ICAP2012 - List of Keywords (impedance)

Paper	Title	Other Keywords	Page
MOADI1	High Precision Cavity Simulations	cavity, simulation, resonance, coupling	43
	W. Ackermann, T. Weiland TEMF, TU Darmstadt, Darmstadt, Germany
	Funding: Work supported by DESY, Hamburg The design and optimization of particle accelerator components are fundamentally based on beam dynamics simulations. The knowledge of the interaction of moving charged particles with the surrounding materials and fields enables to optimize individual devices and consequently to take the best advantage of the entire machine. Among the essential accelerator components are radio-frequency cavities which are utilized for acceleration as well as for beam diagnostics. In these applications, precise beam dynamics simulations urgently require high-precision data of the electromagnetic fields. Numerical simulations based on Maxwell’s equations have to represent the resulting fields on an acceptable level of quality even with limited amount of degrees of freedom. On the other hand, the particle beam itself gives rise to the excitation of undesired modes which have to be extracted from the cavities. In the current work, some of the challenges faced in high precision cavity simulations are summarized. Based on high-performance eigenvalue calculations, important features like "low-noise" field evaluations or port-mode boundary approximations to enable traveling-wave transport are addressed.
	Slides MOADI1 [4.234 MB]

WEP12	Realistic 3-Dimensional Eigenmodal Analysis of Electromagnetic Cavities using Surface Impedance Boundary Conditions	cavity, resonance, radio-frequency, simulation	161
	H. Guo, B.S.C. Oswald PSI, Villigen, Switzerland P. Arbenz ETH, Zurich, Switzerland
	Funding: The work of the first author (H. Guo) was supported in part by grant no. 200021-117978 of the Swiss National Science Foundation. The new X-ray Free Electron Laser (SwissFEL) at the Paul Scherrer Institute (PSI) employs, among many other radio frequency elements, a transverse deflecting cavity for beam diagnostics. Since the fabrication process is expensive, an accurate 3-D eigenmodal analysis is indispensable. The software package Femaxx has been developed for solving large scale eigenvalue problems on distributed memory parallel computers. Usually, it is sufficient to assume that the tangential electric field vanishes on the cavity wall. To better approximate reality, we consider the cavity wall conductivity is large but finite, and thus the tangential electrical field on the wall is nonzero. We use the surface impedance boundary conditions (SIBC) arising from the skin-effect model. The resulting nonlinear eigenvalue problem is solved with a nonlinear Jacobi–Davidson method. We demonstrate the performance of the method. First, we investigate the fundamental mode of a pillbox cavity. We study resonance, skin depth and quality factor as a function of the cavity wall conductivity. Second, we analyze the transverse deflecting cavity to assess the capability of the method for technologically relevant problems.

WESCI1	EM Simulations in Beam Coupling Impedance Studies: Some Examples of Application	kicker, simulation, resonance, extraction	190
	C. Zannini, G. Rumolo CERN, Geneva, Switzerland C. Zannini EPFL, Lausanne, Switzerland
	In the frame of the SPS upgrade an accurate impedance model is needed in order to predict the instability threshold and if necessary to start a campaign of impedance reduction. Analytical models, 3-D simulations and bench measurements are used to estimate the impedance contribution of the different devices along the machine. Special attention is devoted to the estimation of the impedance contribution of the kicker magnets that are suspected to be the most important impedance source in SPS. In particular a numerical study is carried out to analyze the effect of the serigraphy in the SPS extraction kicker. An important part of the devices simulations are the ferrite model. For this reason a numerical based method to measure the electromagnetic properties of the material has been developed to measure the ferrite properties. A simulation technique, in order to account for external cable is developed. The simulation results were benchmarked with analytical models and observations with beam. A numerical study was also performed to investigate the limits of the wire method for beam coupling impedance measurements.
	Slides WESCI1 [1.571 MB]

WESCI2	Numerical Calculation of Beam Coupling Impedances in the Frequency Domain using FIT	kicker, space-charge, coupling, simulation	193
	U. Niedermayer, O. Boine-Frankenheim TEMF, TU Darmstadt, Darmstadt, Germany
	The transverse impedance of kicker magnets is considered to be one of the main beam instability sources in the projected SIS-100 at FAIR and also in the SPS at CERN. The longitudinal impedance can contribute to the heat load, which is especially a concern in the cold sections of SIS-100 and LHC. In the high frequency range, commercially available time domain codes like CST Particle Studio® serve to calculate the impedance but they become inapplicable at medium and low frequencies which become more important for larger size synchrotrons. We present the ongoing work of developing a Finite Integration (FIT) solver in frequency domain which is based on the Parallel and Extensible Toolkit for Scientific computing (PETSc) framework in C++. Pre- and post-processing are done in MATLAB®. Infinite beam pipe boundary conditions are used. The code is applied to an inductive insert used to compensate the longitudinal space charge impedance in low energy machines. Another application focuses on the impedance contribution of a ferrite kicker with inductively coupled pulse forming network (PFN) and frequency dependent complex material permeability.
	Slides WESCI2 [3.468 MB]

WESCI3	Electromagnetic Characterization of Materials for the CLIC Damping Rings	simulation, damping, electron, vacuum	198
	E. Koukovini-Platia, G. De Michele, G. Rumolo CERN, Geneva, Switzerland C. Zannini EPFL, Lausanne, Switzerland
	The performance of the Compact Linear Collider (CLIC) damping rings (DR) is likely to be limited by collective effects due to the unprecedented brilliance of the beams. Coating will be used in both electron (EDR) and positron damping rings (PDR) to suppress effects like electron cloud formation or ion instabilities. The impedance modeling of the chambers, necessary for the instabilities studies which will ensure safe operation under nominal conditions, must include the contribution from the coating materials applied for electron cloud mitigation and/or ultra-low vacuum pressure. This advocates for a correct characterization of this impedance in a high frequency range, which is still widely unexplored. The electrical conductivity of the materials in the frequency range of few GHz is determined with the waveguide method, based on a combination of experimental measurements of the complex transmission coefficient S21 and CST 3D electromagnetic (EM) simulations.
	Slides WESCI3 [2.488 MB]

THACI1	Lumped Equivalent Models of Complex RF Structures	HOM, RF-structure, scattering, factory	245
	T. Flisgen, J. Heller, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Funding: partly funded by EU FP7 Research Infrastructure Grant No. 227579 The prediction of RF properties of complex accelerating structures is an important issue in computational accelerator physics. This paper describes the derivation of state space equations for complex structures based on real eigenmodes of sections of the decomposed complex structure. The state space equations enable the calculation of system responses due to port excitations by means of standard ordinary differential equation solvers. Therefore, the state space equations are referred to as lumped equivalent models of such complex RF structures. Besides fast computation of system responses, the equivalent models enable the calculation of secondary quantities such as external quality factors. The present contribution discusses theoretical aspects and illustrates an application example.
	Slides THACI1 [1.538 MB]

THSDI2	Simulation of Multibunch Instabilities with the HEADTAIL Code	simulation, octupole, wakefield, synchrotron	262
	N. Mounet, E. Métral, G. Rumolo CERN, Geneva, Switzerland
	Multibunch instabilities due to beam-coupling impedance can be a critical limitation for synchrotrons operating with many bunches. To study these instabilities, the HEADTAIL code has been extended to simulate the motion of many bunches under the action of wake fields. All the features already present in the single-bunch version of the code have remained available, in particular synchrotron motion, chromaticity, amplitude detuning due to octupoles and the ability to load any kind of wake fields through tables. The code has been then parallelized in order to track thousands of bunches in a reasonable amount of time, showing a linear scaling with the number of processors used. We show benchmarks against Laclare's theory in simple cases, obtaining a good agreement. Results for bunch trains in the LHC and comparison with beam-based measurements are also exhibited.
	Slides THSDI2 [7.278 MB]

Paper

Title

Other Keywords

Page

MOADI1

High Precision Cavity Simulations

cavity, simulation, resonance, coupling

43

W. Ackermann, T. Weiland
TEMF, TU Darmstadt, Darmstadt, Germany

Funding: Work supported by DESY, Hamburg
The design and optimization of particle accelerator components are fundamentally based on beam dynamics simulations. The knowledge of the interaction of moving charged particles with the surrounding materials and fields enables to optimize individual devices and consequently to take the best advantage of the entire machine. Among the essential accelerator components are radio-frequency cavities which are utilized for acceleration as well as for beam diagnostics. In these applications, precise beam dynamics simulations urgently require high-precision data of the electromagnetic fields. Numerical simulations based on Maxwell’s equations have to represent the resulting fields on an acceptable level of quality even with limited amount of degrees of freedom. On the other hand, the particle beam itself gives rise to the excitation of undesired modes which have to be extracted from the cavities. In the current work, some of the challenges faced in high precision cavity simulations are summarized. Based on high-performance eigenvalue calculations, important features like "low-noise" field evaluations or port-mode boundary approximations to enable traveling-wave transport are addressed.

Slides MOADI1 [4.234 MB]

WEP12

Realistic 3-Dimensional Eigenmodal Analysis of Electromagnetic Cavities using Surface Impedance Boundary Conditions

cavity, resonance, radio-frequency, simulation

161

H. Guo, B.S.C. Oswald
PSI, Villigen, Switzerland
P. Arbenz
ETH, Zurich, Switzerland

Funding: The work of the first author (H. Guo) was supported in part by grant no. 200021-117978 of the Swiss National Science Foundation.
The new X-ray Free Electron Laser (SwissFEL) at the Paul Scherrer Institute (PSI) employs, among many other radio frequency elements, a transverse deflecting cavity for beam diagnostics. Since the fabrication process is expensive, an accurate 3-D eigenmodal analysis is indispensable. The software package Femaxx has been developed for solving large scale eigenvalue problems on distributed memory parallel computers. Usually, it is sufficient to assume that the tangential electric field vanishes on the cavity wall. To better approximate reality, we consider the cavity wall conductivity is large but finite, and thus the tangential electrical field on the wall is nonzero. We use the surface impedance boundary conditions (SIBC) arising from the skin-effect model. The resulting nonlinear eigenvalue problem is solved with a nonlinear Jacobi–Davidson method. We demonstrate the performance of the method. First, we investigate the fundamental mode of a pillbox cavity. We study resonance, skin depth and quality factor as a function of the cavity wall conductivity. Second, we analyze the transverse deflecting cavity to assess the capability of the method for technologically relevant problems.

WESCI1

EM Simulations in Beam Coupling Impedance Studies: Some Examples of Application

kicker, simulation, resonance, extraction

190

C. Zannini, G. Rumolo
CERN, Geneva, Switzerland
C. Zannini
EPFL, Lausanne, Switzerland

In the frame of the SPS upgrade an accurate impedance model is needed in order to predict the instability threshold and if necessary to start a campaign of impedance reduction. Analytical models, 3-D simulations and bench measurements are used to estimate the impedance contribution of the different devices along the machine. Special attention is devoted to the estimation of the impedance contribution of the kicker magnets that are suspected to be the most important impedance source in SPS. In particular a numerical study is carried out to analyze the effect of the serigraphy in the SPS extraction kicker. An important part of the devices simulations are the ferrite model. For this reason a numerical based method to measure the electromagnetic properties of the material has been developed to measure the ferrite properties. A simulation technique, in order to account for external cable is developed. The simulation results were benchmarked with analytical models and observations with beam. A numerical study was also performed to investigate the limits of the wire method for beam coupling impedance measurements.

Slides WESCI1 [1.571 MB]

WESCI2

Numerical Calculation of Beam Coupling Impedances in the Frequency Domain using FIT

kicker, space-charge, coupling, simulation

193

U. Niedermayer, O. Boine-Frankenheim
TEMF, TU Darmstadt, Darmstadt, Germany

The transverse impedance of kicker magnets is considered to be one of the main beam instability sources in the projected SIS-100 at FAIR and also in the SPS at CERN. The longitudinal impedance can contribute to the heat load, which is especially a concern in the cold sections of SIS-100 and LHC. In the high frequency range, commercially available time domain codes like CST Particle Studio® serve to calculate the impedance but they become inapplicable at medium and low frequencies which become more important for larger size synchrotrons. We present the ongoing work of developing a Finite Integration (FIT) solver in frequency domain which is based on the Parallel and Extensible Toolkit for Scientific computing (PETSc) framework in C++. Pre- and post-processing are done in MATLAB®. Infinite beam pipe boundary conditions are used. The code is applied to an inductive insert used to compensate the longitudinal space charge impedance in low energy machines. Another application focuses on the impedance contribution of a ferrite kicker with inductively coupled pulse forming network (PFN) and frequency dependent complex material permeability.

Slides WESCI2 [3.468 MB]

WESCI3

Electromagnetic Characterization of Materials for the CLIC Damping Rings

simulation, damping, electron, vacuum

198

E. Koukovini-Platia, G. De Michele, G. Rumolo
CERN, Geneva, Switzerland
C. Zannini
EPFL, Lausanne, Switzerland

The performance of the Compact Linear Collider (CLIC) damping rings (DR) is likely to be limited by collective effects due to the unprecedented brilliance of the beams. Coating will be used in both electron (EDR) and positron damping rings (PDR) to suppress effects like electron cloud formation or ion instabilities. The impedance modeling of the chambers, necessary for the instabilities studies which will ensure safe operation under nominal conditions, must include the contribution from the coating materials applied for electron cloud mitigation and/or ultra-low vacuum pressure. This advocates for a correct characterization of this impedance in a high frequency range, which is still widely unexplored. The electrical conductivity of the materials in the frequency range of few GHz is determined with the waveguide method, based on a combination of experimental measurements of the complex transmission coefficient S21 and CST 3D electromagnetic (EM) simulations.

Slides WESCI3 [2.488 MB]

THACI1

Lumped Equivalent Models of Complex RF Structures

HOM, RF-structure, scattering, factory

245

T. Flisgen, J. Heller, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Funding: partly funded by EU FP7 Research Infrastructure Grant No. 227579
The prediction of RF properties of complex accelerating structures is an important issue in computational accelerator physics. This paper describes the derivation of state space equations for complex structures based on real eigenmodes of sections of the decomposed complex structure. The state space equations enable the calculation of system responses due to port excitations by means of standard ordinary differential equation solvers. Therefore, the state space equations are referred to as lumped equivalent models of such complex RF structures. Besides fast computation of system responses, the equivalent models enable the calculation of secondary quantities such as external quality factors. The present contribution discusses theoretical aspects and illustrates an application example.

Slides THACI1 [1.538 MB]

THSDI2

Simulation of Multibunch Instabilities with the HEADTAIL Code

simulation, octupole, wakefield, synchrotron

262

N. Mounet, E. Métral, G. Rumolo
CERN, Geneva, Switzerland

Multibunch instabilities due to beam-coupling impedance can be a critical limitation for synchrotrons operating with many bunches. To study these instabilities, the HEADTAIL code has been extended to simulate the motion of many bunches under the action of wake fields. All the features already present in the single-bunch version of the code have remained available, in particular synchrotron motion, chromaticity, amplitude detuning due to octupoles and the ability to load any kind of wake fields through tables. The code has been then parallelized in order to track thousands of bunches in a reasonable amount of time, showing a linear scaling with the number of processors used. We show benchmarks against Laclare's theory in simple cases, obtaining a good agreement. Results for bunch trains in the LHC and comparison with beam-based measurements are also exhibited.

Slides THSDI2 [7.278 MB]