IPAC2011 - Table of Session: THOBA (Beam Dynamics and Electromagnetic Fields)

Paper

Title

Page

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]

THOBA02

Experimental Demonstration of Suppression of Coherent Synchrotron Radiation Wake-field

V. Yakimenko, A.V. Fedotov, M.G. Fedurin, D. Kayran, V. Litvinenko
BNL, Upton, Long Island, New York, USA
P. Muggli
MPI, Muenchen, Germany

In this paper we report on a first experimental demonstration of coherent synchrotron radiation (CSR) wake-field suppression by a narrow-gap vacuum chamber. Increase in the beam energy spread and emittance due to emission of coherent synchrotron radiation (CSR) is considered to be a limiting factor a high-current high-brightness beams. At the Brookhaven National Laboratory Accelerator Test Facility (ATF) we experimentally demonstrated the suppression of CSR wake-field - both the average energy loss and he energy spread growth – using polished Al plates. Well characterized electron bunches were propagated through a bending magnet with two parallel Al plates with gap controlled between 1 mm to 12 mm. Contrary to some theoretic predictions, our experimental results show that closing the plates significantly reduces both the beam energy loss and CSR-induced beam energy spread. In this paper we present our experimental results and compare then with rigorous analytical theory. These results open a possibility to predict analytically CSR shielding of future high-current high-brightness beams.

Slides THOBA02 [12.706 MB]

THOBA03

Dual AC Dipole Excitation for the Measurement of Magnetic Multipole Strength from Beam Position Monitor Data*

2865

M. Spata, G.A. Krafft
JLAB, Newport News, Virginia, USA

Funding: Notice: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
An experiment was conducted at Jefferson Lab's Continuous Electron Beam Accelerator Facility to develop a technique for characterizing the nonlinear fields of the beam transport system. Two air-core dipole magnets were simultaneously driven at two different frequencies to provide a time-dependent transverse modulation of the electron beam. Fourier decomposition of beam position monitor data was then used to measure the amplitude of these frequencies at different positions along the beamline. For a purely linear transport system one expects to find solely the frequencies that were applied to the dipoles with amplitudes that depend on the phase advance of the lattice. In the presence of nonlinear fields one expects to also find harmonics of the driving frequencies that depend on the order of the nonlinearity. The technique was calibrated using one of the sextupole magnets in a CEBAF beamline and then applied to a dipole to measure the sextupole and octupole strength of the magnet. A comparison is made between the beam-based measurements, results from TOSCA and data from our Magnet Measurement Facility.

Slides THOBA03 [6.193 MB]

Paper	Title	Page
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]

THOBA02	Experimental Demonstration of Suppression of Coherent Synchrotron Radiation Wake-field
	V. Yakimenko, A.V. Fedotov, M.G. Fedurin, D. Kayran, V. Litvinenko BNL, Upton, Long Island, New York, USA P. Muggli MPI, Muenchen, Germany
	In this paper we report on a first experimental demonstration of coherent synchrotron radiation (CSR) wake-field suppression by a narrow-gap vacuum chamber. Increase in the beam energy spread and emittance due to emission of coherent synchrotron radiation (CSR) is considered to be a limiting factor a high-current high-brightness beams. At the Brookhaven National Laboratory Accelerator Test Facility (ATF) we experimentally demonstrated the suppression of CSR wake-field - both the average energy loss and he energy spread growth – using polished Al plates. Well characterized electron bunches were propagated through a bending magnet with two parallel Al plates with gap controlled between 1 mm to 12 mm. Contrary to some theoretic predictions, our experimental results show that closing the plates significantly reduces both the beam energy loss and CSR-induced beam energy spread. In this paper we present our experimental results and compare then with rigorous analytical theory. These results open a possibility to predict analytically CSR shielding of future high-current high-brightness beams.
	Slides THOBA02 [12.706 MB]

THOBA03	Dual AC Dipole Excitation for the Measurement of Magnetic Multipole Strength from Beam Position Monitor Data*	2865
	M. Spata, G.A. Krafft JLAB, Newport News, Virginia, USA
	Funding: Notice: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. An experiment was conducted at Jefferson Lab's Continuous Electron Beam Accelerator Facility to develop a technique for characterizing the nonlinear fields of the beam transport system. Two air-core dipole magnets were simultaneously driven at two different frequencies to provide a time-dependent transverse modulation of the electron beam. Fourier decomposition of beam position monitor data was then used to measure the amplitude of these frequencies at different positions along the beamline. For a purely linear transport system one expects to find solely the frequencies that were applied to the dipoles with amplitudes that depend on the phase advance of the lattice. In the presence of nonlinear fields one expects to also find harmonics of the driving frequencies that depend on the order of the nonlinearity. The technique was calibrated using one of the sextupole magnets in a CEBAF beamline and then applied to a dipole to measure the sextupole and octupole strength of the magnet. A comparison is made between the beam-based measurements, results from TOSCA and data from our Magnet Measurement Facility.
	Slides THOBA03 [6.193 MB]