ICAP2018 - List of Keywords (damping)

Paper	Title	Other Keywords	Page
SAPAG03	Mode-Analysis Methods for the Study of Collective Instabilities in Electron-Storage Rings	cavity, 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, 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)

SUPAF09	Sparse Grid Particle-in-Cell Scheme for Noise Reduction in Beam Simulations	simulation, electron, plasma, target	71
	A.J. Cerfon Courant Institute of Mathematical Sciences, New York University, New York, USA L.F. Ricketson LLNL, Livermore, California, USA
	The complexity of standard solvers grows exponentially with the number of dimensions of the underlying equations. This issue is particularly acute for continuum solvers, which need to discretize the six-dimensional phase-space distribution function, and whose run times are consequently large even for a moderate number of grid points for each dimension. Particle-in-Cell (PIC) schemes are a popular alternate approach to continuum methods, because they only discretize the three-dimensional physical space and are therefore less subject to the curse of dimensionality. Even if so, PIC solvers still have large run times, because of the statistical error which is inherent to particle methods and which decays slowly with the number of particles per cell. In this talk, we will present a new scheme to address the curse of dimensionality and at the same time reduce the numerical noise of PIC simulations. Our PIC scheme is inspired by the sparse grids combination technique, a method invented to reduce grid based error when solving high dimensional partial differential equations [1]. The technique, when applied to the PIC method, has two benefits: 1) it almost eliminates the dependence of the grid based error on dimensionality, just like in a standard sparse grids application; 2) it lowers the statistical error significantly, because the sparse grids have larger cells, and thus a larger number of particles per cell for a given total number of particles. We will analyze the performance of our scheme for standard test problems in beam physics. We will demonstrate remarkable speed up for a certain class of problems, and less impressive performance for others. The latter will allow us to identify the limitations of our scheme and explore ideas to address them. [1] Griebel M et al. 1990 A combination technique for the solution of sparse grid problems Iterative Methods in Linear Algebra ed R Bequwens and P de Groen (Amsterdam: Elsevier) pp 263-81
	Slides SUPAF09 [1.848 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SUPAF09
About •	paper received ※ 19 October 2018 paper accepted ※ 19 November 2018 issue date ※ 26 January 2019
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SUPAG06	Simulation Challenges for eRHIC Beam-Beam Study	electron, simulation, proton, cavity	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
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Other Keywords

Page

SAPAG03

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

cavity, 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

Export •

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

SAPAG04

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

HOM, 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)

SUPAF09

Sparse Grid Particle-in-Cell Scheme for Noise Reduction in Beam Simulations

simulation, electron, plasma, target

71

A.J. Cerfon
Courant Institute of Mathematical Sciences, New York University, New York, USA
L.F. Ricketson
LLNL, Livermore, California, USA

The complexity of standard solvers grows exponentially with the number of dimensions of the underlying equations. This issue is particularly acute for continuum solvers, which need to discretize the six-dimensional phase-space distribution function, and whose run times are consequently large even for a moderate number of grid points for each dimension. Particle-in-Cell (PIC) schemes are a popular alternate approach to continuum methods, because they only discretize the three-dimensional physical space and are therefore less subject to the curse of dimensionality. Even if so, PIC solvers still have large run times, because of the statistical error which is inherent to particle methods and which decays slowly with the number of particles per cell. In this talk, we will present a new scheme to address the curse of dimensionality and at the same time reduce the numerical noise of PIC simulations. Our PIC scheme is inspired by the sparse grids combination technique, a method invented to reduce grid based error when solving high dimensional partial differential equations [1]. The technique, when applied to the PIC method, has two benefits: 1) it almost eliminates the dependence of the grid based error on dimensionality, just like in a standard sparse grids application; 2) it lowers the statistical error significantly, because the sparse grids have larger cells, and thus a larger number of particles per cell for a given total number of particles. We will analyze the performance of our scheme for standard test problems in beam physics. We will demonstrate remarkable speed up for a certain class of problems, and less impressive performance for others. The latter will allow us to identify the limitations of our scheme and explore ideas to address them.
[1] Griebel M et al. 1990 A combination technique for the solution of sparse grid problems Iterative Methods in Linear Algebra ed R Bequwens and P de Groen (Amsterdam: Elsevier) pp 263-81

Slides SUPAF09 [1.848 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SUPAF09

About •

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

Export •

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

SUPAG06

Simulation Challenges for eRHIC Beam-Beam Study

electron, simulation, proton, cavity

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

Export •

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