ICAP2018 - List of Keywords (cavity)

Paper	Title	Other Keywords	Page
SAPAF03	Comparison of Model-Based and Heuristic Optimization Algorithms Applied to Photoinjectors Using Libensemble	simulation, space-charge, gun, solenoid	22
	N.R. Neveu IIT, Chicago, Illinois, USA S. T. P. Hudson, J.M. Larson ANL, Argonne, Illinois, USA L.K. Spentzouris Illinois Institute of Technology, Chicago, Illinois, USA
	Funding: U.S. DOE, OS, contract DE-AC02-06CH11357 and grant DE-SC0015479. Genetic algorithms are common and often used in the accelerator community. They require large amounts of computational resources and empirical adjustment of hyperparameters. Model based methods are significantly more efficient, but often labeled as unreliable for the nonlinear or unsmooth problems that can be found in accelerator physics. We investigate the behavior of both approaches using a photoinjector operated in the space charge dominated regime. All optimization runs are coordinated and managed by the Python library libEnsemble, which is developed at Argonne National Laboratory.
	Slides SAPAF03 [0.653 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAF03
About •	paper received ※ 11 November 2018 paper accepted ※ 19 November 2018 issue date ※ 26 January 2019
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SAPAF04	Single Objective Genetic Optimization of an 85% Efficient Klystron	klystron, electron, simulation, bunching	25
	A. Jensen, J.J. Petillo Leidos Corp, Billerica, MA, USA R.L. Ives, M.E. Read CCR, San Mateo, California, USA J. Neilson SLAC, Menlo Park, California, USA
	Overall efficiency is a critical priority for the next generation of particle accelerators as they push to higher and higher energies. In a large machine, even a small increase in efficiency of any subsystem or component can lead to a significant operational cost savings. The Core Oscillation Method (COM) and Bunch-Align-Compress (BAC) method have recently emerged as a means to greatly increase the efficiency of the klystron RF source for particle accelerators. The COM and BAC methods both work by uniquely tuning klystron cavity frequencies such that more particles from the anti-bunch are swept into the bunch before power is extracted from the beam. The single objective genetic algorithm from Sandia National Laboratory’s Dakota optimization library is used to optimize both COM and BAC based klystron designs to achieve 85% efficiency. The COM and BAC methods are discussed. Use of the Dakota optimization algorithm library from Sandia National Laboratory is discussed. Scalability of the optimization approach to High Performance Computing (HPC) is discussed. The optimization approach and optimization results are presented.
	Slides SAPAF04 [1.476 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAF04
About •	paper received ※ 16 October 2018 paper accepted ※ 19 November 2018 issue date ※ 26 January 2019
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SAPAG03	Mode-Analysis Methods for the Study of Collective Instabilities in Electron-Storage Rings	damping, impedance, simulation, radiation	30
	M. Venturini LBNL, Berkeley, California, USA
	We report on recent progress on the application of mode analysis to the study of collective instabilities in electron storage rings including Higher Harmonic RF Cavities (HHCs). The focus is on transverse instabilities in the presence of a dominant resistive-wall impedance, a problem of particular relevance to the new generation of diffraction-limited light sources. The secular equation for the system eigenvalues is solved after applying a regularizing transformation, a key step to obtaining numerically accurate solutions. We provide a demonstration that for vanishing chromaticity and in the absence of radiation damping the beam motion is always unstable. This is in contrast to the more conventional Transverse-Mode-Coupling Instability (TMCI) without HHCs, which is known to exhibit a well defined instability threshold.
	Slides SAPAG03 [2.261 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAG03
About •	paper received ※ 18 October 2018 paper accepted ※ 24 October 2018 issue date ※ 26 January 2019
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SAPAG04	HOM-Mitigation for Future SPS 33-Cell 200 MHz Accelerating Structures	HOM, damping, impedance, coupling	35
	P. Kramer, C. Vollinger CERN, Geneva, Switzerland
	The CERN SPS 200 MHz travelling wave (TW) accelerating structures pose an intensity limitation for the planned High Luminosity (HL-) LHC upgrade. Higher-order modes (HOMs) around 630 MHz have been identified as one of the main sources of longitudinal multi-bunch instabilities. Improved mitigation of these HOMs with respect to today’s HOM-damping scheme is therefore an essential part of the LHC injectors upgrade (LIU) project. The basic principles of HOM-couplers in cavities and today’s damping scheme are reviewed, before illustrating the numerous requirements an improved damping scheme for the future 33-cell structures must fulfil. These are, amongst others, the mitigation of HOMs situated in the lower part of the structure where there are no access ports for extraction, a sufficient overall damping performance and an acceptable influence on the fundamental accelerating passband (FPB). Different approaches tackling these challenges are investigated and their performance, advantages and pitfalls are evaluated by ACE3P and CST electromagnetic (EM) field solver suites.
	Slides SAPAG04 [2.184 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAG04
About •	paper received ※ 19 October 2018 paper accepted ※ 24 October 2018 issue date ※ 26 January 2019
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SUPAF08	Particle-in-Cell Simulation of a Bunched Electrons Beam Acceleration in a TE113 Cylindrical Cavity Affected by a Static Inhomogeneous Magnetic Field	electron, acceleration, resonance, simulation	64
	E.A. Orozco UIS, Bucaramanga, Colombia J.R. Beltrán, J.D. González, V.E. Vergara UMAG, Santa Marta, Colombia
	Funding: Universidad Industrial de Santander vice-rectory of research and extension. Mobility program N° Application: 2349 The results of the relativistic full electromagnetic Particle-in-cell (PIC) simulation of a bunched electrons beam accelerated in a TE₁₁₃ cylindrical cavity in the presence of a static inhomogeneous magnetic field are presented. This type of acceleration is known as Spatial AutoResonance Acceleration (SARA). The magnetic field profile is such that it keeps the electrons beam in the acceleration regime along their trajectories. Numerical experiments of bunched electrons beam with the concentrations in the range 10⁸ -10⁹ cm^-3 in a linear TE₁₁₃ cylindrical microwave field of a frequency of 2.45GHz and an amplitude of 15kV /cm show that it is possible accelerate the bunched electrons up to energies of 250keV without serious defocalization effect. A comparison between the data obtained from the full electromagnetic PIC simulations and the results derived from the relativistic Newton-Lorentz equation in a single particle approximation is carried out. This acceleration scheme can be used to produce hard x-ray. Dugar-Zhabon, V. D., & Orozco, E. A. (2009).Physical Review Special Topics-Accelerators and Beams, 12(4), 041301. ** Dugar-Zhabon, V. D., & Orozco, E. A. (2017). (USA Patent: 9,666, 403 )
	Slides SUPAF08 [1.358 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SUPAF08
About •	paper received ※ 21 October 2018 paper accepted ※ 27 January 2019 issue date ※ 26 January 2019
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SUPAG06	Simulation Challenges for eRHIC Beam-Beam Study	electron, simulation, proton, damping	99
	Y. Luo BNL, Upton, Long Island, New York, USA Y. Hao FRIB, East Lansing, USA J. Qiang LBNL, Berkeley, California, USA Y. Roblin JLab, Newport News, Virginia, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The 2015 Nuclear Science Advisory Committee Long Rang Plan identified the need for an electron-ion collider facility as a gluon microscope with capabilities beyond those of any existing accelerator complex. To reach the required high energy, high luminosity, and high polarization, the eRHIC design based on the existing heady ion and polarized proton collider RHIC adopts a very small beta-function at the interaction point, a high collision repetition rate, and a novel hadron cooling scheme. Collision with a full crossing angle of 22 mrad and crab cavities for both electron and proton rings are required. In this article, we will present the high priority R&D items related to beam-beam interaction for the current eRHIC design, the simulation challenges, and our plans to address them.
	Slides SUPAG06 [2.395 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SUPAG06
About •	paper received ※ 18 October 2018 paper accepted ※ 03 December 2018 issue date ※ 26 January 2019
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TUPAF09	Multi Pass Energy Recovery Linac Design With a Single Fixed Field Magnet Return Line	linac, electron, lattice, betatron	191
	D. Trbojevic, J.S. Berg, S.J. Brooks, F. Méot, N. Tsoupas BNL, Upton, Long Island, New York, USA W. Lou Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	We present a new approach of the Energy Recovery Linac Design for the future projects: PERLE (Powerful Energy Recovery Linac for Experiments), LHeC/FCCeH and eR- HIC. The concept uses superconducting linacs and a single xed eld beam line with multiple energy passes of electron beams. This represents an update to the existing CBETA (Cornell University Brookhaven National Laboratory ERL Test Accelerator) where the superconducting linac uses a single xed eld magnet beam line with four energy passes during acceleration and four passes during the energy recov- ery. To match the single xed eld beam line to the linac the CBETA uses the spreaders and combiners on both sides of the linac, while the new concept eliminates them. The arc cells from the single xed eld beam line are connected to the linac with adiabatic transition arcs wher cells increase in length. The orbits of di erent energies merge into a sin- gle orbit through the interleaved linac within the straight sections as in the CBETA project. The betatron functions from the arcs are matched to the linac. The time of ight of di erent electron energies is corrected for the central orbits by additional correction magnet controlled induced beam oscillations.
	Slides TUPAF09 [3.935 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF09
About •	paper received ※ 22 October 2018 paper accepted ※ 27 January 2019 issue date ※ 26 January 2019
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TUPAF12	Longitudinal Beam Dynamics With a Higher-Harmonic Cavity for Bunch Lengthening	operation, storage-ring, simulation, synchrotron	202
	G. Bassi, J. Tagger BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy We discuss the longitudinal beam dynamics in storage rings in the presence of a higher-harmonic cavity (HHC) system for bunch lengthening. We first review the general conditions for HHC operations, either in active or passive mode, assuming the stability of the system. For uniform filling patterns, a distinction is made between operations with a normal-conducting HHC, where optimal conditions for bunch lengthening can be satisfied, and operations with super-conducting HHC, where optimal conditions can be met only approximately. The option to operate the NSLS-II storage ring with a passive, super-conducting third harmonic cavity (3HC) system is discussed next. The stability and performance of the system in the presence of a gap in the uniform filling, which corresponds to the present mode of operation of the NSLS-II storage ring, is investigated with self-consistent Vlasov-Fokker-Planck simulations performed with the code SPACE. G. Bassi, A. Blednykh and V. Smaluk, Phys Rev. Accel. Beams 19, 024401 (2016).
	Slides TUPAF12 [17.562 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF12
About •	paper received ※ 20 October 2018 paper accepted ※ 28 January 2019 issue date ※ 26 January 2019
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TUPAF19	pyaopt Optimization Suite and its Applications to an SRF Cavity Design for UEMs	SRF, gun, simulation, electron	229
	A. Liu, P.V. Avrakhov, R.A. Kostin Euclid TechLabs, LLC, Solon, Ohio, USA C.-J. Jing Euclid Beamlabs LLC, Bolingbrook, USA
	Funding: DOE SBIR In order to achieve sharp, high resolution real-time imaging, electrons in a MeV UEM (ultrafast electron microscope) beamline need to minimize instabilities. The Superconducting RF (SRF) photocathode gun is a promising candidate to produce highly stable electrons for UEM/UED applications. It operates in an ultrahigh Q, CW mode, and dissipates a few watts of RF power, which make it possible to achieve a 10s ppm level of beam stability by using modern RF control techniques. In order to find the best performance of the gun design, an optimization procedure is required. pyaopt is a Python-based optimization suite that supports multi-objective optimizations using advanced algorithms. In this paper, the novel SRF photogun design and its optimizations through pyaopt and Astra’s beam simulations will be discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF19
About •	paper received ※ 22 October 2018 paper accepted ※ 15 December 2018 issue date ※ 26 January 2019
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TUPAG01	Computation of Eigenmodes in the BESSY VSR Cavity Chain by Means of Concatenation Strategies	coupling, impedance, GUI, factory	253
	T. Flisgen, A.V. Vélez HZB, Berlin, Germany J. Heller, G. Zadeh, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Funding: The research leading to these results was supported by the German Bundesministerium für Bildungund Forschung, Land Berlin and grants of Helmholtz Association Invited Talk: The computation of eigenmodes in chains of superconducting cavities with asymmetric couplers is a demanding problem. This problem typically requires the use of high-performance computers in combination with dedicated software packages. Alternatively, the eigenmodes of chains of superconducting cavities can be determined by the so-called State-Space Concatenation (SSC) approach that has been developed at the University of Rostock. SSC is based on the decomposition of the full chain into individual segments. Subsequently, the RF properties of every segment are described by reduced-order models. These reduced-order models are concatenated to a reduced-order model of the entire chain by means of algebraic side constraints arising from continuity conditions of the fields across the decomposition planes. The constructed reduced-order model describes the RF properties of the complete structure so that the field distributions, the coupling impedances and the external quality factors of the eigenmodes of the full cavity chain are available. In contrast to direct methods, SSC allows for the computation of the eigenmodes of cavity chains using desktop computers. The current contribution revises the scheme using the BESSY VSR cavity chain as an example. In addition, a comparison between a direct computation of a specific localized mode is described.
	Slides TUPAG01 [3.483 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG01
About •	paper received ※ 21 October 2018 paper accepted ※ 28 January 2019 issue date ※ 26 January 2019
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TUPAG04	Statistical Analysis of the Eigenmode Spectrum in the SRF Cavities with Mechanical Imperfections	HOM, SRF, linac, cryomodule	265
	A. Lunin, T.N. Khabiboulline, N. Solyak, A.I. Sukhanov, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Funding: Work is supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy The superconducting radio frequency (SRF) technology is progressing rapidly over last decades toward high accelerating gradients and low surface resistance making feasible the particle accelerators operation with high beam currents and long duty factors. However, the coherent RF losses due to high order modes (HOMs) excitation becomes a limiting factor for these regimes. In spite of the operating mode, which is tuned separately, the parameters of HOMs vary from one cavity to another due to finite mechanical tolerances during cavities fabrication. It is vital to know in advance the spread of HOM parameters in order to predict unexpected cryogenic losses, overheating of beam line components and to keep stable beam dynamics. In this paper we present the method of generating the unique cavity geometry with imperfections while preserving operating mode frequency and field flatness. Based on the eigenmode spectrum calculation of series of randomly generated cavities we can accumulate the data for the evaluation the HOM statistics. Finally, we describe the procedure for the estimation of the probability of the resonant HOM losses in the SRF resonators. The study of these effects leads to specifications of SC cavity and cryomodule and can significantly impact on the efficiency and reliability of the machine operation
	Slides TUPAG04 [1.810 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG04
About •	paper received ※ 15 October 2018 paper accepted ※ 28 January 2019 issue date ※ 26 January 2019
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TUPAG07	Efficient Computation of Lossy Higher Order Modes in Complex SRF Cavities Using Reduced Order Models and Nonlinear Eigenvalue Problem Algorithms	GUI, SRF, HOM, impedance	270
	H.W. Pommerenke, J. Heller, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Superconducting radio frequency (SRF) cavities meet the demanding performance requirements of modern accelerators and high-brilliance light sources. For the operation and design of such resonators, a very precise knowledge of their electromagnetic resonances is required. The non-trivial cavity shape demands a numerical solution of Maxwell’s equations to compute the resonant eigenfrequencies, eigenmodes, and their losses. For large and complex structures this is hardly possible on conventional hardware due to the high number of degrees of freedom required to obtain an accurate solution. In previous work it has been shown that the considered problems can be solved on workstation computers without extensive simplification of the structure itself by a combination of State-Space Concatenation (SSC) and Newton iteration to solve the arising nonlinear eigenvalue problem (NLEVP). First, SSC is applied to the complex, closed and thus lossless RF structure. SSC employs a combination of model order reduction and domain decomposition, greatly reducing the computational effort by effectively limiting the considered frequency domain. Next, a perturbation approach based on SSC is used to describe the resonances of the same geometry subject to external losses. This results in a NLEVP which can be solved efficiently by Newton’s method. In this paper, we expand the NLEVP solution algorithm by a contour integral technique, which increases the completeness of the solution set.
	Slides TUPAG07 [11.204 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG07
About •	paper received ※ 18 October 2018 paper accepted ※ 24 October 2018 issue date ※ 26 January 2019
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TUPAG14	Constrained Multi-Objective Shape Optimization of Superconducting RF Cavities to Counteract Dangerous Higher Order Modes	dipole, HOM, impedance, superconducting-RF	293
	M. Kranjcevic, P. Arbenz ETH, Zurich, Switzerland A. Adelmann PSI, Villigen PSI, Switzerland S. Gorgi Zadeh, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	High current storage rings, such as the Z operating mode of the FCC-ee, require superconducting radio frequency (RF) cavities that are optimized with respect to both the fundamental mode and the dangerous higher order modes. In order to optimize the shape of the RF cavity, a constrained multi-objective optimization problem is solved using a massively parallel implementation of an evolutionary algorithm. Additionally, a frequency-fixing scheme is employed to deal with the constraint on the frequency of the fundamental mode. Finally, the computed Pareto front approximation and an RF cavity shape with desired properties are shown.
	Slides TUPAG14 [3.001 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG14
About •	paper received ※ 19 October 2018 paper accepted ※ 10 December 2018 issue date ※ 26 January 2019
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WEPAF04	Longitudinal Beam Dynamics in FRIB and ReA Linacs	rfq, emittance, simulation, linac	330
	A.S. Plastun, P.N. Ostroumov, A.C.C. Villari, Q. Zhao FRIB, East Lansing, USA
	The Front-End and first three cryomodules of the Facility for Rare Isotope Beam (FRIB) at Michigan State University (MSU) commissioned in July, 2018. The paper describes the online tuning procedures of the longitudinal beam dynamics through the FRIB linac. These procedures include tuning of the accelerating field phases and amplitudes in the cavities. We developed an automated simulation-based tuning procedure for the multi-harmonic buncher. In order to tune the radio-frequency quadrupole (RFQ) we measured and calculated its threshold voltage and scanned its longitudinal acceptance. Tuning of the rebunchers and superconducting accelerating cavities is per-formed by means of the phase scans and Time-Of-Flight (TOF) beam energy measurements with beam position and phase monitors. While FRIB is being commissioned, the re-accelerator (ReA3) for rare isotope beams (RIBs) is being upgraded. We redesigned the ReA3 RFQ to improve its cooling system and provide reliable operation with 16.1 MHz prebunched ion beams with A/Q = 5. In order to provide matching of any ReA3 beam both to the following upgrade cryomodules and physics experiments’ requirements, room temperature rebuncher/debuncher is being designed. The design procedure includes the beam dynamics, electromagnetic, thermal and mechanical simulations and optimizations.
	Slides WEPAF04 [2.406 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-WEPAF04
About •	paper received ※ 19 October 2018 paper accepted ※ 28 January 2019 issue date ※ 26 January 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Other Keywords

Page

SAPAF03

Comparison of Model-Based and Heuristic Optimization Algorithms Applied to Photoinjectors Using Libensemble

simulation, space-charge, gun, solenoid

22

N.R. Neveu
IIT, Chicago, Illinois, USA
S. T. P. Hudson, J.M. Larson
ANL, Argonne, Illinois, USA
L.K. Spentzouris
Illinois Institute of Technology, Chicago, Illinois, USA

Funding: U.S. DOE, OS, contract DE-AC02-06CH11357 and grant DE-SC0015479.
Genetic algorithms are common and often used in the accelerator community. They require large amounts of computational resources and empirical adjustment of hyperparameters. Model based methods are significantly more efficient, but often labeled as unreliable for the nonlinear or unsmooth problems that can be found in accelerator physics. We investigate the behavior of both approaches using a photoinjector operated in the space charge dominated regime. All optimization runs are coordinated and managed by the Python library libEnsemble, which is developed at Argonne National Laboratory.

Slides SAPAF03 [0.653 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAF03

About •

paper received ※ 11 November 2018 paper accepted ※ 19 November 2018 issue date ※ 26 January 2019

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SAPAF04

Single Objective Genetic Optimization of an 85% Efficient Klystron

klystron, electron, simulation, bunching

25

A. Jensen, J.J. Petillo
Leidos Corp, Billerica, MA, USA
R.L. Ives, M.E. Read
CCR, San Mateo, California, USA
J. Neilson
SLAC, Menlo Park, California, USA

Overall efficiency is a critical priority for the next generation of particle accelerators as they push to higher and higher energies. In a large machine, even a small increase in efficiency of any subsystem or component can lead to a significant operational cost savings. The Core Oscillation Method (COM) and Bunch-Align-Compress (BAC) method have recently emerged as a means to greatly increase the efficiency of the klystron RF source for particle accelerators. The COM and BAC methods both work by uniquely tuning klystron cavity frequencies such that more particles from the anti-bunch are swept into the bunch before power is extracted from the beam. The single objective genetic algorithm from Sandia National Laboratory’s Dakota optimization library is used to optimize both COM and BAC based klystron designs to achieve 85% efficiency. The COM and BAC methods are discussed. Use of the Dakota optimization algorithm library from Sandia National Laboratory is discussed. Scalability of the optimization approach to High Performance Computing (HPC) is discussed. The optimization approach and optimization results are presented.

Slides SAPAF04 [1.476 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAF04

About •

paper received ※ 16 October 2018 paper accepted ※ 19 November 2018 issue date ※ 26 January 2019

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SAPAG03

Mode-Analysis Methods for the Study of Collective Instabilities in Electron-Storage Rings

damping, impedance, simulation, radiation

30

M. Venturini
LBNL, Berkeley, California, USA

We report on recent progress on the application of mode analysis to the study of collective instabilities in electron storage rings including Higher Harmonic RF Cavities (HHCs). The focus is on transverse instabilities in the presence of a dominant resistive-wall impedance, a problem of particular relevance to the new generation of diffraction-limited light sources. The secular equation for the system eigenvalues is solved after applying a regularizing transformation, a key step to obtaining numerically accurate solutions. We provide a demonstration that for vanishing chromaticity and in the absence of radiation damping the beam motion is always unstable. This is in contrast to the more conventional Transverse-Mode-Coupling Instability (TMCI) without HHCs, which is known to exhibit a well defined instability threshold.

Slides SAPAG03 [2.261 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAG03

About •

paper received ※ 18 October 2018 paper accepted ※ 24 October 2018 issue date ※ 26 January 2019

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SAPAG04

HOM-Mitigation for Future SPS 33-Cell 200 MHz Accelerating Structures

HOM, damping, impedance, coupling

35

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

The CERN SPS 200 MHz travelling wave (TW) accelerating structures pose an intensity limitation for the planned High Luminosity (HL-) LHC upgrade. Higher-order modes (HOMs) around 630 MHz have been identified as one of the main sources of longitudinal multi-bunch instabilities. Improved mitigation of these HOMs with respect to today’s HOM-damping scheme is therefore an essential part of the LHC injectors upgrade (LIU) project. The basic principles of HOM-couplers in cavities and today’s damping scheme are reviewed, before illustrating the numerous requirements an improved damping scheme for the future 33-cell structures must fulfil. These are, amongst others, the mitigation of HOMs situated in the lower part of the structure where there are no access ports for extraction, a sufficient overall damping performance and an acceptable influence on the fundamental accelerating passband (FPB). Different approaches tackling these challenges are investigated and their performance, advantages and pitfalls are evaluated by ACE3P and CST electromagnetic (EM) field solver suites.

Slides SAPAG04 [2.184 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAG04

About •

paper received ※ 19 October 2018 paper accepted ※ 24 October 2018 issue date ※ 26 January 2019

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SUPAF08

Particle-in-Cell Simulation of a Bunched Electrons Beam Acceleration in a TE113 Cylindrical Cavity Affected by a Static Inhomogeneous Magnetic Field

electron, acceleration, resonance, simulation

64

E.A. Orozco
UIS, Bucaramanga, Colombia
J.R. Beltrán, J.D. González, V.E. Vergara
UMAG, Santa Marta, Colombia

Funding: Universidad Industrial de Santander vice-rectory of research and extension. Mobility program N° Application: 2349
The results of the relativistic full electromagnetic Particle-in-cell (PIC) simulation of a bunched electrons beam accelerated in a TE₁₁₃ cylindrical cavity in the presence of a static inhomogeneous magnetic field are presented. This type of acceleration is known as Spatial AutoResonance Acceleration (SARA)*. The magnetic field profile is such that it keeps the electrons beam in the acceleration regime along their trajectories. Numerical experiments of bunched electrons beam with the concentrations in the range 10⁸ -10⁹ cm^-3 in a linear TE₁₁₃ cylindrical microwave field of a frequency of 2.45GHz and an amplitude of 15kV /cm show that it is possible accelerate the bunched electrons up to energies of 250keV without serious defocalization effect. A comparison between the data obtained from the full electromagnetic PIC simulations and the results derived from the relativistic Newton-Lorentz equation in a single particle approximation is carried out. This acceleration scheme can be used to produce hard x-ray**.
* Dugar-Zhabon, V. D., & Orozco, E. A. (2009).Physical Review Special Topics-Accelerators and Beams, 12(4), 041301.
** Dugar-Zhabon, V. D., & Orozco, E. A. (2017). (USA Patent: 9,666, 403 )

Slides SUPAF08 [1.358 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SUPAF08

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paper received ※ 21 October 2018 paper accepted ※ 27 January 2019 issue date ※ 26 January 2019

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SUPAG06

Simulation Challenges for eRHIC Beam-Beam Study

electron, simulation, proton, damping

99

Y. Luo
BNL, Upton, Long Island, New York, USA
Y. Hao
FRIB, East Lansing, USA
J. Qiang
LBNL, Berkeley, California, USA
Y. Roblin
JLab, Newport News, Virginia, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
The 2015 Nuclear Science Advisory Committee Long Rang Plan identified the need for an electron-ion collider facility as a gluon microscope with capabilities beyond those of any existing accelerator complex. To reach the required high energy, high luminosity, and high polarization, the eRHIC design based on the existing heady ion and polarized proton collider RHIC adopts a very small beta-function at the interaction point, a high collision repetition rate, and a novel hadron cooling scheme. Collision with a full crossing angle of 22 mrad and crab cavities for both electron and proton rings are required. In this article, we will present the high priority R&D items related to beam-beam interaction for the current eRHIC design, the simulation challenges, and our plans to address them.

Slides SUPAG06 [2.395 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SUPAG06

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paper received ※ 18 October 2018 paper accepted ※ 03 December 2018 issue date ※ 26 January 2019

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TUPAF09

Multi Pass Energy Recovery Linac Design With a Single Fixed Field Magnet Return Line

linac, electron, lattice, betatron

191

D. Trbojevic, J.S. Berg, S.J. Brooks, F. Méot, N. Tsoupas
BNL, Upton, Long Island, New York, USA
W. Lou
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

We present a new approach of the Energy Recovery Linac Design for the future projects: PERLE (Powerful Energy Recovery Linac for Experiments), LHeC/FCCeH and eR- HIC. The concept uses superconducting linacs and a single xed eld beam line with multiple energy passes of electron beams. This represents an update to the existing CBETA (Cornell University Brookhaven National Laboratory ERL Test Accelerator) where the superconducting linac uses a single xed eld magnet beam line with four energy passes during acceleration and four passes during the energy recov- ery. To match the single xed eld beam line to the linac the CBETA uses the spreaders and combiners on both sides of the linac, while the new concept eliminates them. The arc cells from the single xed eld beam line are connected to the linac with adiabatic transition arcs wher cells increase in length. The orbits of di erent energies merge into a sin- gle orbit through the interleaved linac within the straight sections as in the CBETA project. The betatron functions from the arcs are matched to the linac. The time of ight of di erent electron energies is corrected for the central orbits by additional correction magnet controlled induced beam oscillations.

Slides TUPAF09 [3.935 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF09

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paper received ※ 22 October 2018 paper accepted ※ 27 January 2019 issue date ※ 26 January 2019

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TUPAF12

Longitudinal Beam Dynamics With a Higher-Harmonic Cavity for Bunch Lengthening

operation, storage-ring, simulation, synchrotron

202

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

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy
We discuss the longitudinal beam dynamics in storage rings in the presence of a higher-harmonic cavity (HHC) system for bunch lengthening. We first review the general conditions for HHC operations, either in active or passive mode, assuming the stability of the system. For uniform filling patterns, a distinction is made between operations with a normal-conducting HHC, where optimal conditions for bunch lengthening can be satisfied, and operations with super-conducting HHC, where optimal conditions can be met only approximately. The option to operate the NSLS-II storage ring with a passive, super-conducting third harmonic cavity (3HC) system is discussed next. The stability and performance of the system in the presence of a gap in the uniform filling, which corresponds to the present mode of operation of the NSLS-II storage ring, is investigated with self-consistent Vlasov-Fokker-Planck simulations performed with the code SPACE*.
* G. Bassi, A. Blednykh and V. Smaluk, Phys Rev. Accel. Beams 19, 024401 (2016).

Slides TUPAF12 [17.562 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF12

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paper received ※ 20 October 2018 paper accepted ※ 28 January 2019 issue date ※ 26 January 2019

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TUPAF19

pyaopt Optimization Suite and its Applications to an SRF Cavity Design for UEMs

SRF, gun, simulation, electron

229

A. Liu, P.V. Avrakhov, R.A. Kostin
Euclid TechLabs, LLC, Solon, Ohio, USA
C.-J. Jing
Euclid Beamlabs LLC, Bolingbrook, USA

Funding: DOE SBIR
In order to achieve sharp, high resolution real-time imaging, electrons in a MeV UEM (ultrafast electron microscope) beamline need to minimize instabilities. The Superconducting RF (SRF) photocathode gun is a promising candidate to produce highly stable electrons for UEM/UED applications. It operates in an ultrahigh Q, CW mode, and dissipates a few watts of RF power, which make it possible to achieve a 10s ppm level of beam stability by using modern RF control techniques. In order to find the best performance of the gun design, an optimization procedure is required. pyaopt is a Python-based optimization suite that supports multi-objective optimizations using advanced algorithms. In this paper, the novel SRF photogun design and its optimizations through pyaopt and Astra’s beam simulations will be discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF19

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paper received ※ 22 October 2018 paper accepted ※ 15 December 2018 issue date ※ 26 January 2019

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TUPAG01

Computation of Eigenmodes in the BESSY VSR Cavity Chain by Means of Concatenation Strategies

coupling, impedance, GUI, factory

253

T. Flisgen, A.V. Vélez
HZB, Berlin, Germany
J. Heller, G. Zadeh, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Funding: The research leading to these results was supported by the German Bundesministerium für Bildungund Forschung, Land Berlin and grants of Helmholtz Association
Invited Talk: The computation of eigenmodes in chains of superconducting cavities with asymmetric couplers is a demanding problem. This problem typically requires the use of high-performance computers in combination with dedicated software packages. Alternatively, the eigenmodes of chains of superconducting cavities can be determined by the so-called State-Space Concatenation (SSC) approach that has been developed at the University of Rostock. SSC is based on the decomposition of the full chain into individual segments. Subsequently, the RF properties of every segment are described by reduced-order models. These reduced-order models are concatenated to a reduced-order model of the entire chain by means of algebraic side constraints arising from continuity conditions of the fields across the decomposition planes. The constructed reduced-order model describes the RF properties of the complete structure so that the field distributions, the coupling impedances and the external quality factors of the eigenmodes of the full cavity chain are available. In contrast to direct methods, SSC allows for the computation of the eigenmodes of cavity chains using desktop computers. The current contribution revises the scheme using the BESSY VSR cavity chain as an example. In addition, a comparison between a direct computation of a specific localized mode is described.

Slides TUPAG01 [3.483 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG01

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paper received ※ 21 October 2018 paper accepted ※ 28 January 2019 issue date ※ 26 January 2019

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TUPAG04

Statistical Analysis of the Eigenmode Spectrum in the SRF Cavities with Mechanical Imperfections

HOM, SRF, linac, cryomodule

265

A. Lunin, T.N. Khabiboulline, N. Solyak, A.I. Sukhanov, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Funding: Work is supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy
The superconducting radio frequency (SRF) technology is progressing rapidly over last decades toward high accelerating gradients and low surface resistance making feasible the particle accelerators operation with high beam currents and long duty factors. However, the coherent RF losses due to high order modes (HOMs) excitation becomes a limiting factor for these regimes. In spite of the operating mode, which is tuned separately, the parameters of HOMs vary from one cavity to another due to finite mechanical tolerances during cavities fabrication. It is vital to know in advance the spread of HOM parameters in order to predict unexpected cryogenic losses, overheating of beam line components and to keep stable beam dynamics. In this paper we present the method of generating the unique cavity geometry with imperfections while preserving operating mode frequency and field flatness. Based on the eigenmode spectrum calculation of series of randomly generated cavities we can accumulate the data for the evaluation the HOM statistics. Finally, we describe the procedure for the estimation of the probability of the resonant HOM losses in the SRF resonators. The study of these effects leads to specifications of SC cavity and cryomodule and can significantly impact on the efficiency and reliability of the machine operation

Slides TUPAG04 [1.810 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG04

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paper received ※ 15 October 2018 paper accepted ※ 28 January 2019 issue date ※ 26 January 2019

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TUPAG07

Efficient Computation of Lossy Higher Order Modes in Complex SRF Cavities Using Reduced Order Models and Nonlinear Eigenvalue Problem Algorithms

GUI, SRF, HOM, impedance

270

H.W. Pommerenke, J. Heller, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Superconducting radio frequency (SRF) cavities meet the demanding performance requirements of modern accelerators and high-brilliance light sources. For the operation and design of such resonators, a very precise knowledge of their electromagnetic resonances is required. The non-trivial cavity shape demands a numerical solution of Maxwell’s equations to compute the resonant eigenfrequencies, eigenmodes, and their losses. For large and complex structures this is hardly possible on conventional hardware due to the high number of degrees of freedom required to obtain an accurate solution. In previous work it has been shown that the considered problems can be solved on workstation computers without extensive simplification of the structure itself by a combination of State-Space Concatenation (SSC) and Newton iteration to solve the arising nonlinear eigenvalue problem (NLEVP). First, SSC is applied to the complex, closed and thus lossless RF structure. SSC employs a combination of model order reduction and domain decomposition, greatly reducing the computational effort by effectively limiting the considered frequency domain. Next, a perturbation approach based on SSC is used to describe the resonances of the same geometry subject to external losses. This results in a NLEVP which can be solved efficiently by Newton’s method. In this paper, we expand the NLEVP solution algorithm by a contour integral technique, which increases the completeness of the solution set.

Slides TUPAG07 [11.204 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG07

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paper received ※ 18 October 2018 paper accepted ※ 24 October 2018 issue date ※ 26 January 2019

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TUPAG14

Constrained Multi-Objective Shape Optimization of Superconducting RF Cavities to Counteract Dangerous Higher Order Modes

dipole, HOM, impedance, superconducting-RF

293

M. Kranjcevic, P. Arbenz
ETH, Zurich, Switzerland
A. Adelmann
PSI, Villigen PSI, Switzerland
S. Gorgi Zadeh, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

High current storage rings, such as the Z operating mode of the FCC-ee, require superconducting radio frequency (RF) cavities that are optimized with respect to both the fundamental mode and the dangerous higher order modes. In order to optimize the shape of the RF cavity, a constrained multi-objective optimization problem is solved using a massively parallel implementation of an evolutionary algorithm. Additionally, a frequency-fixing scheme is employed to deal with the constraint on the frequency of the fundamental mode. Finally, the computed Pareto front approximation and an RF cavity shape with desired properties are shown.

Slides TUPAG14 [3.001 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG14

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paper received ※ 19 October 2018 paper accepted ※ 10 December 2018 issue date ※ 26 January 2019

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WEPAF04

Longitudinal Beam Dynamics in FRIB and ReA Linacs

rfq, emittance, simulation, linac

330

A.S. Plastun, P.N. Ostroumov, A.C.C. Villari, Q. Zhao
FRIB, East Lansing, USA

The Front-End and first three cryomodules of the Facility for Rare Isotope Beam (FRIB) at Michigan State University (MSU) commissioned in July, 2018. The paper describes the online tuning procedures of the longitudinal beam dynamics through the FRIB linac. These procedures include tuning of the accelerating field phases and amplitudes in the cavities. We developed an automated simulation-based tuning procedure for the multi-harmonic buncher. In order to tune the radio-frequency quadrupole (RFQ) we measured and calculated its threshold voltage and scanned its longitudinal acceptance. Tuning of the rebunchers and superconducting accelerating cavities is per-formed by means of the phase scans and Time-Of-Flight (TOF) beam energy measurements with beam position and phase monitors. While FRIB is being commissioned, the re-accelerator (ReA3) for rare isotope beams (RIBs) is being upgraded. We redesigned the ReA3 RFQ to improve its cooling system and provide reliable operation with 16.1 MHz prebunched ion beams with A/Q = 5. In order to provide matching of any ReA3 beam both to the following upgrade cryomodules and physics experiments’ requirements, room temperature rebuncher/debuncher is being designed. The design procedure includes the beam dynamics, electromagnetic, thermal and mechanical simulations and optimizations.

Slides WEPAF04 [2.406 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-WEPAF04

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paper received ※ 19 October 2018 paper accepted ※ 28 January 2019 issue date ※ 26 January 2019

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