IPAC2021 - Classification: MC5: Beam Dynamics and EM Fields / D05 Coherent and Incoherent Instabilities

Paper	Title	Page
MOPAB056	Optimization of a TBA with Stable Optics and Minimal Longitudinal Dispersion and CSR-Induced Emittance Growth	241
	C. Zhang, Y. Jiao IHEP, Beijing, People’s Republic of China C.-Y. Tsai HUST, Wuhan, People’s Republic of China
	Funding: National Natural Science Foundation of China (No. 11922512), Youth Innovation Promotion Association of Chinese Academy of Sciences (No. Y201904), National Key R&D Program of China (No. 2016YFA0401900) In the beam transfer line which often consists of dipoles to deflect the beam trajectory, longitudinal dispersion effect and emission of coherent synchrotron radiation (CSR) will lead to beam phase space distortion, thus degrading the machine performance. In this study, optimizations of a triple-bend achromat (TBA) cell are conducted using the multi-objective particle swarm optimization (MOPSO) method to suppress the CSR-induced emittance growth and minimize the longitudinal dispersion functions up to high orders, simultaneously. For the longitudinal dispersion function, results of three optimization settings are reported, which makes the TBA design first-order, second-order, and higher-order isochronous. Furthermore, we study the shortest possible beamline length of the higher-order isochronous TBA design, which may pave the way to designing a more compact beam transfer line.
	Poster MOPAB056 [0.366 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB056
About •	paper received ※ 12 May 2021 paper accepted ※ 28 May 2021 issue date ※ 15 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPAB069	Equilibrium Bunch Density Distribution with Multiple Active and Passive RF Cavities	278
	A. Gamelin SOLEIL, Gif-sur-Yvette, France N. Yamamoto KEK, Ibaraki, Japan
	This paper describes a method to get the equilibrium bunch density distribution with an arbitrary number of active or passive RF cavities in uniform filling. This method is an extension of the one presented by M. Venturini which assumes a passive harmonic cavity and no beam loading in the main RF cavity. M. Venturini, "Passive higher-harmonic rf cavities with general settings and multibunch instabilities in electron storage rings," Physical Review Accelerators and Beams, 2018.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB069
About •	paper received ※ 17 May 2021 paper accepted ※ 23 June 2021 issue date ※ 23 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUXA01	Advances in Understanding of Ion Effects in Electron Storage Rings	1267
	J.R. Calvey, M. Borland, T.K. Clute, J.C. Dooling, L. Emery, J. Gagliano, J.E. Hoyt, P.S. Kallakuri ANL, Lemont, Illinois, USA
	Ion instability, in which beam motion couples with trapped ions in an accelerator, is a serious concern for high-brightness electron storage rings. For the APS-Upgrade, we plan to mitigate coherent ion instability using a compensated gap scheme. To study incoherent effects (such as emittance growth), an IONEFFECTS element has been incorporated into the particle tracking code ELEGANT. The simulations include multiple ionization, transverse impedance, and charge variation between bunches. Once these effects are included, the simulations show good agreement with measurements at the present APS. We have also installed a gas injection system, which creates a controlled pressure bump of Nitrogen gas in a short section of the APS ring. The resulting ion instability was studied under a wide variety of beam conditions. For cases with no or insufficient train gaps, large emittance growth was observed. IONEFFECTS simulations of the gas injection experiment and APS-U storage ring show the possibility of runaway emittance blowup, where the blown-up beam traps more ions, driving further instability.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA01
About •	paper received ※ 24 June 2021 paper accepted ※ 27 July 2021 issue date ※ 10 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUXA06	Loss of Transverse Landau Damping by Diffusion in High-Energy Hadron Colliders	1286
	S.V. Furuseth, X. Buffat CERN, Geneva, Switzerland S.V. Furuseth EPFL, Lausanne, Switzerland
	Circular hadron colliders rely on Landau damping to stabilize the beams. Landau damping depends strongly on the bunch distribution, which is often assumed to be Gaussian in the transverse planes. In this paper, we introduce and explain an instability mechanism observed in the LHC, where Landau damping is eventually lost due to a diffusion that modifies the transverse bunch distribution. The mechanism is caused by a wide-spectrum noise that excites the transverse motion of the beam, which consequently produces wakefields that drive a narrow-spectrum diffusion. It is shown that this diffusion efficiently lowers the stability diagram at the frequency of the least stable coherent mode, leading to a loss of Landau damping after a latency. A semi-analytical model agrees with measurements in dedicated latency experiments performed in the LHC. This instability mechanism explains the need for a stability margin in octupole current in the LHC, relative to the amount needed to stabilize a Gaussian beam. We detail the impact of this mechanism and possible mitigations for the LHC and HL-LHC.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA06
About •	paper received ※ 19 May 2021 paper accepted ※ 25 June 2021 issue date ※ 10 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPAB254	Limiting Coherent Longitudinal Beam Oscillations in the EIC Electron Storage Ring	2046
	B. Podobedov Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA M. Blaskiewicz 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. We study coherent longitudinal beam oscillations in the EIC electron storage ring (ESR). We show that to avoid unacceptable hadron emittance growth due to finite crossing angle, the amplitude of these oscillations needs to be limited to a fraction of a millimeter. Using an analytical model we estimate the amplitude of these oscillations under the two scenarios: 1) the beam is passively stable and the oscillations are driven by RF phase noise only; 2) a coupled-bunch instability, presently expected in the ESR, is damped by a longitudinal feedback system. We show that, for the 2nd scenario, comfortable specifications for RF phase noise and feedback sensor noise will be sufficient to maintain the oscillation amplitude within the required limits.
	Poster TUPAB254 [1.347 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB254
About •	paper received ※ 12 May 2021 paper accepted ※ 18 June 2021 issue date ※ 26 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB082	Single Bunch Instability Simulations in the Storage Ring of the ALS-U Project	2783
	D. Wang, K.L.F. Bane, S. De Santis, M.P. Ehrlichman, D. Li, T.H. Luo, O. Omolayo, G. Penn, C. Steier, M. Venturini LBNL, Berkeley, California, USA
	As the broad-band impedance modeling and the vacuum chamber design of the new Advanced Light Source storage ring (ALS- U) reach maturity, we report on progress in single-bunch collective effects studies. A pseudo-Green function wake representing the entire ring was earlier obtained by numerical and analytical methods. Macroparticle simulations using the computer code "elegant" and this wake function are used to determine the instability thresholds for longitudinal and transverse motion. We consider various operating conditions, such as without/with higher-harmonic RF cavities, zero/finite linear chromaticity, and without/with a transverse bunch-by-bunch feedback system. Results show enough margin for the broadband impedance budget when the single-bunch instability thresholds are compared with the design bunch charge.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB082
About •	paper received ※ 20 May 2021 paper accepted ※ 01 July 2021 issue date ※ 12 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB150	Monotron Beam Break Up Instability Analysis	2968
	V. Volkov, V.M. Petrov BINP SB RAS, Novosibirsk, Russia
	New features of monotron beam break up (BBU) instability such as the typing of high order monopole modes (HOMs)in each cavity by two classes one of them are stable and other ones are unstable, HOM effective quality factor depending on average beam current, and normalized invariable threshold current individually characterizes each HOM are investigated in this article in detail.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB150
About •	paper received ※ 19 May 2021 paper accepted ※ 09 June 2021 issue date ※ 31 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB151	Regenerative Beam Break Up Instability Analysis	2971
	V. Volkov, V.M. Petrov BINP SB RAS, Novosibirsk, Russia
	New features of regenerative beam break up (BBU) instability such as the typing of high order dipole modes (HOMs)in each cavity by two classes, one of them are stable and other ones are unstable, HOM effective quality factor depending on average beam current, and normalized invariable threshold current individually characterizes each HOM are investigated in this article in detail.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB151
About •	paper received ※ 19 May 2021 paper accepted ※ 22 June 2021 issue date ※ 01 September 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB226	Investigation of Vlasov Systems with a Certain Class of Linearly-Collective Hamiltonians	3157
	Ph. Amstutz, M. Vogt DESY, Hamburg, Germany
	In many cases the Vlasov equation cannot be solved exactly due its inherent non-linearity arising from collective terms in the Hamiltonian. Based on the analysis of the Hamiltonian’s dependence on the phase-space density and the requirement for self-consistency in this contribution a class of Hamiltonians is defined and characterized. For members of this class the corresponding expansion of the Vlasov equation terminates. The new, potentially non-autonomous, Hamiltonian of the resulting Liouville equation depends only on the initial condition of the phase-space density. Prominent members of this class are Poisson-type kick-Hamiltonians, which we show as an example. We expect these investigations to be a potential starting point for the analysis and conception of operator-splitting schemes or splitting-free methods for beam-dynamics simulation codes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB226
About •	paper received ※ 18 May 2021 paper accepted ※ 01 July 2021 issue date ※ 17 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB227	Mechanism of Longitudinal Single-Bunch Instability in the CERN SPS	3161
	I. Karpov CERN, Meyrin, Switzerland M. Gadioux UCD, Dublin, Ireland
	Understanding the origin of beam instabilities is essential for reaching the highest performance of proton synchrotrons. In the present work, the Oide-Yokoya eigenvalue method of solving the linearised Vlasov equation was used to shed light on the mechanism of longitudinal single-bunch instability in the CERN SPS. In particular, semi-analytical calculations were done for the full longitudinal impedance model, taking into account the RF nonlinearity. The obtained results agree well with macro-particle simulations and are consistent with available beam measurements. For the first time, the instability has been interpreted as a coupling of radial modes within a single azimuthal mode, due to a strong potential-well distortion of the synchrotron-frequency distribution. To avoid this instability, a higher RF voltage is required at a given emittance. Thus, the instability mechanism is very different from the loss of Landau damping, which, in contrast, is mitigated by a lower RF voltage. This understanding also allowed us to optimise the RF voltage programmes during the acceleration cycle for high-intensity bunches used in the AWAKE experiment at CERN.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB227
About •	paper received ※ 12 May 2021 paper accepted ※ 01 July 2021 issue date ※ 15 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB228	Modelling and Counteracting Microbunching Instability in Spreader Lines of Radiofrequency and Plasma-Based Accelerators for Free-Electron Lasers	3165
	G. Perosa Università degli Studi di Trieste, Trieste, Italy S. Di Mitri Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	High energy radiofrequency and plasma-driven accelerators target electron beam brightness suitable for x-ray free-electron lasers. Microbunching instability can be enhanced during beam transport through the spreader line from the accelerator to the undulator, degrading the brightness of the accelerated beam and therefore reducing the lasing efficiency. We present a semi-analytical model of the instability, benchmarked with experimental data at the FERMI free-electron laser, in the presence of intrabeam scattering and beam heating. Strategies for minimization of the instability both in conventional and plasma-based accelerators are discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB228
About •	paper received ※ 19 May 2021 paper accepted ※ 08 July 2021 issue date ※ 02 September 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB229	Transverse Density Pileup and Pattern Formation in Dense Ultracold Electron Beamlets under Coulomb Expansion	3169
	A.J. Tencate, K. Bhuyan, B. Erdélyi Northern Illinois University, DeKalb, Illinois, USA
	Funding: This work was sponsored by the US Department of Energy Office of Science under Grant DE-SC0020241. Dynamic Coulomb expansion of dense particle bunches can lead to transverse density shock-like propagation for nonuniform bunch distributions. Furthermore, under favorable circumstances, multiple bunches in close proximity can collide without crossing to form wheel-and-spoke patterns. This process has been observed experimentally for Rubidium ions, but not yet for electrons, where the dynamics occur over far shorter length scales. We simulate the interaction of electron bunches while varying the initial transverse temperature and density profiles to determine the thresholds that characterize this pattern formation. Additionally, we consider the effects of asymmetries and the impact of a low-density halo on the overall process. The simulations are conducted using a novel high-fidelity algorithm for collisional particle dynamics.
	Poster WEPAB229 [7.411 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB229
About •	paper received ※ 19 May 2021 paper accepted ※ 02 July 2021 issue date ※ 13 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB233	Excitation of Micro-Bunching in Short Electron Bunches Using RF Amplitude Modulation	3173
	T. Boltz, E. Blomley, M. Brosi, E. Bründermann, B. Härer, A. Mochihashi, A.-S. Müller, P. Schreiber, M. Schuh, M. Yan KIT, Karlsruhe, Germany
	In its short-bunch operation mode, the KIT storage ring KARA provides picosecond-long electron bunches, which emit coherent synchrotron radiation (CSR) up to the terahertz frequency range. Due to the high spatial compression under these conditions, the self-interaction of the bunch with its own emitted CSR induces a wake-field, which significantly influences the longitudinal charge distribution. Above a given threshold current, this leads to the formation of dynamically evolving micro-structures within the bunch and is thus called micro-bunching instability. As CSR is emitted at wavelengths corresponding to the spatial dimension of the emitter, these small structures lead to an increased emission of CSR at higher frequencies. The instability is therefore deliberately induced at KARA to provide intense THz radiation to dedicated experiments. To further increase the emitted power in the desired frequency range, we consider the potential of RF amplitude modulations to intentionally excite this form of micro-bunching in short electron bunches. This work is supported by the BMBF project 05K19VKC TiMo (Federal Ministry of Education and Research).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB233
About •	paper received ※ 19 May 2021 paper accepted ※ 01 July 2021 issue date ※ 17 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB234	Simulating Two Dimensional Coherent Synchrotron Radiation in Python	3177
	W. Lou, Y. Cai, C.E. Mayes, G.R. White SLAC, Menlo Park, California, USA
	Coherent Synchrotron Radiation (CSR) in bending magnets poses an important limit for electron beams to reach high brightness in novel accelerators. While the longitudinal wakefield has been well studied in one-dimensional CSR theory and implemented in various simulation codes, transverse wakefields have received less attention. Following the recently developed two-dimensional CSR theory, we developed a Python code simulating the steady-state two-dimensional CSR effects. The computed CSR wakes have been benchmarked with theory and other simulation codes. To speed up computation speed, the code applies vectorization, parallel processing, and Numba in Python.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB234
About •	paper received ※ 20 May 2021 paper accepted ※ 01 July 2021 issue date ※ 20 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB235	TMCI Theory of Flat Chambers Revisited	3181
	T.F. Günzel ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
	By accounting for the transverse impedance’ quadrupolar component according to the work of R.Lindberg , no TMCI-instability can be observed in case of a pure horizontal resistive wall impedance of flat vacuum chambers. In order to study this effect more closely, TMCI-theory is reviewed and Lindberg’s work is further developed by including the resonator model as impedance type. The theory is applied to the ALBA-impedance model for the calculation of horizontal TMCI-detuning and threshold. Moreover, a couple of example cases are presented including vertical TMCI-detuning and threshold. Results on both planes are compared to simpler descriptions which account for the quadrupolar impedance effect only by tune shift. Ryan Lindberg, Fokker-Planck analysis of transverse collective instabilities in electron storage rings, Phy. Rev. Acc. Beams 19, 124402 (2016)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB235
About •	paper received ※ 19 May 2021 paper accepted ※ 01 July 2021 issue date ※ 19 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB238	Modeling Short Range Wakefield Effects in a High Gradient Linac	3185
	F. Bosco, M. Carillo, L. Faillace, L. Giuliano, M. Migliorati, A. Mostacci, L. Palumbo Sapienza University of Rome, Rome, Italy M. Behtouei, L. Faillace, A. Giribono, B. Spataro, C. Vaccarezza INFN/LNF, Frascati, Italy F. Bosco, M. Migliorati INFN-Roma1, Rome, Italy L. Giuliano, A. Mostacci, L. Palumbo INFN-Roma, Roma, Italy J.B. Rosenzweig UCLA, Los Angeles, California, USA
	Funding: This work is supported by DARPA GRIT under contract no. 20204571 and partially by INFN National committee V through the ARYA project. The interaction of charged beams with the surrounding accelerating structures requires a thorough investigation due to potential negative effects on the phase space quality. Indeed, the wakefields acting back on the beam are responsible for emittance dilution and instabilities, such as the beam break-up, which limit the performances of electron-based radiation sources and linear colliders. Here we introduce a new tracking code which is meant to investigate the effects of short-range transverse wakefields in linear accelerators. The tracking is based on quasi-analytical models for the beam dynamics which, in addition to the basic optics specified by the applied fields, include dipole wakefield forces and a simple approach to account for space-charge effects. Such features provide a reliable tool which easily allows to inspect the performances of a linac. To validate the model, a parallel analysis for a reference case is performed with well-known beam dynamics codes, and comparisons are shown. As an illustrative application, we discuss a study on alignment tolerances evaluating the emittance growth induced by misaligned accelerating sections.
	Poster WEPAB238 [1.747 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB238
About •	paper received ※ 18 May 2021 paper accepted ※ 07 July 2021 issue date ※ 01 September 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THXA04	Microbunching Instability in the Presence of Intrabeam Scattering for Single-Pass Accelerators	3692
	C.-Y. Tsai HUST, Wuhan, People’s Republic of China W. Qin Lund University, Lund, Sweden
	Funding: This work is supported by the Fundamental Research Funds for the Central Universities under Project No. 5003131049 and National Natural Science Foundation of China under project No. 11905073. Intrabeam scattering (IBS) has long been studied in lepton or hadron storage rings as a slow diffusion process, while the effects of IBS on single-pass or recirculating electron accelerators have drawn attention only in the recent two decades due to the emergence of linac-based or ERL-based 4th-generation light sources, which require high-quality electron beams during the beam transport. Recent experimental measurements indicate that in some parameter regimes, IBS can have a significant influence on microbunched beam dynamics. Here we develop a theoretical formulation* of microbunching instability (MBI) in the presence of IBS for single-pass accelerators. We start from the Vlasov-Fokker-Planck (VFP) equation, combining both collective longitudinal space charge and incoherent IBS effects. The linearized VFP equation with the corresponding coefficients is derived. The evolutions of the phase space density and energy modulations are formulated as a set of coupled integral equations. The formulation** is then applied to a simplified single-pass transport line. The results from the semi-analytical calculation are compared and show good agreement with particle tracking simulations. * C.-Y. Tsai et al., Phys. Rev. Accel. Beams 23, 124401 (2020) ** C.-Y. Tsai and W. Q, Phys. Plasmas (2021), accepted for publication
	Slides THXA04 [2.699 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXA04
About •	paper received ※ 13 May 2021 paper accepted ※ 19 July 2021 issue date ※ 13 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THXA05	A Fast Method of 2D Calculation of Coherent Synchrotron Radiation Wakefield in Relativistic Beams	3696
	J. Tang, Z. Huang, G. Stupakov SLAC, Menlo Park, California, USA
	Coherent Synchrotron Radiation (CSR) is regarded as one of the most important reasons that limit beam brightness in modern accelerators. CSR wakefield is often computed in a 1D assuming a line charge, which can become invalid when the beam has a large transverse extension and small bunch length. On the other hand, the existing 2D or 3D codes are often computationally inefficient or incomplete. In our previous work * we developed a new model for fast computation of 2D CSR wakefield in relativistic beams with Gaussian distribution. Here we further generalize this model to achieve self-consistent computation compatible with arbitrary beam distribution and nonlinear magnetic lattice with particle tracking. These new features can enable us to perform realistic simulations and study the physics of CSR beyond 1D in electron beams with extreme short bunch length and high peak current. * J. Tang and G. Stupakov. NAPAC2019, paper WEPLS09 (2019).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXA05
About •	paper received ※ 19 May 2021 paper accepted ※ 20 July 2021 issue date ※ 21 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPAB076	Effects of Chromaticity and Synchrotron Emission on Coupled-Bunch Transverse Stability	3937
	R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. We present a theory that can compute the transverse coupled-bunch instability growth rates at any chromaticity and for any longitudinal potential provided only that the long-range wakefield varies slowly over the bunch. The theory is expressed in terms of the usual coupled-bunch eigenvalues at zero chromaticity, and when the longitudinal motion is simple harmonic our solution only requires numerical root-finding that is easy to implement and fast to solve; the more general case requires some additional calculations but is still relatively fast. The theory predicts that the coupled-bunch growth rates can be significantly reduced when the chromatic betatron tune spread is larger than the coupled-bunch growth rate at zero chromaticity. Our theoretical results are compared favorably with tracking simulations for the long-range resistive wall instability, and we also indicate how damping and diffusion from synchrotron emission can further reduce or even stabilize the dynamics.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB076
About •	paper received ※ 20 May 2021 paper accepted ※ 26 July 2021 issue date ※ 26 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Optimization of a TBA with Stable Optics and Minimal Longitudinal Dispersion and CSR-Induced Emittance Growth

241

C. Zhang, Y. Jiao
IHEP, Beijing, People’s Republic of China
C.-Y. Tsai
HUST, Wuhan, People’s Republic of China

Funding: National Natural Science Foundation of China (No. 11922512), Youth Innovation Promotion Association of Chinese Academy of Sciences (No. Y201904), National Key R&D Program of China (No. 2016YFA0401900)
In the beam transfer line which often consists of dipoles to deflect the beam trajectory, longitudinal dispersion effect and emission of coherent synchrotron radiation (CSR) will lead to beam phase space distortion, thus degrading the machine performance. In this study, optimizations of a triple-bend achromat (TBA) cell are conducted using the multi-objective particle swarm optimization (MOPSO) method to suppress the CSR-induced emittance growth and minimize the longitudinal dispersion functions up to high orders, simultaneously. For the longitudinal dispersion function, results of three optimization settings are reported, which makes the TBA design first-order, second-order, and higher-order isochronous. Furthermore, we study the shortest possible beamline length of the higher-order isochronous TBA design, which may pave the way to designing a more compact beam transfer line.

Poster MOPAB056 [0.366 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB056

About •

paper received ※ 12 May 2021 paper accepted ※ 28 May 2021 issue date ※ 15 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPAB069

Equilibrium Bunch Density Distribution with Multiple Active and Passive RF Cavities

278

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

This paper describes a method to get the equilibrium bunch density distribution with an arbitrary number of active or passive RF cavities in uniform filling. This method is an extension of the one presented by M. Venturini which assumes a passive harmonic cavity and no beam loading in the main RF cavity*.
*M. Venturini, "Passive higher-harmonic rf cavities with general settings and multibunch instabilities in electron storage rings," Physical Review Accelerators and Beams, 2018.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB069

About •

paper received ※ 17 May 2021 paper accepted ※ 23 June 2021 issue date ※ 23 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUXA01

Advances in Understanding of Ion Effects in Electron Storage Rings

1267

J.R. Calvey, M. Borland, T.K. Clute, J.C. Dooling, L. Emery, J. Gagliano, J.E. Hoyt, P.S. Kallakuri
ANL, Lemont, Illinois, USA

Ion instability, in which beam motion couples with trapped ions in an accelerator, is a serious concern for high-brightness electron storage rings. For the APS-Upgrade, we plan to mitigate coherent ion instability using a compensated gap scheme. To study incoherent effects (such as emittance growth), an IONEFFECTS element has been incorporated into the particle tracking code ELEGANT. The simulations include multiple ionization, transverse impedance, and charge variation between bunches. Once these effects are included, the simulations show good agreement with measurements at the present APS. We have also installed a gas injection system, which creates a controlled pressure bump of Nitrogen gas in a short section of the APS ring. The resulting ion instability was studied under a wide variety of beam conditions. For cases with no or insufficient train gaps, large emittance growth was observed. IONEFFECTS simulations of the gas injection experiment and APS-U storage ring show the possibility of runaway emittance blowup, where the blown-up beam traps more ions, driving further instability.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA01

About •

paper received ※ 24 June 2021 paper accepted ※ 27 July 2021 issue date ※ 10 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUXA06

Loss of Transverse Landau Damping by Diffusion in High-Energy Hadron Colliders

1286

S.V. Furuseth, X. Buffat
CERN, Geneva, Switzerland
S.V. Furuseth
EPFL, Lausanne, Switzerland

Circular hadron colliders rely on Landau damping to stabilize the beams. Landau damping depends strongly on the bunch distribution, which is often assumed to be Gaussian in the transverse planes. In this paper, we introduce and explain an instability mechanism observed in the LHC, where Landau damping is eventually lost due to a diffusion that modifies the transverse bunch distribution. The mechanism is caused by a wide-spectrum noise that excites the transverse motion of the beam, which consequently produces wakefields that drive a narrow-spectrum diffusion. It is shown that this diffusion efficiently lowers the stability diagram at the frequency of the least stable coherent mode, leading to a loss of Landau damping after a latency. A semi-analytical model agrees with measurements in dedicated latency experiments performed in the LHC. This instability mechanism explains the need for a stability margin in octupole current in the LHC, relative to the amount needed to stabilize a Gaussian beam. We detail the impact of this mechanism and possible mitigations for the LHC and HL-LHC.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUXA06

About •

paper received ※ 19 May 2021 paper accepted ※ 25 June 2021 issue date ※ 10 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPAB254

Limiting Coherent Longitudinal Beam Oscillations in the EIC Electron Storage Ring

2046

B. Podobedov
Brookhaven National Laboratory (BNL), Electron-Ion Collider, Upton, New York, USA
M. Blaskiewicz
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.
We study coherent longitudinal beam oscillations in the EIC electron storage ring (ESR). We show that to avoid unacceptable hadron emittance growth due to finite crossing angle, the amplitude of these oscillations needs to be limited to a fraction of a millimeter. Using an analytical model we estimate the amplitude of these oscillations under the two scenarios: 1) the beam is passively stable and the oscillations are driven by RF phase noise only; 2) a coupled-bunch instability, presently expected in the ESR, is damped by a longitudinal feedback system. We show that, for the 2nd scenario, comfortable specifications for RF phase noise and feedback sensor noise will be sufficient to maintain the oscillation amplitude within the required limits.

Poster TUPAB254 [1.347 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB254

About •

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

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB082

Single Bunch Instability Simulations in the Storage Ring of the ALS-U Project

2783

D. Wang, K.L.F. Bane, S. De Santis, M.P. Ehrlichman, D. Li, T.H. Luo, O. Omolayo, G. Penn, C. Steier, M. Venturini
LBNL, Berkeley, California, USA

As the broad-band impedance modeling and the vacuum chamber design of the new Advanced Light Source storage ring (ALS- U) reach maturity, we report on progress in single-bunch collective effects studies. A pseudo-Green function wake representing the entire ring was earlier obtained by numerical and analytical methods. Macroparticle simulations using the computer code "elegant" and this wake function are used to determine the instability thresholds for longitudinal and transverse motion. We consider various operating conditions, such as without/with higher-harmonic RF cavities, zero/finite linear chromaticity, and without/with a transverse bunch-by-bunch feedback system. Results show enough margin for the broadband impedance budget when the single-bunch instability thresholds are compared with the design bunch charge.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB082

About •

paper received ※ 20 May 2021 paper accepted ※ 01 July 2021 issue date ※ 12 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB150

Monotron Beam Break Up Instability Analysis

2968

V. Volkov, V.M. Petrov
BINP SB RAS, Novosibirsk, Russia

New features of monotron beam break up (BBU) instability such as the typing of high order monopole modes (HOMs)in each cavity by two classes one of them are stable and other ones are unstable, HOM effective quality factor depending on average beam current, and normalized invariable threshold current individually characterizes each HOM are investigated in this article in detail.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB150

About •

paper received ※ 19 May 2021 paper accepted ※ 09 June 2021 issue date ※ 31 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB151

Regenerative Beam Break Up Instability Analysis

2971

V. Volkov, V.M. Petrov
BINP SB RAS, Novosibirsk, Russia

New features of regenerative beam break up (BBU) instability such as the typing of high order dipole modes (HOMs)in each cavity by two classes, one of them are stable and other ones are unstable, HOM effective quality factor depending on average beam current, and normalized invariable threshold current individually characterizes each HOM are investigated in this article in detail.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB151

About •

paper received ※ 19 May 2021 paper accepted ※ 22 June 2021 issue date ※ 01 September 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB226

Investigation of Vlasov Systems with a Certain Class of Linearly-Collective Hamiltonians

3157

Ph. Amstutz, M. Vogt
DESY, Hamburg, Germany

In many cases the Vlasov equation cannot be solved exactly due its inherent non-linearity arising from collective terms in the Hamiltonian. Based on the analysis of the Hamiltonian’s dependence on the phase-space density and the requirement for self-consistency in this contribution a class of Hamiltonians is defined and characterized. For members of this class the corresponding expansion of the Vlasov equation terminates. The new, potentially non-autonomous, Hamiltonian of the resulting Liouville equation depends only on the initial condition of the phase-space density. Prominent members of this class are Poisson-type kick-Hamiltonians, which we show as an example. We expect these investigations to be a potential starting point for the analysis and conception of operator-splitting schemes or splitting-free methods for beam-dynamics simulation codes.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB226

About •

paper received ※ 18 May 2021 paper accepted ※ 01 July 2021 issue date ※ 17 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB227

Mechanism of Longitudinal Single-Bunch Instability in the CERN SPS

3161

I. Karpov
CERN, Meyrin, Switzerland
M. Gadioux
UCD, Dublin, Ireland

Understanding the origin of beam instabilities is essential for reaching the highest performance of proton synchrotrons. In the present work, the Oide-Yokoya eigenvalue method of solving the linearised Vlasov equation was used to shed light on the mechanism of longitudinal single-bunch instability in the CERN SPS. In particular, semi-analytical calculations were done for the full longitudinal impedance model, taking into account the RF nonlinearity. The obtained results agree well with macro-particle simulations and are consistent with available beam measurements. For the first time, the instability has been interpreted as a coupling of radial modes within a single azimuthal mode, due to a strong potential-well distortion of the synchrotron-frequency distribution. To avoid this instability, a higher RF voltage is required at a given emittance. Thus, the instability mechanism is very different from the loss of Landau damping, which, in contrast, is mitigated by a lower RF voltage. This understanding also allowed us to optimise the RF voltage programmes during the acceleration cycle for high-intensity bunches used in the AWAKE experiment at CERN.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB227

About •

paper received ※ 12 May 2021 paper accepted ※ 01 July 2021 issue date ※ 15 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB228

Modelling and Counteracting Microbunching Instability in Spreader Lines of Radiofrequency and Plasma-Based Accelerators for Free-Electron Lasers

3165

G. Perosa
Università degli Studi di Trieste, Trieste, Italy
S. Di Mitri
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

High energy radiofrequency and plasma-driven accelerators target electron beam brightness suitable for x-ray free-electron lasers. Microbunching instability can be enhanced during beam transport through the spreader line from the accelerator to the undulator, degrading the brightness of the accelerated beam and therefore reducing the lasing efficiency. We present a semi-analytical model of the instability, benchmarked with experimental data at the FERMI free-electron laser, in the presence of intrabeam scattering and beam heating. Strategies for minimization of the instability both in conventional and plasma-based accelerators are discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB228

About •

paper received ※ 19 May 2021 paper accepted ※ 08 July 2021 issue date ※ 02 September 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB229

Transverse Density Pileup and Pattern Formation in Dense Ultracold Electron Beamlets under Coulomb Expansion

3169

A.J. Tencate, K. Bhuyan, B. Erdélyi
Northern Illinois University, DeKalb, Illinois, USA

Funding: This work was sponsored by the US Department of Energy Office of Science under Grant DE-SC0020241.
Dynamic Coulomb expansion of dense particle bunches can lead to transverse density shock-like propagation for nonuniform bunch distributions. Furthermore, under favorable circumstances, multiple bunches in close proximity can collide without crossing to form wheel-and-spoke patterns. This process has been observed experimentally for Rubidium ions, but not yet for electrons, where the dynamics occur over far shorter length scales. We simulate the interaction of electron bunches while varying the initial transverse temperature and density profiles to determine the thresholds that characterize this pattern formation. Additionally, we consider the effects of asymmetries and the impact of a low-density halo on the overall process. The simulations are conducted using a novel high-fidelity algorithm for collisional particle dynamics.

Poster WEPAB229 [7.411 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB229

About •

paper received ※ 19 May 2021 paper accepted ※ 02 July 2021 issue date ※ 13 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB233

Excitation of Micro-Bunching in Short Electron Bunches Using RF Amplitude Modulation

3173

T. Boltz, E. Blomley, M. Brosi, E. Bründermann, B. Härer, A. Mochihashi, A.-S. Müller, P. Schreiber, M. Schuh, M. Yan
KIT, Karlsruhe, Germany

In its short-bunch operation mode, the KIT storage ring KARA provides picosecond-long electron bunches, which emit coherent synchrotron radiation (CSR) up to the terahertz frequency range. Due to the high spatial compression under these conditions, the self-interaction of the bunch with its own emitted CSR induces a wake-field, which significantly influences the longitudinal charge distribution. Above a given threshold current, this leads to the formation of dynamically evolving micro-structures within the bunch and is thus called micro-bunching instability. As CSR is emitted at wavelengths corresponding to the spatial dimension of the emitter, these small structures lead to an increased emission of CSR at higher frequencies. The instability is therefore deliberately induced at KARA to provide intense THz radiation to dedicated experiments. To further increase the emitted power in the desired frequency range, we consider the potential of RF amplitude modulations to intentionally excite this form of micro-bunching in short electron bunches. This work is supported by the BMBF project 05K19VKC TiMo (Federal Ministry of Education and Research).

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB233

About •

paper received ※ 19 May 2021 paper accepted ※ 01 July 2021 issue date ※ 17 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB234

Simulating Two Dimensional Coherent Synchrotron Radiation in Python

3177

W. Lou, Y. Cai, C.E. Mayes, G.R. White
SLAC, Menlo Park, California, USA

Coherent Synchrotron Radiation (CSR) in bending magnets poses an important limit for electron beams to reach high brightness in novel accelerators. While the longitudinal wakefield has been well studied in one-dimensional CSR theory and implemented in various simulation codes, transverse wakefields have received less attention. Following the recently developed two-dimensional CSR theory, we developed a Python code simulating the steady-state two-dimensional CSR effects. The computed CSR wakes have been benchmarked with theory and other simulation codes. To speed up computation speed, the code applies vectorization, parallel processing, and Numba in Python.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB234

About •

paper received ※ 20 May 2021 paper accepted ※ 01 July 2021 issue date ※ 20 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB235

TMCI Theory of Flat Chambers Revisited

3181

T.F. Günzel
ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain

By accounting for the transverse impedance’ quadrupolar component according to the work of R.Lindberg *, no TMCI-instability can be observed in case of a pure horizontal resistive wall impedance of flat vacuum chambers. In order to study this effect more closely, TMCI-theory is reviewed and Lindberg’s work is further developed by including the resonator model as impedance type. The theory is applied to the ALBA-impedance model for the calculation of horizontal TMCI-detuning and threshold. Moreover, a couple of example cases are presented including vertical TMCI-detuning and threshold. Results on both planes are compared to simpler descriptions which account for the quadrupolar impedance effect only by tune shift.
* Ryan Lindberg, Fokker-Planck analysis of transverse collective instabilities in electron storage rings, Phy. Rev. Acc. Beams 19, 124402 (2016)

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB235

About •

paper received ※ 19 May 2021 paper accepted ※ 01 July 2021 issue date ※ 19 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB238

Modeling Short Range Wakefield Effects in a High Gradient Linac

3185

F. Bosco, M. Carillo, L. Faillace, L. Giuliano, M. Migliorati, A. Mostacci, L. Palumbo
Sapienza University of Rome, Rome, Italy
M. Behtouei, L. Faillace, A. Giribono, B. Spataro, C. Vaccarezza
INFN/LNF, Frascati, Italy
F. Bosco, M. Migliorati
INFN-Roma1, Rome, Italy
L. Giuliano, A. Mostacci, L. Palumbo
INFN-Roma, Roma, Italy
J.B. Rosenzweig
UCLA, Los Angeles, California, USA

Funding: This work is supported by DARPA GRIT under contract no. 20204571 and partially by INFN National committee V through the ARYA project.
The interaction of charged beams with the surrounding accelerating structures requires a thorough investigation due to potential negative effects on the phase space quality. Indeed, the wakefields acting back on the beam are responsible for emittance dilution and instabilities, such as the beam break-up, which limit the performances of electron-based radiation sources and linear colliders. Here we introduce a new tracking code which is meant to investigate the effects of short-range transverse wakefields in linear accelerators. The tracking is based on quasi-analytical models for the beam dynamics which, in addition to the basic optics specified by the applied fields, include dipole wakefield forces and a simple approach to account for space-charge effects. Such features provide a reliable tool which easily allows to inspect the performances of a linac. To validate the model, a parallel analysis for a reference case is performed with well-known beam dynamics codes, and comparisons are shown. As an illustrative application, we discuss a study on alignment tolerances evaluating the emittance growth induced by misaligned accelerating sections.

Poster WEPAB238 [1.747 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB238

About •

paper received ※ 18 May 2021 paper accepted ※ 07 July 2021 issue date ※ 01 September 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THXA04

Microbunching Instability in the Presence of Intrabeam Scattering for Single-Pass Accelerators

3692

C.-Y. Tsai
HUST, Wuhan, People’s Republic of China
W. Qin
Lund University, Lund, Sweden

Funding: This work is supported by the Fundamental Research Funds for the Central Universities under Project No. 5003131049 and National Natural Science Foundation of China under project No. 11905073.
Intrabeam scattering (IBS) has long been studied in lepton or hadron storage rings as a slow diffusion process, while the effects of IBS on single-pass or recirculating electron accelerators have drawn attention only in the recent two decades due to the emergence of linac-based or ERL-based 4th-generation light sources, which require high-quality electron beams during the beam transport. Recent experimental measurements indicate that in some parameter regimes, IBS can have a significant influence on microbunched beam dynamics. Here we develop a theoretical formulation* of microbunching instability (MBI) in the presence of IBS for single-pass accelerators. We start from the Vlasov-Fokker-Planck (VFP) equation, combining both collective longitudinal space charge and incoherent IBS effects. The linearized VFP equation with the corresponding coefficients is derived. The evolutions of the phase space density and energy modulations are formulated as a set of coupled integral equations. The formulation** is then applied to a simplified single-pass transport line. The results from the semi-analytical calculation are compared and show good agreement with particle tracking simulations.
* C.-Y. Tsai et al., Phys. Rev. Accel. Beams 23, 124401 (2020)
** C.-Y. Tsai and W. Q, Phys. Plasmas (2021), accepted for publication

Slides THXA04 [2.699 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXA04

About •

paper received ※ 13 May 2021 paper accepted ※ 19 July 2021 issue date ※ 13 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THXA05

A Fast Method of 2D Calculation of Coherent Synchrotron Radiation Wakefield in Relativistic Beams

3696

J. Tang, Z. Huang, G. Stupakov
SLAC, Menlo Park, California, USA

Coherent Synchrotron Radiation (CSR) is regarded as one of the most important reasons that limit beam brightness in modern accelerators. CSR wakefield is often computed in a 1D assuming a line charge, which can become invalid when the beam has a large transverse extension and small bunch length. On the other hand, the existing 2D or 3D codes are often computationally inefficient or incomplete. In our previous work * we developed a new model for fast computation of 2D CSR wakefield in relativistic beams with Gaussian distribution. Here we further generalize this model to achieve self-consistent computation compatible with arbitrary beam distribution and nonlinear magnetic lattice with particle tracking. These new features can enable us to perform realistic simulations and study the physics of CSR beyond 1D in electron beams with extreme short bunch length and high peak current.
* J. Tang and G. Stupakov. NAPAC2019, paper WEPLS09 (2019).

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXA05

About •

paper received ※ 19 May 2021 paper accepted ※ 20 July 2021 issue date ※ 21 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPAB076

Effects of Chromaticity and Synchrotron Emission on Coupled-Bunch Transverse Stability

3937

R.R. Lindberg
ANL, Lemont, Illinois, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
We present a theory that can compute the transverse coupled-bunch instability growth rates at any chromaticity and for any longitudinal potential provided only that the long-range wakefield varies slowly over the bunch. The theory is expressed in terms of the usual coupled-bunch eigenvalues at zero chromaticity, and when the longitudinal motion is simple harmonic our solution only requires numerical root-finding that is easy to implement and fast to solve; the more general case requires some additional calculations but is still relatively fast. The theory predicts that the coupled-bunch growth rates can be significantly reduced when the chromatic betatron tune spread is larger than the coupled-bunch growth rate at zero chromaticity. Our theoretical results are compared favorably with tracking simulations for the long-range resistive wall instability, and we also indicate how damping and diffusion from synchrotron emission can further reduce or even stabilize the dynamics.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB076

About •

paper received ※ 20 May 2021 paper accepted ※ 26 July 2021 issue date ※ 26 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)