ICAP2018 - List of Keywords (HOM)

Paper	Title	Other Keywords	Page
SAPAG04	HOM-Mitigation for Future SPS 33-Cell 200 MHz Accelerating Structures	damping, impedance, cavity, 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
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPAF02	SixTrack Project: Status, Runtime Environment, and New Developments	simulation, scattering, collimation, optics	172
	R. De Maria, J. Andersson, L. Field, M. Giovannozzi, P.D. Hermes, N. Hoimyr, G. Iadarola, S. Kostoglou, E.H. Maclean, E. McIntosh, A. Mereghetti, J. Molson, V.K.B. Olsen, D. Pellegrini, T. Persson, M. Schwinzerl, K.N. Sjobak CERN, Geneva, Switzerland E.H. Maclean University of Malta, Information and Communication Technology, Msida, Malta S. Singh Indian Institute of Technology Madras, Chennai, India K.N. Sjobak University of Oslo, Oslo, Norway I. Zacharov EPFL, Lausanne, Switzerland
	Funding: Research supported by the HL-LHC project and Google Summer of Code 2018. SixTrack is a single-particle tracking code for high-energy circular accelerators routinely used at CERN for the Large Hadron Collider (LHC), its luminosity upgrade (HL-LHC), the Future Circular Collider (FCC), and the Super Proton Synchrotron (SPS) simulations. The code is based on a 6D symplectic tracking engine, which is optimised for long-term tracking simulations and delivers fully reproducible results on several platforms. It also includes multiple scattering engines for beam-matter interaction studies, as well as facilities to run integrated simulations with FLUKA and GEANT4. These features differentiate SixTrack from general-purpose, optics-design software like MAD-X. The code recently underwent a major restructuring to merge advanced features into a single branch, such as multiple ion species, interface with external codes, and high-performance input/output (XRootD, HDF5). This restructuring also removed a large number of build flags, instead enabling/disabling the functionality at run-time. In the process, the code was moved from Fortran 77 to Fortran 2018 standard, also allowing and achieving a better modularization. Physics models (beam-beam effects, RF-multipoles, current carrying wires, solenoid, and electron lenses) and methods (symplecticity check) have also been reviewed and refined to offer more accurate results. The SixDesk runtime environment allows the user to manage the large batches of simulations required for accurate predictions of the dynamic aperture. SixDesk supports CERN LSF and HTCondor batch systems, as well as the BOINC infrastructure in the framework of the LHC@Home volunteering computing project. SixTrackLib is a new library aimed at providing a portable and flexible tracking engine for single- and multi-particle problems using the models and formalism of SixTrack. The tracking routines are implemented in a parametrized C code that is specialised to run vectorized in CPUs and GPUs, by using SIMD intrinsics, OpenCL 1.2, and CUDA tech
	Slides TUPAF02 [0.938 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF02
About •	paper received ※ 18 October 2018 paper accepted ※ 24 October 2018 issue date ※ 26 January 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPAF14	Analytical Calculations for Thomson Backscattering Based Light Sources	electron, laser, radiation, scattering	215
	P.I. Volz, A. Meseck HZB, Berlin, Germany
	There is a rising interest in Thomson-backscattering based light sources, as scattering intense laser radiation on MeV electrons produces high energy photons that would require GeV or even TeV electron beams when using conventional undulators or dipoles. Particularly, medium energy high brightness beams delivered by LINACs or Energy Recovery LINACs, such as BERLinPro being built at Helmholtz-Zentrum Berlin, seem suitable for these sources. In order to study the merit of Thomson-backscattering-based light sources, we are developing an analytical code to simulate the characteristics of the Thomson scattered radiation. The code calculates the distribution of scattered radiation depending on the incident angle and polarization of the laser radiation. Also the impact of the incident laser profile and the full 6D bunch profile, including microbunching, are incorporated. The Status of the code and first results will be presented.
	Slides TUPAF14 [3.289 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF14
About •	paper received ※ 21 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)

TUPAG04	Statistical Analysis of the Eigenmode Spectrum in the SRF Cavities with Mechanical Imperfections	cavity, 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
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPAG07	Efficient Computation of Lossy Higher Order Modes in Complex SRF Cavities Using Reduced Order Models and Nonlinear Eigenvalue Problem Algorithms	cavity, GUI, SRF, 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
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPAG14	Constrained Multi-Objective Shape Optimization of Superconducting RF Cavities to Counteract Dangerous Higher Order Modes	cavity, dipole, 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
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Other Keywords

Page

SAPAG04

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

damping, impedance, cavity, 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

Export •

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

TUPAF02

SixTrack Project: Status, Runtime Environment, and New Developments

simulation, scattering, collimation, optics

172

R. De Maria, J. Andersson, L. Field, M. Giovannozzi, P.D. Hermes, N. Hoimyr, G. Iadarola, S. Kostoglou, E.H. Maclean, E. McIntosh, A. Mereghetti, J. Molson, V.K.B. Olsen, D. Pellegrini, T. Persson, M. Schwinzerl, K.N. Sjobak
CERN, Geneva, Switzerland
E.H. Maclean
University of Malta, Information and Communication Technology, Msida, Malta
S. Singh
Indian Institute of Technology Madras, Chennai, India
K.N. Sjobak
University of Oslo, Oslo, Norway
I. Zacharov
EPFL, Lausanne, Switzerland

Funding: Research supported by the HL-LHC project and Google Summer of Code 2018.
SixTrack is a single-particle tracking code for high-energy circular accelerators routinely used at CERN for the Large Hadron Collider (LHC), its luminosity upgrade (HL-LHC), the Future Circular Collider (FCC), and the Super Proton Synchrotron (SPS) simulations. The code is based on a 6D symplectic tracking engine, which is optimised for long-term tracking simulations and delivers fully reproducible results on several platforms. It also includes multiple scattering engines for beam-matter interaction studies, as well as facilities to run integrated simulations with FLUKA and GEANT4. These features differentiate SixTrack from general-purpose, optics-design software like MAD-X. The code recently underwent a major restructuring to merge advanced features into a single branch, such as multiple ion species, interface with external codes, and high-performance input/output (XRootD, HDF5). This restructuring also removed a large number of build flags, instead enabling/disabling the functionality at run-time. In the process, the code was moved from Fortran 77 to Fortran 2018 standard, also allowing and achieving a better modularization. Physics models (beam-beam effects, RF-multipoles, current carrying wires, solenoid, and electron lenses) and methods (symplecticity check) have also been reviewed and refined to offer more accurate results. The SixDesk runtime environment allows the user to manage the large batches of simulations required for accurate predictions of the dynamic aperture. SixDesk supports CERN LSF and HTCondor batch systems, as well as the BOINC infrastructure in the framework of the LHC@Home volunteering computing project. SixTrackLib is a new library aimed at providing a portable and flexible tracking engine for single- and multi-particle problems using the models and formalism of SixTrack. The tracking routines are implemented in a parametrized C code that is specialised to run vectorized in CPUs and GPUs, by using SIMD intrinsics, OpenCL 1.2, and CUDA tech

Slides TUPAF02 [0.938 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF02

About •

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

Export •

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

TUPAF14

Analytical Calculations for Thomson Backscattering Based Light Sources

electron, laser, radiation, scattering

215

P.I. Volz, A. Meseck
HZB, Berlin, Germany

There is a rising interest in Thomson-backscattering based light sources, as scattering intense laser radiation on MeV electrons produces high energy photons that would require GeV or even TeV electron beams when using conventional undulators or dipoles. Particularly, medium energy high brightness beams delivered by LINACs or Energy Recovery LINACs, such as BERLinPro being built at Helmholtz-Zentrum Berlin, seem suitable for these sources. In order to study the merit of Thomson-backscattering-based light sources, we are developing an analytical code to simulate the characteristics of the Thomson scattered radiation. The code calculates the distribution of scattered radiation depending on the incident angle and polarization of the laser radiation. Also the impact of the incident laser profile and the full 6D bunch profile, including microbunching, are incorporated. The Status of the code and first results will be presented.

Slides TUPAF14 [3.289 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF14

About •

paper received ※ 21 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)

TUPAG04

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

cavity, 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

Export •

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

TUPAG07

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

cavity, GUI, SRF, 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

Export •

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

TUPAG14

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

cavity, dipole, 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

Export •

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