia M.J. Boland The University of Melbourne, Melbourne, Victoria, Australia M.J. Boland, R.T. Dowd SLSA, Clayton, Australia
	Microbunching instability if left alone, threatens to degrade the beam quality of high brightness electron beams in Free Electron Lasers. Recently, caustic formation in electron trajectories was identified as a mechanism describing current modulations in accelerated particle beams. Here we consider CSR-induced microbunching as a caustic phenomenon. This analysis reports on the influence of longitudinal dispersion, R56, on the microbunching process, as well as elucidating the influence of the second and third order longitudinal dispersion values, T566 and U5666.
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THPAB002	Update of the Collective Effects Studies for Sirius	3680
	F.H. de Sá, H.O.C. Duarte, L. Liu LNLS, Campinas, Brazil
	An updated impedance budget for Sirius, with contributions from 3D electromagnetic simulations and analytic calculations, is presented and the estimates for single and multi-bunch instability thresholds for the first operation phase are re-evaluated.
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THPAB003	Harmonic RF System for the ESRF EBS	3684
	N. Carmignani, J. Jacob, B. Nash, S.M. White ESRF, Grenoble, France
	A harmonic RF system for bunch lengthening to increase the Touschek lifetime of the ESRF Extemely Brilliant Source (EBS) is under study. Multiparticle simulations have been performed to study the bunch lengthening and the bunch shape with impedance effect and with third or fourth harmonic cavities. The effect of a harmonic RF system on the microwave instability is studied, finding an increase in the threshold. The AC Robinson instability threshold with a superconducting harmonic cavity has been studied with multiparticle simulations.
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THPAB005	Improvement of the Analytic Vlasov Solver DELPHI	3688
	D. Amorim Université Grenoble Alpes, Grenoble, France N. Biancacci, K.S.B. Li, E. Métral CERN, Geneva, Switzerland
	The simulation code DELPHI is an analytic Vlasov solver which allows to evaluate the beam transverse stability with respect to impedance effects. It allows to perform fast scans over parameters such as chromaticity, damper gain or beam intensity for a given impedance model and particle distribution. In order to improve the simulation code, new longitudinal particle distributions have been implemented. The simulations results obtained with these distributions are compared to theoretical predictions. An additional post-processing of DELPHI's output has also been implemented, allowing to reconstruct the signal seen by head-tail stripline monitors, in particular in presence of bunch-by-bunch damper. The results are compared to theoretical models, to pyHEADTAIL simulations and to measurements performed in the LHC.
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THPAB006	Nuage, Ion Cloud Tracker	3692
SUSPSIK054	use link to see paper's listing under its alternate paper code
	A. Gamelin, C. Bruni, D. Radevych LAL, Orsay, France
	Funding: Work is supported by ANR-10-EQPX-51, by grants from Région Ile-de- France, IN2P3 and Pheniics Doctoral School. NUAGE is a data parallel Matlab code which simulates the ion cloud effect in electron storage rings. The ion cloud is tracked in the ring taking into account the transverse and longitudinal effect of the beam-ion interaction, tracking in magnetic elements, usage of electrodes and gaps as clearing means. This program has been used to compute ionised ion equilibrium state and its neutralisation factor. In this article the NUAGE code is presented. The model, analysis method and performances are discussed.
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THPAB007	Short Bunches at the Transition From Strong to Weak Longitudinal Instability	3696
	P. Kuske HZB, Berlin, Germany
	The interaction of particles with their vacuum sur-roundings can lead to longitudinal instabilities of the whole bunch of particles. Most of these instabilities are strong and the growth rates are large compared to the damping rate. For a weak instability the opposite is true and with just a resistive impedance the instability would always be weak and independent of the bunch length. The interaction of a bunch with its own radiation emitted midway between parallel plates leads to a strong instabil-ity for long bunches and a transition to weak instability if the bunch length becomes shorter. This regime is ana-lysed numerically with a Vlasov-Fokker-Planck solver. The results are compared to recent observations at ANKA. An attempt is made to explain the remaining discrepan-cies by including higher order terms of the momentum compaction factor into these calculations. There are indi-cations that the simple model needs refinements in order to take radiation from upstream dipoles into account.
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THPAB014	An Adaptive Mesh-Based Method for the Efficient Simulation of LSC-Driven Microbunching Gain in FEL Applications	3720
	Ph. Amstutz University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany M. Vogt DESY, Hamburg, Germany
	Electron beams with high peak current as they are required for the operation of free-electron lasers (FELs) are often generated by means of a series of magnetic bunch compressors. In conjunction with a collective coherent force, e.g. longitudinal space-charge (LSC), bunch compressors can possibly cause a wavelength dependent amplification of initial density inhomogeneities, potentially to an extent detrimental to the operation of the FEL. A common model, consisting of LSC, acceleration (kicks), and magnetic chicanes (drift-type maps), is governed by a time-discrete Vlasov-Poisson system. Such systems have been successfully simulated using mesh based representations of the phase space density (PSD) and the method of characteristics for the update step. However, for the irregular and exotic PSDs, prevalent in FEL applications, a homogeneous high resolution discretization on a naive rectangular mesh can be prohibitively wasteful. Here we present an approach based on adaptive tree refinement that addresses the complexity of the PSDs and allows for the efficient simulation of LSC-driven micro-bunching in FELs.
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THPAB020	Coupling Impedances and Collective Effects for FCC-ee	3734
	E. Belli, M. Migliorati University of Rome La Sapienza, Rome, Italy G. Castorina, B. Spataro, M. Zobov INFN/LNF, Frascati (Roma), Italy A. Novokhatski SLAC, Menlo Park, California, USA S. Persichelli LBNL, Berkeley, California, USA
	A very important issue for the Future Circular Collider (FCC) is represented by collective effects due to the self-induced electromagnetic fields, which, acting back on the beam, could produce dangerous instabilities. In this paper we will focus our work on the FCC electron-positron machine: in particular we will study some important sources of wake fields, their coupling impedances and the impact on the beam dynamics. We will also discuss longitudinal and transverse instability thresholds, both for single bunch and multibunch, and indicate some ways to mitigate such instabilities.
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THPAB025	Simulation Studies of Transverse Beam Instabilities and Measures Beyond 1 MW Beam Power in the 3-GeV RCS of J-PARC	3750
	P.K. Saha, H. Hotchi, Y. Shobuda JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
	The transverse impedance of the extraction kicker magnets is a significant beam instability source in the 3-GeV RCS (Rapid Cycling Synchrotron) of J-PARC (Japan Proton Accelerator Research Complex). The systematic simulation studies for beam instability by including the space charge effect has been done by using the ORBIT code. The simulation results are well reproduced in the corresponding measurements. The designed 1 MW beam power has recently been accomplished by keeping sextuple magnets off in order to stabilize the beam by utilizing the large lattice chromaticity throughout the entire acceleration period. The RCS simultaneously delivers extracted beam to the MLF (Material and Life Science Experimental Facility) and the MR (Main Ring). In order to ensure 1 MW beam power at the MLF even when RCS beam sharing to the MR is twice increased as well as when a second target station is constructed at the MLF, a beam power of 1.5 MW has to be realized in the RCS. However, the simulation shows that beyond 1 MW the beam is unstable even if no chromaticity is corrected. A reduction of the kicker impedance by at least a half is required in order to achieve 1.5 MW beam power in the RCS.
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THPAB026	Feasibility Analysis of Emittance Preservation During Bunch Compression in the Presence of Coherent Synchrotron Radiation in an Arc	3753
SUSPSIK055	use link to see paper's listing under its alternate paper code
	X.Y. Huang, X. Cui, S. Gu, Y. Jiao, G. Xu IHEP, Beijing, People's Republic of China
	Electron beam with low transverse emittance, short bunch length and high peak current is the basic requirement in modern high-brightness light sources. However, coherent synchrotron radiation (CSR) will dilute the transverse emittance when the electron beams pass through a magnetic bunch compressor and degrade the performance of the machine. In this paper, based on our CSR point-kick analysis, arc compressors with high compression factor in the presence of CSR effect are studied, both periodic and aperiodic arcs are included. Through analytical and numerical research, an easy optics design technique is introduced to minimize the emittance dilution within these compressors. Taking practical considerations into account, the results of periodic and aperiodic arcs are compared.
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THPAB029	Simulation of the Single Bunch Instabilities for the High Energy Photon Source	3760
	Z. Duan, N. Wang, H.S. Xu IHEP, Beijing, People's Republic of China
	Funding: Work supported by Natural Science Foundation of China (No.11605212). Timing modes pursing a large single bunch charge will be important operation modes for the green-field High Energy Photon Source (HEPS). The single bunch instabilities are simulated with the elegant tracking code, based on the current impedance budget. In particular, a novel on-axis accumulation scheme* based on the RF gymnastics of an active double-RF system was proposed as a candidate injection scheme for HEPS, while the zero-current rms bunch length dramatically decreases during the injection, from 32 mm to 3 mm, over a time duration of about 200 ms. The single bunch instabilities are evaluated for both the operation mode with optimal bunch lengthening as well as the injection mode with the very short bunch length, as a first step in understanding the possible beam instability for this injection scheme. * G. Xu, et al., in Proc. IPAC'16, pp. 2886-2888. Z. Duan, et al., in Proc. eeFACT 2016.
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THPAB030	Studies on Collective Instabilities in HEPS	3763
	N. Wang, Z. Duan, C. Li, S.K. Tian, H.S. Xu IHEP, Beijing, People's Republic of China
	The High Energy Photon Source (HEPS) is a new designed photon source at beam energy of 6 GeV. Due to the small beam size and increased coupling impedance with the restricted beam pipe aperture, the collective effects may bring new challenges to the physical design of the machine. The collective instabilities are estimated for different operation mode. The critical instability issues are also identified for each mode.
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THPAB031	Study of Beam Break Up in Irradiation Linacs	3767
SUSPSIK056	use link to see paper's listing under its alternate paper code
	X.C. Meng, H.B. Chen, W. Gai, J. Shi, S.X. Zheng TUB, Beijing, People's Republic of China G.H. Li, J.S. Liu, Y.H. Liu NUCTECH, Beijing, People's Republic of China F.H. de Sá LNLS, Campinas, Brazil
	Many recent experiments of the irradiation linacs produced at Tsinghua University indicate that beam power is limited by beam break up (BBU). Limits exist while the beam current or the pulse width is increased. In this paper, we illustrate the bream break up (BBU) phenomenon in the cases of both the 10MeV travelling-wave linac and 10MeV backward travelling-wave linac. The higher order modes in the linacs are analysed and the wake fields are calculated both with theoretical analysis and numerical simulation. Also, the beam dynamics is studied on the basis of the wakefield results to find a BBU threshold in these structures.
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THPAB032	Estimates of Collective Effects in the HALS Storage Ring Having the First Version Lattice	3770
SUSPSIK057	use link to see paper's listing under its alternate paper code
	N. Hu, Z.H. Bai, W. Li, Q. Luo, L. Wang USTC/NSRL, Hefei, Anhui, People's Republic of China
	The Hefei Advanced Light Source (HALS) is a diffraction-limited storage ring with a beam energy of 2.0 GeV. Recently the first version lattice has been designed for the HALS storage ring, and the natural emittance is about 18 pm·rad. In this paper, we study the collective effects in this storage ring, including calculations of intra-beam scattering effect and Touschek lifetime, and estimates of the thresholds of some single-bunch and multi-bunch instabilities.
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THPAB040	Destabilising Effect of Linear Coupling in the LHC	3791
	L.R. Carver, D. Amorim, N. Biancacci, X. Buffat, K.S.B. Li, E. Métral, B. Salvant, M. Schenk CERN, Geneva, Switzerland
	During operation in 2015 and 2016, some transverse instabilities were observed when either the coupling (or closest tune approach) C- was large, or when the tunes were moved closer together. This motivated a campaign of simulations on the effect of linear coupling on the transverse stability. Measurements made during operation and with dedicated beam time have been found to confirm the predictions. This paper will detail the results of the linear coupling studies and relate them to operation of the LHC in the future.
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THPAB053	Laser Heater Deisgn for the CLARA FEL Test Facility	3833
	A.D. Brynes, S.P. Jamison, B.D. Muratori, N. Thompson, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S.P. Jamison, B.D. Muratori, N. Thompson, P.H. Williams Cockcroft Institute, Warrington, Cheshire, United Kingdom
	We present considerations of microbunching studies in the CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility under construction at Daresbury Laboratory. CLARA, a high-brightness electron linac, presents an opportunity to study the microbunching instability. A number of theoretical models have been proposed concerning the causes of this instability, and it has also been observed at various FEL facilities. We have applied these models to the CLARA FEL, and propose a suitable laser heater design which will provide flexibility in terms of the range of modes of operation for CLARA. We also propose a method for inducing and controlling the microbunching instability via pulse stacking of the photoinjector laser.
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THPAB059	CSR and Space Charge Studies for the CLARA Phase 1 Beamline	3851
	B.S. Kyle, R.B. Appleby UMAN, Manchester, United Kingdom J.K. Jones, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom M.J. de Loos, S.B. van der Geer Pulsar Physics, Eindhoven, The Netherlands
	The installation of Phase 1 of CLARA, the UK's new FEL test facility, is currently underway at Daresbury Laboratory. When completed, it will be able to deliver 45 MeV electron beams to the pre-existing VELA beamline, which runs parallel. Phase 1 consists of a 10 Hz photocathode gun, a 2 m long S-band travelling wave linac, a spectrometer line, and associated optics and diagnostics. A detailed study into the beam dynamics of the lattice is presented, with a focus towards the effects of space charge and coherent synchrotron radiation on the electron bunch. Simulations disagreed with predictions from a one-dimensional model of coherent radiation, and this disagreement is believed to be due to a violation of the Derbenev criterion.
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THPAB076	Coherent Synchrotron Radiation Simulations for Off-Axis Beams Using the Bmad Toolkit	3887
	D. Sagan, C.E. Mayes Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Coherent synchrotron radiation (CSR) potentially limits operation accelerators with high bunch charges and/or short bunch lengths by increasing energy spread, and by Except at the lowest beam energies, the one dimensional treatment of coherent synchrotron radiation (CSR) originally developed by Saldin is an efficient and reasonably accurate way to simulate the effects of CSR on a particle beam. A possible problem with standard implementations of the 1D CSR formalism is that these implementations assume that the beam centroid is close to the reference trajectory that defines the lattice. In this paper, the one dimensional treatment is extended to take into account beams whose centroid is far from the reference trajectory and an example using the Cornell-BNL Fixed Field Alternating Gradient (FFAG) accelerator CBETA is given.
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THPAB078	Beam Dynamics Studies of the Transverse Gradient Undulator and Its Application to Suppression of Microbunching Instability	3895
	T. Liu, Y. Ding, Z. Huang, W. Qin SLAC, Menlo Park, California, USA T. Liu University of Chinese Academy of Sciences, Beijing, People's Republic of China T. Liu, D. Wang SINAP, Shanghai, People's Republic of China
	A transverse gradient undulator (TGU) which was initially proposed for high gain free electron lasers (FELs) driven by electron beams with relatively large energy spread, can be extended to the application of beam dynamics, such as phase-merging enhanced harmonic generation FEL and suppression of microbunching instability. In this contribution we present beam dynamics studies of the TGU, analyze the resulting focusing and dispersion, and discuss the effects of an additional corrector on the TGU. As an application to beam dynamics, we show a feasible transport system based on the TGU as a reversible electron beam heater to suppress the microbunching instability of the electron beam.
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THPAB080	Estimations of Coherent Instabilities for JLEIC	3903
	R. Li JLab, Newport News, Virginia, USA
	Funding: Work supported by the Department of Energy, Laboratory Directed Research and Development Funding, under Contract No. DE-AC05-06OR23177 JLEIC is the medium energy electron-ion collider currently under active design at Jefferson Lab. The design goals of JLEIC are both high luminosity (1033-1034 cm^-2ses⁻¹) and high polarization (>70%) for the electron and light ion beams, for a wide range of electron and ion beam energies and for a wide spectrum of ion species. The unprecedented luminosity goal for this electron-ion collider sets strong requirements for the understanding and management of potential collective effects in JLEIC. In this paper, we present preliminary estimations of single and coupled bunch coherent instabilities for the electron and proton beams at collision energies for the JLEIC design. Further improvement of the estimations and mitigation methods are discussed. MEIC design summary, http://arxiv.org/ftp/arxiv/papers/1504/1504.07961.pdf, (2015).
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THPVA010	Electron Cloud Simulations for the Main Ring of J-PARC	4436
	B. Yee-Rendón, R. Muto, K. Ohmi, K. Satou, M. Tomizawa, T. Toyama KEK, Ibaraki, Japan
	The simulation of beam instabilities is a helpful tool to evaluate potential threats against the machine protection of the high intensity beams. At Main Ring (MR) of J-PARC, signals related to the electron cloud have been observed during the slow beam extraction mode. Hence, several studies were conducted to investigate the mechanism that produces it, the results confirmed a strong dependence on the beam intensity and the bunch structure in the formation of the electron cloud, however, the precise explanation of its trigger conditions remains incomplete. To shed light on the problem, electron cloud simulations were done using an updated version of the computational model developed from previous works at KEK. The code employed the signals of the measurements to reproduce the events seen during the surveys.
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THPVA084	Evaluation of Collective Effects in Iranian Light Source Facility (ILSF) Storage Ring	4650
	E. Ahmadi, S. Ahmadiannamin, J. Rahighi ILSF, Tehran, Iran S.M. Jazayeri IUST, Narmac, Tehran, Iran
	In this paper, we present the calculations of various collective effects in the storage ring of ILSF, a synchrotron light source under design in Iran. The ILSF storage ring is based on 5-BA lattice structure and emittance of 270 pm-rad which is optimized to provide high brightness and flux photons for the users. Because of design features, small radius vacuum pipe and small momentum compaction factor of lattice, it is expected that instabilities emerging from collective effects will affect significantly the beam quality and make it is challenging to reach maximum designed beam current. We will address the results of beam quality degradation and threshold calculations for different singlebunch and multibunch instabilities.
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THPVA143	Beam-Breakup Studies for the 4-Pass Cornell-Brookhaven Energy Recovery LINAC Test Accelerator	4801
	W. Lou, J.A. Crittenden, G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cornell University and Brookhaven National Laboratory are currently designing the Cornell-BNL ERL Test Accelerator (CBETA). To be built at Cornell's Wilson Lab, CBETA utilizes the existing ERL injector and main linac cryomodule (MLC). As the electron bunches pass through the MLC cavities, higher order modes (HOMs) are excited. The recirculating bunches interact with the HOMs, which can give rise to beam-breakup instability (BBU). Here we present simulation results on how BBU limits the maximum achievable current, and potential ways to improve the threshold current.
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Paper

Title

Page

Electron Cloud Effects at the LHC and LHC Injectors

30

G. Rumolo, H. Bartosik, E. Belli, P. Dijkstal, G. Iadarola, K.S.B. Li, L. Mether, A. Romano, M. Schenk, F. Zimmermann
CERN, Geneva, Switzerland
E. Belli
University of Rome La Sapienza, Rome, Italy
P. Dijkstal
TU Darmstadt, Darmstadt, Germany
M. Schenk
EPFL, Lausanne, Switzerland

Electron cloud effects are one of the main limitations of the performance of the LHC and its injectors. Enormous progress has been done in the simulation of the electron cloud build-up and of the effects on beam stability while mitigation measures have been identified and implemented (scrubbing, low secondary electron yield coatings, etc.). The above has allowed reaching nominal beam parameters in the LHC during Run 2. A review of the studies and results obtained and the strategy and expected performance for the High Luminosity operation of the LHC will be presented.

Slides MOZA1 [12.855 MB]

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WEOAB3

RF Quadrupole Structures for Transverse Landau Damping in Circular Accelerators

2516

M. Schenk, X. Buffat, L.R. Carver, A. Grudiev, K.S.B. Li, E. Métral, K. Papke
CERN, Geneva, Switzerland
A. Maillard
ENS, Paris, France

The beams required for the high luminosity upgrade of the Large Hadron Collider (HL-LHC) and other potential future circular colliders (FCC) call for efficient mechanisms to suppress transverse collective instabilities. In addition to octupole magnets installed for the purpose of Landau damping in the transverse planes, we propose to use radio frequency (rf) quadrupole structures to considerably enhance the aforementioned stabilising effect. By means of the PyHEADTAIL macroparticle tracking code as well as analytical studies, the stabilising mechanism introduced by an rf quadrupole is studied and explained. It is, furthermore, compared to the influence of the second order chromaticity on transverse beam stability.

Slides WEOAB3 [2.537 MB]

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THPAB001

Microbunching Instability as a Caustic Phenomenon

3676

SUSPSIK053

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T.K. Charles, D.M. Paganin
Monash University, Faculty of Science, Clayton, Victoria, Australia
M.J. Boland
The University of Melbourne, Melbourne, Victoria, Australia
M.J. Boland, R.T. Dowd
SLSA, Clayton, Australia

Microbunching instability if left alone, threatens to degrade the beam quality of high brightness electron beams in Free Electron Lasers. Recently, caustic formation in electron trajectories was identified as a mechanism describing current modulations in accelerated particle beams. Here we consider CSR-induced microbunching as a caustic phenomenon. This analysis reports on the influence of longitudinal dispersion, R56, on the microbunching process, as well as elucidating the influence of the second and third order longitudinal dispersion values, T566 and U5666.

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THPAB002

Update of the Collective Effects Studies for Sirius

3680

F.H. de Sá, H.O.C. Duarte, L. Liu
LNLS, Campinas, Brazil

An updated impedance budget for Sirius, with contributions from 3D electromagnetic simulations and analytic calculations, is presented and the estimates for single and multi-bunch instability thresholds for the first operation phase are re-evaluated.

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THPAB003

Harmonic RF System for the ESRF EBS

3684

N. Carmignani, J. Jacob, B. Nash, S.M. White
ESRF, Grenoble, France

A harmonic RF system for bunch lengthening to increase the Touschek lifetime of the ESRF Extemely Brilliant Source (EBS) is under study. Multiparticle simulations have been performed to study the bunch lengthening and the bunch shape with impedance effect and with third or fourth harmonic cavities. The effect of a harmonic RF system on the microwave instability is studied, finding an increase in the threshold. The AC Robinson instability threshold with a superconducting harmonic cavity has been studied with multiparticle simulations.

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THPAB005

Improvement of the Analytic Vlasov Solver DELPHI

3688

D. Amorim
Université Grenoble Alpes, Grenoble, France
N. Biancacci, K.S.B. Li, E. Métral
CERN, Geneva, Switzerland

The simulation code DELPHI is an analytic Vlasov solver which allows to evaluate the beam transverse stability with respect to impedance effects. It allows to perform fast scans over parameters such as chromaticity, damper gain or beam intensity for a given impedance model and particle distribution. In order to improve the simulation code, new longitudinal particle distributions have been implemented. The simulations results obtained with these distributions are compared to theoretical predictions. An additional post-processing of DELPHI's output has also been implemented, allowing to reconstruct the signal seen by head-tail stripline monitors, in particular in presence of bunch-by-bunch damper. The results are compared to theoretical models, to pyHEADTAIL simulations and to measurements performed in the LHC.

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THPAB006

Nuage, Ion Cloud Tracker

3692

SUSPSIK054

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A. Gamelin, C. Bruni, D. Radevych
LAL, Orsay, France

Funding: Work is supported by ANR-10-EQPX-51, by grants from Région Ile-de- France, IN2P3 and Pheniics Doctoral School.
NUAGE is a data parallel Matlab code which simulates the ion cloud effect in electron storage rings. The ion cloud is tracked in the ring taking into account the transverse and longitudinal effect of the beam-ion interaction, tracking in magnetic elements, usage of electrodes and gaps as clearing means. This program has been used to compute ionised ion equilibrium state and its neutralisation factor. In this article the NUAGE code is presented. The model, analysis method and performances are discussed.

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THPAB007

Short Bunches at the Transition From Strong to Weak Longitudinal Instability

3696

P. Kuske
HZB, Berlin, Germany

The interaction of particles with their vacuum sur-roundings can lead to longitudinal instabilities of the whole bunch of particles. Most of these instabilities are strong and the growth rates are large compared to the damping rate. For a weak instability the opposite is true and with just a resistive impedance the instability would always be weak and independent of the bunch length. The interaction of a bunch with its own radiation emitted midway between parallel plates leads to a strong instabil-ity for long bunches and a transition to weak instability if the bunch length becomes shorter. This regime is ana-lysed numerically with a Vlasov-Fokker-Planck solver. The results are compared to recent observations at ANKA. An attempt is made to explain the remaining discrepan-cies by including higher order terms of the momentum compaction factor into these calculations. There are indi-cations that the simple model needs refinements in order to take radiation from upstream dipoles into account.

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THPAB014

An Adaptive Mesh-Based Method for the Efficient Simulation of LSC-Driven Microbunching Gain in FEL Applications

3720

Ph. Amstutz
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
M. Vogt
DESY, Hamburg, Germany

Electron beams with high peak current as they are required for the operation of free-electron lasers (FELs) are often generated by means of a series of magnetic bunch compressors. In conjunction with a collective coherent force, e.g. longitudinal space-charge (LSC), bunch compressors can possibly cause a wavelength dependent amplification of initial density inhomogeneities, potentially to an extent detrimental to the operation of the FEL. A common model, consisting of LSC, acceleration (kicks), and magnetic chicanes (drift-type maps), is governed by a time-discrete Vlasov-Poisson system. Such systems have been successfully simulated using mesh based representations of the phase space density (PSD) and the method of characteristics for the update step. However, for the irregular and exotic PSDs, prevalent in FEL applications, a homogeneous high resolution discretization on a naive rectangular mesh can be prohibitively wasteful. Here we present an approach based on adaptive tree refinement that addresses the complexity of the PSDs and allows for the efficient simulation of LSC-driven micro-bunching in FELs.

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THPAB020

Coupling Impedances and Collective Effects for FCC-ee

3734

E. Belli, M. Migliorati
University of Rome La Sapienza, Rome, Italy
G. Castorina, B. Spataro, M. Zobov
INFN/LNF, Frascati (Roma), Italy
A. Novokhatski
SLAC, Menlo Park, California, USA
S. Persichelli
LBNL, Berkeley, California, USA

A very important issue for the Future Circular Collider (FCC) is represented by collective effects due to the self-induced electromagnetic fields, which, acting back on the beam, could produce dangerous instabilities. In this paper we will focus our work on the FCC electron-positron machine: in particular we will study some important sources of wake fields, their coupling impedances and the impact on the beam dynamics. We will also discuss longitudinal and transverse instability thresholds, both for single bunch and multibunch, and indicate some ways to mitigate such instabilities.

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THPAB025

Simulation Studies of Transverse Beam Instabilities and Measures Beyond 1 MW Beam Power in the 3-GeV RCS of J-PARC

3750

P.K. Saha, H. Hotchi, Y. Shobuda
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan

The transverse impedance of the extraction kicker magnets is a significant beam instability source in the 3-GeV RCS (Rapid Cycling Synchrotron) of J-PARC (Japan Proton Accelerator Research Complex). The systematic simulation studies for beam instability by including the space charge effect has been done by using the ORBIT code. The simulation results are well reproduced in the corresponding measurements. The designed 1 MW beam power has recently been accomplished by keeping sextuple magnets off in order to stabilize the beam by utilizing the large lattice chromaticity throughout the entire acceleration period. The RCS simultaneously delivers extracted beam to the MLF (Material and Life Science Experimental Facility) and the MR (Main Ring). In order to ensure 1 MW beam power at the MLF even when RCS beam sharing to the MR is twice increased as well as when a second target station is constructed at the MLF, a beam power of 1.5 MW has to be realized in the RCS. However, the simulation shows that beyond 1 MW the beam is unstable even if no chromaticity is corrected. A reduction of the kicker impedance by at least a half is required in order to achieve 1.5 MW beam power in the RCS.

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THPAB026

Feasibility Analysis of Emittance Preservation During Bunch Compression in the Presence of Coherent Synchrotron Radiation in an Arc

3753

SUSPSIK055

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X.Y. Huang, X. Cui, S. Gu, Y. Jiao, G. Xu
IHEP, Beijing, People's Republic of China

Electron beam with low transverse emittance, short bunch length and high peak current is the basic requirement in modern high-brightness light sources. However, coherent synchrotron radiation (CSR) will dilute the transverse emittance when the electron beams pass through a magnetic bunch compressor and degrade the performance of the machine. In this paper, based on our CSR point-kick analysis, arc compressors with high compression factor in the presence of CSR effect are studied, both periodic and aperiodic arcs are included. Through analytical and numerical research, an easy optics design technique is introduced to minimize the emittance dilution within these compressors. Taking practical considerations into account, the results of periodic and aperiodic arcs are compared.

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THPAB029

Simulation of the Single Bunch Instabilities for the High Energy Photon Source

3760

Z. Duan, N. Wang, H.S. Xu
IHEP, Beijing, People's Republic of China

Funding: Work supported by Natural Science Foundation of China (No.11605212).
Timing modes pursing a large single bunch charge will be important operation modes for the green-field High Energy Photon Source (HEPS). The single bunch instabilities are simulated with the elegant tracking code, based on the current impedance budget. In particular, a novel on-axis accumulation scheme* based on the RF gymnastics of an active double-RF system was proposed as a candidate injection scheme for HEPS, while the zero-current rms bunch length dramatically decreases during the injection, from 32 mm to 3 mm, over a time duration of about 200 ms. The single bunch instabilities are evaluated for both the operation mode with optimal bunch lengthening as well as the injection mode with the very short bunch length, as a first step in understanding the possible beam instability for this injection scheme.
* G. Xu, et al., in Proc. IPAC'16, pp. 2886-2888. Z. Duan, et al., in Proc. eeFACT 2016.

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THPAB030

Studies on Collective Instabilities in HEPS

3763

N. Wang, Z. Duan, C. Li, S.K. Tian, H.S. Xu
IHEP, Beijing, People's Republic of China

The High Energy Photon Source (HEPS) is a new designed photon source at beam energy of 6 GeV. Due to the small beam size and increased coupling impedance with the restricted beam pipe aperture, the collective effects may bring new challenges to the physical design of the machine. The collective instabilities are estimated for different operation mode. The critical instability issues are also identified for each mode.

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THPAB031

Study of Beam Break Up in Irradiation Linacs

3767

SUSPSIK056

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X.C. Meng, H.B. Chen, W. Gai, J. Shi, S.X. Zheng
TUB, Beijing, People's Republic of China
G.H. Li, J.S. Liu, Y.H. Liu
NUCTECH, Beijing, People's Republic of China
F.H. de Sá
LNLS, Campinas, Brazil

Many recent experiments of the irradiation linacs produced at Tsinghua University indicate that beam power is limited by beam break up (BBU). Limits exist while the beam current or the pulse width is increased. In this paper, we illustrate the bream break up (BBU) phenomenon in the cases of both the 10MeV travelling-wave linac and 10MeV backward travelling-wave linac. The higher order modes in the linacs are analysed and the wake fields are calculated both with theoretical analysis and numerical simulation. Also, the beam dynamics is studied on the basis of the wakefield results to find a BBU threshold in these structures.

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THPAB032

Estimates of Collective Effects in the HALS Storage Ring Having the First Version Lattice

3770

SUSPSIK057

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N. Hu, Z.H. Bai, W. Li, Q. Luo, L. Wang
USTC/NSRL, Hefei, Anhui, People's Republic of China

The Hefei Advanced Light Source (HALS) is a diffraction-limited storage ring with a beam energy of 2.0 GeV. Recently the first version lattice has been designed for the HALS storage ring, and the natural emittance is about 18 pm·rad. In this paper, we study the collective effects in this storage ring, including calculations of intra-beam scattering effect and Touschek lifetime, and estimates of the thresholds of some single-bunch and multi-bunch instabilities.

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THPAB040

Destabilising Effect of Linear Coupling in the LHC

3791

L.R. Carver, D. Amorim, N. Biancacci, X. Buffat, K.S.B. Li, E. Métral, B. Salvant, M. Schenk
CERN, Geneva, Switzerland

During operation in 2015 and 2016, some transverse instabilities were observed when either the coupling (or closest tune approach) C- was large, or when the tunes were moved closer together. This motivated a campaign of simulations on the effect of linear coupling on the transverse stability. Measurements made during operation and with dedicated beam time have been found to confirm the predictions. This paper will detail the results of the linear coupling studies and relate them to operation of the LHC in the future.

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THPAB053

Laser Heater Deisgn for the CLARA FEL Test Facility

3833

A.D. Brynes, S.P. Jamison, B.D. Muratori, N. Thompson, P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
S.P. Jamison, B.D. Muratori, N. Thompson, P.H. Williams
Cockcroft Institute, Warrington, Cheshire, United Kingdom

We present considerations of microbunching studies in the CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility under construction at Daresbury Laboratory. CLARA, a high-brightness electron linac, presents an opportunity to study the microbunching instability. A number of theoretical models have been proposed concerning the causes of this instability, and it has also been observed at various FEL facilities. We have applied these models to the CLARA FEL, and propose a suitable laser heater design which will provide flexibility in terms of the range of modes of operation for CLARA. We also propose a method for inducing and controlling the microbunching instability via pulse stacking of the photoinjector laser.

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THPAB059

CSR and Space Charge Studies for the CLARA Phase 1 Beamline

3851

B.S. Kyle, R.B. Appleby
UMAN, Manchester, United Kingdom
J.K. Jones, P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
M.J. de Loos, S.B. van der Geer
Pulsar Physics, Eindhoven, The Netherlands

The installation of Phase 1 of CLARA, the UK's new FEL test facility, is currently underway at Daresbury Laboratory. When completed, it will be able to deliver 45 MeV electron beams to the pre-existing VELA beamline, which runs parallel. Phase 1 consists of a 10 Hz photocathode gun, a 2 m long S-band travelling wave linac, a spectrometer line, and associated optics and diagnostics. A detailed study into the beam dynamics of the lattice is presented, with a focus towards the effects of space charge and coherent synchrotron radiation on the electron bunch. Simulations disagreed with predictions from a one-dimensional model of coherent radiation, and this disagreement is believed to be due to a violation of the Derbenev criterion.

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THPAB076

Coherent Synchrotron Radiation Simulations for Off-Axis Beams Using the Bmad Toolkit

3887

D. Sagan, C.E. Mayes
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Coherent synchrotron radiation (CSR) potentially limits operation accelerators with high bunch charges and/or short bunch lengths by increasing energy spread, and by Except at the lowest beam energies, the one dimensional treatment of coherent synchrotron radiation (CSR) originally developed by Saldin is an efficient and reasonably accurate way to simulate the effects of CSR on a particle beam. A possible problem with standard implementations of the 1D CSR formalism is that these implementations assume that the beam centroid is close to the reference trajectory that defines the lattice. In this paper, the one dimensional treatment is extended to take into account beams whose centroid is far from the reference trajectory and an example using the Cornell-BNL Fixed Field Alternating Gradient (FFAG) accelerator CBETA is given.

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THPAB078

Beam Dynamics Studies of the Transverse Gradient Undulator and Its Application to Suppression of Microbunching Instability

3895

T. Liu, Y. Ding, Z. Huang, W. Qin
SLAC, Menlo Park, California, USA
T. Liu
University of Chinese Academy of Sciences, Beijing, People's Republic of China
T. Liu, D. Wang
SINAP, Shanghai, People's Republic of China

A transverse gradient undulator (TGU) which was initially proposed for high gain free electron lasers (FELs) driven by electron beams with relatively large energy spread, can be extended to the application of beam dynamics, such as phase-merging enhanced harmonic generation FEL and suppression of microbunching instability. In this contribution we present beam dynamics studies of the TGU, analyze the resulting focusing and dispersion, and discuss the effects of an additional corrector on the TGU. As an application to beam dynamics, we show a feasible transport system based on the TGU as a reversible electron beam heater to suppress the microbunching instability of the electron beam.

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THPAB080

Estimations of Coherent Instabilities for JLEIC

3903

R. Li
JLab, Newport News, Virginia, USA

Funding: Work supported by the Department of Energy, Laboratory Directed Research and Development Funding, under Contract No. DE-AC05-06OR23177
JLEIC is the medium energy electron-ion collider currently under active design at Jefferson Lab*. The design goals of JLEIC are both high luminosity (1033-1034 cm^-2ses⁻¹) and high polarization (>70%) for the electron and light ion beams, for a wide range of electron and ion beam energies and for a wide spectrum of ion species. The unprecedented luminosity goal for this electron-ion collider sets strong requirements for the understanding and management of potential collective effects in JLEIC. In this paper, we present preliminary estimations of single and coupled bunch coherent instabilities for the electron and proton beams at collision energies for the JLEIC design. Further improvement of the estimations and mitigation methods are discussed.
* MEIC design summary, http://arxiv.org/ftp/arxiv/papers/1504/1504.07961.pdf, (2015).

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THPVA010

Electron Cloud Simulations for the Main Ring of J-PARC

4436

B. Yee-Rendón, R. Muto, K. Ohmi, K. Satou, M. Tomizawa, T. Toyama
KEK, Ibaraki, Japan

The simulation of beam instabilities is a helpful tool to evaluate potential threats against the machine protection of the high intensity beams. At Main Ring (MR) of J-PARC, signals related to the electron cloud have been observed during the slow beam extraction mode. Hence, several studies were conducted to investigate the mechanism that produces it, the results confirmed a strong dependence on the beam intensity and the bunch structure in the formation of the electron cloud, however, the precise explanation of its trigger conditions remains incomplete. To shed light on the problem, electron cloud simulations were done using an updated version of the computational model developed from previous works at KEK. The code employed the signals of the measurements to reproduce the events seen during the surveys.

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THPVA084

Evaluation of Collective Effects in Iranian Light Source Facility (ILSF) Storage Ring

4650

E. Ahmadi, S. Ahmadiannamin, J. Rahighi
ILSF, Tehran, Iran
S.M. Jazayeri
IUST, Narmac, Tehran, Iran

In this paper, we present the calculations of various collective effects in the storage ring of ILSF, a synchrotron light source under design in Iran. The ILSF storage ring is based on 5-BA lattice structure and emittance of 270 pm-rad which is optimized to provide high brightness and flux photons for the users. Because of design features, small radius vacuum pipe and small momentum compaction factor of lattice, it is expected that instabilities emerging from collective effects will affect significantly the beam quality and make it is challenging to reach maximum designed beam current. We will address the results of beam quality degradation and threshold calculations for different singlebunch and multibunch instabilities.

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THPVA143

Beam-Breakup Studies for the 4-Pass Cornell-Brookhaven Energy Recovery LINAC Test Accelerator

4801

W. Lou, J.A. Crittenden, G.H. Hoffstaetter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Cornell University and Brookhaven National Laboratory are currently designing the Cornell-BNL ERL Test Accelerator (CBETA). To be built at Cornell's Wilson Lab, CBETA utilizes the existing ERL injector and main linac cryomodule (MLC). As the electron bunches pass through the MLC cavities, higher order modes (HOMs) are excited. The recirculating bunches interact with the HOMs, which can give rise to beam-breakup instability (BBU). Here we present simulation results on how BBU limits the maximum achievable current, and potential ways to improve the threshold current.

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