IPAC2011 - List of Authors (Li, K.S.B.)

Paper

Title

Page

Impact of Low Transition Energy Optics to the Electron Cloud Instability of LHC Beams in the SPS

616

H. Bartosik, E. Benedetto, K.S.B. Li, Y. Papaphilippou, G. Rumolo
CERN, Geneva, Switzerland

One of the main limitations for high intensity multi-bunch LHC proton beams in the SPS is imposed by electron cloud instabilities. A new optics of the SPS with lower transition energy was implemented and successfully tested in machine studies. The significant increase of the slippage factor that it provides at injection energy results in the expected increase of the single bunch instability thresholds. In this paper, the impact of this new optics on the electron cloud instability threshold is estimated by using numerical simulations, taking into account the change of the optics functions and the faster synchrotron motion due to the reduced transition energy.

MOPS069

Review of Beam Instabilities in the Presence of Electron Clouds in the LHC

760

K.S.B. Li, G. Rumolo
CERN, Geneva, Switzerland

Recent observations at the LHC indicate the build-up of electron clouds when 50 ns spaced beams are injected into the machine at nominal intensity. These electron clouds are a source of coherent beam instabilities and incoherent emittance growth and limit the achievable luminosity. To better understand the influence of electron clouds on the beam dynamics, simulations have been carried out to study both the coherent and the incoherent effects on the beam. The simulations are performed with the HeadTail tracking code; the usage of new post-processing software allows determining not only the beam intensity thresholds in terms of the central electron cloud density but also the footprint of the beam in tune space. In this paper we review instability thresholds and tune footprints for beams with different emittances and interacting with an electron cloud in field-free or dipole regions.

TUPC050

Impedance Effects in the CLIC Damping Rings

1111

E. Koukovini, K.S.B. Li, N. Mounet, G. Rumolo, B. Salvant
CERN, Geneva, Switzerland

Due to the unprecedented brilliance of the beams, the performance of the Compact Linear Collider (CLIC) damping rings is affected by collective effects. Single bunch instability thresholds based on a broad-band resonator model and the associated coherent tune shifts have been evaluated with the HEADTAIL code. Simulations performed for positive and negative values of chromaticity proved that higher order bunch modes can be potentially dangerous for the beam stability. This study also includes the effects of high frequency resistive wall impedance due to different coatings applied on the chambers of the wigglers for e-cloud mitigation and/or ultra-low vacuum pressure. The impact of the resistive-wall wake fields on the transverse impedance budget is finally discussed.

THOBA01

Electron Cloud Observations in LHC

2862

G. Rumolo, G. Arduini, V. Baglin, H. Bartosik, P. Baudrenghien, N. Biancacci, G. Bregliozzi, S.D. Claudet, R. De Maria, J. Esteban Muller, M. Favier, C. Hansen, W. Höfle, J.M. Jimenez, V. Kain, E. Koukovini, G. Lanza, K.S.B. Li, G.H.I. Maury Cuna, E. Métral, G. Papotti, T. Pieloni, F. Roncarolo, B. Salvant, E.N. Shaposhnikova, R.J. Steinhagen, L.J. Tavian, D. Valuch, W. Venturini Delsolaro, F. Zimmermann
CERN, Geneva, Switzerland
C.M. Bhat
Fermilab, Batavia, USA
U. Iriso
CELLS-ALBA Synchrotron, Cerdanyola del Vallès, Spain
N. Mounet, C. Zannini
EPFL, Lausanne, Switzerland

Operation of LHC with bunch trains different spacings has revealed the formation of an electron cloud inside the machine. The main observations of electron cloud build-up are the pressure rise measured at the vacuum gauges in the warm regions, as well as the increase of the beam screen temperature in the cold regions due to an additional heat load. The effects of the electron cloud were also visible as a strong instability and emittance growth affecting the last bunches of longer trains, which could be improved running with higher chromaticity and/or larger transverse emittances. A summary of the 2010 and 2011 observations and measurements and a comparison with existing models will be presented. The efficiency of scrubbing and scrubbing strategies to improve the machine running performance will be also briefly discussed.

Slides THOBA01 [2.911 MB]

Paper	Title	Page
MOPS011	Impact of Low Transition Energy Optics to the Electron Cloud Instability of LHC Beams in the SPS	616
	H. Bartosik, E. Benedetto, K.S.B. Li, Y. Papaphilippou, G. Rumolo CERN, Geneva, Switzerland
	One of the main limitations for high intensity multi-bunch LHC proton beams in the SPS is imposed by electron cloud instabilities. A new optics of the SPS with lower transition energy was implemented and successfully tested in machine studies. The significant increase of the slippage factor that it provides at injection energy results in the expected increase of the single bunch instability thresholds. In this paper, the impact of this new optics on the electron cloud instability threshold is estimated by using numerical simulations, taking into account the change of the optics functions and the faster synchrotron motion due to the reduced transition energy.

MOPS069	Review of Beam Instabilities in the Presence of Electron Clouds in the LHC	760
	K.S.B. Li, G. Rumolo CERN, Geneva, Switzerland
	Recent observations at the LHC indicate the build-up of electron clouds when 50 ns spaced beams are injected into the machine at nominal intensity. These electron clouds are a source of coherent beam instabilities and incoherent emittance growth and limit the achievable luminosity. To better understand the influence of electron clouds on the beam dynamics, simulations have been carried out to study both the coherent and the incoherent effects on the beam. The simulations are performed with the HeadTail tracking code; the usage of new post-processing software allows determining not only the beam intensity thresholds in terms of the central electron cloud density but also the footprint of the beam in tune space. In this paper we review instability thresholds and tune footprints for beams with different emittances and interacting with an electron cloud in field-free or dipole regions.

TUPC050	Impedance Effects in the CLIC Damping Rings	1111
	E. Koukovini, K.S.B. Li, N. Mounet, G. Rumolo, B. Salvant CERN, Geneva, Switzerland
	Due to the unprecedented brilliance of the beams, the performance of the Compact Linear Collider (CLIC) damping rings is affected by collective effects. Single bunch instability thresholds based on a broad-band resonator model and the associated coherent tune shifts have been evaluated with the HEADTAIL code. Simulations performed for positive and negative values of chromaticity proved that higher order bunch modes can be potentially dangerous for the beam stability. This study also includes the effects of high frequency resistive wall impedance due to different coatings applied on the chambers of the wigglers for e-cloud mitigation and/or ultra-low vacuum pressure. The impact of the resistive-wall wake fields on the transverse impedance budget is finally discussed.

THOBA01	Electron Cloud Observations in LHC	2862
	G. Rumolo, G. Arduini, V. Baglin, H. Bartosik, P. Baudrenghien, N. Biancacci, G. Bregliozzi, S.D. Claudet, R. De Maria, J. Esteban Muller, M. Favier, C. Hansen, W. Höfle, J.M. Jimenez, V. Kain, E. Koukovini, G. Lanza, K.S.B. Li, G.H.I. Maury Cuna, E. Métral, G. Papotti, T. Pieloni, F. Roncarolo, B. Salvant, E.N. Shaposhnikova, R.J. Steinhagen, L.J. Tavian, D. Valuch, W. Venturini Delsolaro, F. Zimmermann CERN, Geneva, Switzerland C.M. Bhat Fermilab, Batavia, USA U. Iriso CELLS-ALBA Synchrotron, Cerdanyola del Vallès, Spain N. Mounet, C. Zannini EPFL, Lausanne, Switzerland
	Operation of LHC with bunch trains different spacings has revealed the formation of an electron cloud inside the machine. The main observations of electron cloud build-up are the pressure rise measured at the vacuum gauges in the warm regions, as well as the increase of the beam screen temperature in the cold regions due to an additional heat load. The effects of the electron cloud were also visible as a strong instability and emittance growth affecting the last bunches of longer trains, which could be improved running with higher chromaticity and/or larger transverse emittances. A summary of the 2010 and 2011 observations and measurements and a comparison with existing models will be presented. The efficiency of scrubbing and scrubbing strategies to improve the machine running performance will be also briefly discussed.
	Slides THOBA01 [2.911 MB]