HB2012 - List of Keywords (impedance)

Paper	Title	Other Keywords	Page
MOP205	Intense Heavy-Ion Bunches in Dual-harmonic RF Systems	ion, factory, space-charge, synchrotron	51
	M. Mehler, O. Chorniy GSI, Darmstadt, Germany O. Boine-Frankenheim TEMF, TU Darmstadt, Darmstadt, Germany O.K. Kester IAP, Frankfurt am Main, Germany
	For the synchrotron's SIS-18 and SIS-100 (FAIR) a dual-harmonic RF system with the harmonic numbers h1=2, h2=4 and h1=10, h2=20 respectively is planned. Such systems flatten the bunch form and increase the bunching factor Bf therefore reducing the transverse space charge force. For high currents cavity beam loading and potential-well distortion will deform the flattened bunch shape and lead to phase shifts. Optimized settings for the difference between the two RF phases and for the synchronous phase of the main RF harmonic are an option to reduce these effects. In this contribution we will analyse further aspects of the matched bunch distribution, possible instabilities of the obtained distribution will be discussed and results of machine experiments in SIS-18 will be presented.

MOP206	Numerical Calculation of Beam Coupling Impedances for the SIS-100 Synchrotron for FAIR	kicker, coupling, space-charge, synchrotron	54
	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, time domain codes are commercially available to calculate the impedance but they become inapplicable at medium and low frequencies. 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++. 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. In future we plan to confirm our simulations with dedicated wire or coil bench measurements.

MOP214	Test System and Characteristics Studies of Ferrite Cores for the CSNS RCS RF System	cavity, power-supply, controls, LLRF	81
	H. Shi, W.L. Huang, X. Li, W. Long, H. Sun, J.Y. Tang, C.L. Zhang IHEP, Beijing, People's Republic of China
	A two-ring ferrite test system for ferrite-loaded cavities of Rapid Cycling Synchrotron (RCS) of China Spallation Neutron Source (CSNS) has been developed. By this system, the RF characteristics of full-sized ferrite cores of RCS cavities have been studied. On dc bias current, the swept frequency range and thresholds of High Loss Effect (HLE) have been presented. On ac bias current of 25 Hz, although the shunt impedance of the cores satisfies the CSNS cavity, comparing with the dc bias, more power dissipation and more required bias current have been observed because the induced magnetic anisotropy of the ferrite cores disappears. Consequently, it is important to evaluate the dynamic features of the cores with 25 Hz bias current for designing the cavities, the power supplies and the bias current sources.

MOP252	Measurements of the LHC Longitudinal Resistive Impedance with Beam	electron, synchrotron, emittance, synchrotron-radiation	183
	J.F. Esteban Müller, T. Argyropoulos, T. Bohl, T. Mastoridis, N. Mounet, G. Papotti, B. Salvant, E.N. Shaposhnikova, D. Valuch CERN, Geneva, Switzerland
	The resistive part of the longitudinal impedance contributes to the heat deposition on different elements in the LHC ring including the beam screens, where it has to be absorbed by the cryogenic system and can be a practical limitation for the maximum beam intensity. In this paper, we present the first measurements of the LHC longitudinal resistive impedance with beam, done through synchronous phase shift measurements during Machine Development sessions in 2012. Synchronous phase shift is measured for different bunch intensities and lengths using the high-precision LHC Beam Phase Module and then data are post-processed to further increase the accuracy. The dependence of the energy loss per particle on bunch length is then obtained and compared with the expected values found using the LHC impedance model.

WEO1A01	Impedance Studies of 2D Azimuthally Symmetric Devices of Finite Length	coupling, resonance, simulation, cavity	344
	N. Biancacci, E. Métral, B. Salvant CERN, Geneva, Switzerland N. Biancacci Rome University La Sapienza, Roma, Italy M. Migliorati, L. Palumbo URLS, Rome, Italy V.G. Vaccaro Naples University Federico II, Mathematical, Physical and Natural Sciences Faculty, Napoli, Italy
	In circular accelerators, the beam quality can be strongly affected by the self-induced electromagnetic fields excited by the beam in the passage through the elements of the accelerator. The beam coupling impedance quantifies this interaction and allows predicting the stability of the dynamics of high intensity, high brilliance beams. The coupling impedance can be evaluated with finite element methods or using analytical methods, such as Field Matching or Mode Matching. In this paper we present an application of the Mode Matching technique for an azimuthally uniform structure of finite length: a cylindrical cavity loaded with a toroidal slab of lossy dielectric, connected with cylindrical beam pipes. In order to take into account the finite length of the structure, with respect to the infinite length approximation, we decompose the fields in the cavity into a set of orthonormal modes. We obtain a complete set of equations using the magnetic field matching and the non-uniform convergence of the electric field on the cavity boundaries. We present benchmarks done with CST Particle Studio simulations and existing analytical formulas, pointing out the effect of finite length and non-relativistic beta.
	Slides WEO1A01 [6.689 MB]

WEO1A02	LHC Impedance Model: Experience with High Intensity Operation in the LHC	octupole, injection, brightness, damping	349
	B. Salvant, O. Aberle, G. Arduini, R.W. Aßmann, V. Baglin, M.J. Barnes, P. Baudrenghien, A. Bertarelli, C. Bracco, R. Bruce, X. Buffat, F. Carra, F. Caspers, G. Cattenoz, S.D. Claudet, H.A. Day, J. Esteban Müller, M. Garlaschè, L. Gentini, B. Goddard, A. Grudiev, B. Henrist, W. Herr, S. Jakobsen, R.J. Jones, G. Lanza, L. Lari, T. Mastoridis, N. Mounet, E. Métral, A.A. Nosych, J.L. Nougaret, S. Persichelli, T. Pieloni, A.M. Piguiet, S. Redaelli, F. Roncarolo, G. Rumolo, B. Salvachua, M. Sapinski, E.N. Shaposhnikova, L.J. Tavian, M.A. Timmins, J.A. Uythoven, A. Vidal, R. Wasef, D. Wollmann CERN, Geneva, Switzerland A.V. Burov Fermilab, Batavia, USA S.M. White BNL, Upton, Long Island, New York, USA
	The CERN Large Hadron Collider (LHC) is now in luminosity production mode and has been pushing its performance in the past months by increasing the proton beam brightness, the collision energy and the machine availability. As a consequence, collective effects have started to become more and more visible and have effectively slowed down the performance increase of the machine. Among these collective effects, the interaction of brighter LHC bunches with the longitudinal and transverse impedance of the machine has been observed to generate beam induced heating and transverse instabilities since 2010. This contribution reviews the current LHC impedance model obtained from theory, simulations and bench measurements as well as a selection of measured effects with the LHC beam.
	Slides WEO1A02 [7.991 MB]

WEO1A03	Resistive Wall Instability in CSNS/RCS	simulation, extraction, injection, wakefield	354
	L. Huang, Y.D. Liu, S. Wang IHEP, Beijing, People's Republic of China
	Rapid Cycling Synchrotron (RCS) of the China Spallation Neutron Source (CSNS) is a high intensity proton accelerator, with average beam power of 100kW. The collective effects caused by the coupling impedance may be the limit to beam power. The impedance estimation for components on beam line shows that the resistive wall impedance and its instability are more serious than any others. Based on the impedance budget, the instability is theoretically estimated. A simple resistive wall wake field model is used to simulate the bunch oscillation and obtain the growth time. In this simulation model, the continuous resistive wall wake field is concentrated to one position in the ring and the long bunch is sliced into many micro-bunches. By tracking the dynamics of the macro-bunches, the transverse growth time are obtained. The simulation results are also confirmed the restriction to instability by natural chromaticity. # Supported by National Natural Science Foundation of China (11175193) *wangs@ihep.ac.cn
	Slides WEO1A03 [1.358 MB]

WEO1C03	Longitudinal Beam Loss Studies of the CERN PS-to-SPS Transfer	cavity, emittance, simulation, injection	439
	H. Timko, T. Argyropoulos, T. Bohl, H. Damerau, J. Esteban Müller, S. Hancock, E.N. Shaposhnikova CERN, Geneva, Switzerland
	Bunch-to-bucket transfer between the Proton Synchrotron (PS) and the Super Proton Synchrotron (SPS) is required before beams can enter the Large Hadron Collider. The overall beam loss at this transfer is currently around 5-10 %, and is increased for higher intensities or larger longitudinal emittances. Previous attempts to reduce the losses with additional RF voltage from spare cavities in the PS were unsuccessful. In this paper, we modelled the complete PS flat-top bunch splitting and rotation manipulations, PS-to-SPS transfer, SPS flat bottom and acceleration ramp using end-to-end simulations. Starting from the measured bunch distributions, the simulations provide an accurate insight into the problem and allow direct benchmarking with experiments. As a result, it was understood and confirmed by measurements that shorter bunches do not necessarily lead to better transmission. The particle distribution in longitudinal phase space at PS extraction should be optimised instead. A significant loss reduction of up to 50 % is expected from simulations; experimental studies are on-going to verify these theoretical findings.
	Slides WEO1C03 [3.903 MB]

THO1C04	Performances and Future Plans of the LHC RF	cavity, klystron, injection, emittance	565
	P. Baudrenghien, T. Mastoridis CERN, Geneva, Switzerland
	The ramp-up of the LHC operation has been exceptionally fast: from the first acceleration of a single bunch at nominal intensity (1.1· E11 p) to 3.5 TeV/c on May 2010, to the accumulation of 11 fb-1 integrated luminosity two years later (June 2012). On the RF side this was made possible by a few key design choices and several developments, that allow reliable LHC operation with 0.35 A DC beam at 4 TeV/c (1380 bunches at 50 ns spacing, 1.5·10¹¹ p per bunch). This paper reviews the RF design and presents its performance. Plans are also outlined that would allow operation with 25 ns bunch spacing (doubling the beam current) and even increased bunch intensity with the target of above 1A DC current per beam, without big modification to the existing RF power system.
	Slides THO1C04 [9.945 MB]

Paper

Title

Other Keywords

Page

MOP205

Intense Heavy-Ion Bunches in Dual-harmonic RF Systems

ion, factory, space-charge, synchrotron

51

M. Mehler, O. Chorniy
GSI, Darmstadt, Germany
O. Boine-Frankenheim
TEMF, TU Darmstadt, Darmstadt, Germany
O.K. Kester
IAP, Frankfurt am Main, Germany

For the synchrotron's SIS-18 and SIS-100 (FAIR) a dual-harmonic RF system with the harmonic numbers h1=2, h2=4 and h1=10, h2=20 respectively is planned. Such systems flatten the bunch form and increase the bunching factor Bf therefore reducing the transverse space charge force. For high currents cavity beam loading and potential-well distortion will deform the flattened bunch shape and lead to phase shifts. Optimized settings for the difference between the two RF phases and for the synchronous phase of the main RF harmonic are an option to reduce these effects. In this contribution we will analyse further aspects of the matched bunch distribution, possible instabilities of the obtained distribution will be discussed and results of machine experiments in SIS-18 will be presented.

MOP206

Numerical Calculation of Beam Coupling Impedances for the SIS-100 Synchrotron for FAIR

kicker, coupling, space-charge, synchrotron

54

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, time domain codes are commercially available to calculate the impedance but they become inapplicable at medium and low frequencies. 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++. 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. In future we plan to confirm our simulations with dedicated wire or coil bench measurements.

MOP214

Test System and Characteristics Studies of Ferrite Cores for the CSNS RCS RF System

cavity, power-supply, controls, LLRF

81

H. Shi, W.L. Huang, X. Li, W. Long, H. Sun, J.Y. Tang, C.L. Zhang
IHEP, Beijing, People's Republic of China

A two-ring ferrite test system for ferrite-loaded cavities of Rapid Cycling Synchrotron (RCS) of China Spallation Neutron Source (CSNS) has been developed. By this system, the RF characteristics of full-sized ferrite cores of RCS cavities have been studied. On dc bias current, the swept frequency range and thresholds of High Loss Effect (HLE) have been presented. On ac bias current of 25 Hz, although the shunt impedance of the cores satisfies the CSNS cavity, comparing with the dc bias, more power dissipation and more required bias current have been observed because the induced magnetic anisotropy of the ferrite cores disappears. Consequently, it is important to evaluate the dynamic features of the cores with 25 Hz bias current for designing the cavities, the power supplies and the bias current sources.

MOP252

Measurements of the LHC Longitudinal Resistive Impedance with Beam

electron, synchrotron, emittance, synchrotron-radiation

183

J.F. Esteban Müller, T. Argyropoulos, T. Bohl, T. Mastoridis, N. Mounet, G. Papotti, B. Salvant, E.N. Shaposhnikova, D. Valuch
CERN, Geneva, Switzerland

The resistive part of the longitudinal impedance contributes to the heat deposition on different elements in the LHC ring including the beam screens, where it has to be absorbed by the cryogenic system and can be a practical limitation for the maximum beam intensity. In this paper, we present the first measurements of the LHC longitudinal resistive impedance with beam, done through synchronous phase shift measurements during Machine Development sessions in 2012. Synchronous phase shift is measured for different bunch intensities and lengths using the high-precision LHC Beam Phase Module and then data are post-processed to further increase the accuracy. The dependence of the energy loss per particle on bunch length is then obtained and compared with the expected values found using the LHC impedance model.

WEO1A01

Impedance Studies of 2D Azimuthally Symmetric Devices of Finite Length

coupling, resonance, simulation, cavity

344

N. Biancacci, E. Métral, B. Salvant
CERN, Geneva, Switzerland
N. Biancacci
Rome University La Sapienza, Roma, Italy
M. Migliorati, L. Palumbo
URLS, Rome, Italy
V.G. Vaccaro
Naples University Federico II, Mathematical, Physical and Natural Sciences Faculty, Napoli, Italy

In circular accelerators, the beam quality can be strongly affected by the self-induced electromagnetic fields excited by the beam in the passage through the elements of the accelerator. The beam coupling impedance quantifies this interaction and allows predicting the stability of the dynamics of high intensity, high brilliance beams. The coupling impedance can be evaluated with finite element methods or using analytical methods, such as Field Matching or Mode Matching. In this paper we present an application of the Mode Matching technique for an azimuthally uniform structure of finite length: a cylindrical cavity loaded with a toroidal slab of lossy dielectric, connected with cylindrical beam pipes. In order to take into account the finite length of the structure, with respect to the infinite length approximation, we decompose the fields in the cavity into a set of orthonormal modes. We obtain a complete set of equations using the magnetic field matching and the non-uniform convergence of the electric field on the cavity boundaries. We present benchmarks done with CST Particle Studio simulations and existing analytical formulas, pointing out the effect of finite length and non-relativistic beta.

Slides WEO1A01 [6.689 MB]

WEO1A02

LHC Impedance Model: Experience with High Intensity Operation in the LHC

octupole, injection, brightness, damping

349

B. Salvant, O. Aberle, G. Arduini, R.W. Aßmann, V. Baglin, M.J. Barnes, P. Baudrenghien, A. Bertarelli, C. Bracco, R. Bruce, X. Buffat, F. Carra, F. Caspers, G. Cattenoz, S.D. Claudet, H.A. Day, J. Esteban Müller, M. Garlaschè, L. Gentini, B. Goddard, A. Grudiev, B. Henrist, W. Herr, S. Jakobsen, R.J. Jones, G. Lanza, L. Lari, T. Mastoridis, N. Mounet, E. Métral, A.A. Nosych, J.L. Nougaret, S. Persichelli, T. Pieloni, A.M. Piguiet, S. Redaelli, F. Roncarolo, G. Rumolo, B. Salvachua, M. Sapinski, E.N. Shaposhnikova, L.J. Tavian, M.A. Timmins, J.A. Uythoven, A. Vidal, R. Wasef, D. Wollmann
CERN, Geneva, Switzerland
A.V. Burov
Fermilab, Batavia, USA
S.M. White
BNL, Upton, Long Island, New York, USA

The CERN Large Hadron Collider (LHC) is now in luminosity production mode and has been pushing its performance in the past months by increasing the proton beam brightness, the collision energy and the machine availability. As a consequence, collective effects have started to become more and more visible and have effectively slowed down the performance increase of the machine. Among these collective effects, the interaction of brighter LHC bunches with the longitudinal and transverse impedance of the machine has been observed to generate beam induced heating and transverse instabilities since 2010. This contribution reviews the current LHC impedance model obtained from theory, simulations and bench measurements as well as a selection of measured effects with the LHC beam.

Slides WEO1A02 [7.991 MB]

WEO1A03

Resistive Wall Instability in CSNS/RCS

simulation, extraction, injection, wakefield

354

L. Huang, Y.D. Liu, S. Wang
IHEP, Beijing, People's Republic of China

Rapid Cycling Synchrotron (RCS) of the China Spallation Neutron Source (CSNS) is a high intensity proton accelerator, with average beam power of 100kW. The collective effects caused by the coupling impedance may be the limit to beam power. The impedance estimation for components on beam line shows that the resistive wall impedance and its instability are more serious than any others. Based on the impedance budget, the instability is theoretically estimated. A simple resistive wall wake field model is used to simulate the bunch oscillation and obtain the growth time. In this simulation model, the continuous resistive wall wake field is concentrated to one position in the ring and the long bunch is sliced into many micro-bunches. By tracking the dynamics of the macro-bunches, the transverse growth time are obtained. The simulation results are also confirmed the restriction to instability by natural chromaticity.
# Supported by National Natural Science Foundation of China (11175193)
*wangs@ihep.ac.cn

Slides WEO1A03 [1.358 MB]

WEO1C03

Longitudinal Beam Loss Studies of the CERN PS-to-SPS Transfer

cavity, emittance, simulation, injection

439

H. Timko, T. Argyropoulos, T. Bohl, H. Damerau, J. Esteban Müller, S. Hancock, E.N. Shaposhnikova
CERN, Geneva, Switzerland

Bunch-to-bucket transfer between the Proton Synchrotron (PS) and the Super Proton Synchrotron (SPS) is required before beams can enter the Large Hadron Collider. The overall beam loss at this transfer is currently around 5-10 %, and is increased for higher intensities or larger longitudinal emittances. Previous attempts to reduce the losses with additional RF voltage from spare cavities in the PS were unsuccessful. In this paper, we modelled the complete PS flat-top bunch splitting and rotation manipulations, PS-to-SPS transfer, SPS flat bottom and acceleration ramp using end-to-end simulations. Starting from the measured bunch distributions, the simulations provide an accurate insight into the problem and allow direct benchmarking with experiments. As a result, it was understood and confirmed by measurements that shorter bunches do not necessarily lead to better transmission. The particle distribution in longitudinal phase space at PS extraction should be optimised instead. A significant loss reduction of up to 50 % is expected from simulations; experimental studies are on-going to verify these theoretical findings.

Slides WEO1C03 [3.903 MB]

THO1C04

Performances and Future Plans of the LHC RF

cavity, klystron, injection, emittance

565

P. Baudrenghien, T. Mastoridis
CERN, Geneva, Switzerland

The ramp-up of the LHC operation has been exceptionally fast: from the first acceleration of a single bunch at nominal intensity (1.1· E11 p) to 3.5 TeV/c on May 2010, to the accumulation of 11 fb-1 integrated luminosity two years later (June 2012). On the RF side this was made possible by a few key design choices and several developments, that allow reliable LHC operation with 0.35 A DC beam at 4 TeV/c (1380 bunches at 50 ns spacing, 1.5·10¹¹ p per bunch). This paper reviews the RF design and presents its performance. Plans are also outlined that would allow operation with 25 ns bunch spacing (doubling the beam current) and even increased bunch intensity with the target of above 1A DC current per beam, without big modification to the existing RF power system.

Slides THO1C04 [9.945 MB]