Measurements, ideas, curiosities
description
Transcript of Measurements, ideas, curiosities
F. RuggieroUniv. “La Sapienza”, Rome, 20–24 March
2006CERN
Measurements, ideas, curiosities
fundamental limitations to the ultimate performance of high-luminosity colliders
Complement to the lecture on Electron Cloud and Beam-Beam Effects
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
Electron Cloud build-up and Le Châtelier’s principle
• Henri Louis Le Châtelier (1850-1936) was a French industrial chemist. In 1888 he made a remarkable observation:
Henri Le Châtelier A man of Principle…
• In modern accelerators we want to accumulate more and more intense, positive beams.
• Nature reacts by the fast build-up of negative electron clouds that tend to neutralize the system!
"If a dynamic equilibrium is disturbed by changing some conditions, the position of equilibrium moves to counteract the change."
3
blue: e-cloud effect observedred: planned accelerators
longer fewer more intense bunches
more ‘ultimate’bunches
Scaling of electron cloud effects
experienceat severalstorage ringssuggests thatthe e-cloudthreshold scales as Nb~tsep
possible LHCupgrades considereithersmaller tsep
with constantNb, or theyincrease tsep
in proportionto Nb
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
Electron-cloud build-up in the LHC
• Beam synchrotron radiation is important• provides source of photo-electrons
• Secondary emission yield (SEY) (E) is important • characterized by peak value max
• determines overall e– density
• e– reflectivity (0) is important• determines survival time of e–
• Bunch intensity Nb and beam fill pattern are important
• Main concern: power deposition by electrons on the cold beam screen
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
Secondary Electron Yieldfor normal electron incidence
R. Cimino et al., Phys. Rev. Lett. 93, 014801 (2004)
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
Electron density [m-3] during the passage of an LHC bunch in a field-free region
HEADTAIL simulation, courtesy E. Benedetto
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
Electron density [m-3] during the passage of an LHC bunch in an SPS dipole (top view)
HEADTAIL simulation, courtesy E. Benedetto
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
Electron flux measured in an SPS dipole (strip detector) with LHC beam at 26 GeV
courtesy G. Arduini and M. Jimenez
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
LHC bunch train at injection in the SPS
Evolution of bunch length and bunch population for the first and the last bunch in an LHC bunch train of 72 bunches. SPS measurements with electron cloud in Aug 2004. Courtesy G. Rumolo, G. Arduini, and F. Roncarolo.
rms
bunch
leng
th (
ns)
bunch
inte
nsi
ty (
au)
time (min) time (min)
Qx=26.135
Qy=26.185
ξx=0.15
ξy=0.1
VRF ~ 3 MV
dampers on coupling:
0.008
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
4pb
HO
rN 2)/(
2
sep
HOparLR dn
/ IP no. of IP’s Qbbtotal
SPS 0.005 3 0.015
Tevatron (pbar) 0.01-0.02 2 0.02-0.04
RHIC 0.002 4 ~0.008
LHC (nominal) 0.0034 3 ~0.01
tune shift from head-on collisions (primary IP’s)
tune shift from long-range collisionsnpar parasitic collisions around each IP
conservative value for total tune spread based on SPScollider experience
Beam-Beam tune spread for round beams
increases for closer bunches or reduced crossing angle
limit on limits Nb/(
*
ccsep
)(
s
sd relative beam-beam separation for full crossing angle c
high-lumi in IP1 and IP5 (ATLAS and CMS), halo collisions in IP2 (ALICE) and low-lumi in IP8 (LHC-b)
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
Beam-Beam tune footprints
Comparison of tune footprints, corresponding to betatron amplitudes extending from 0 to 6 , for LHC nominal (red-dotted), ultimate (green-dashed), and “large Piwinski parameter” configuration (blue-solid) with alternating H-V crossing only in IP1 and IP5. (Courtesy H. Grote)
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
• Effects of long-range beam-beam interaction observable at RHIC injection energy (24.3 GeV) with a single proton bunch per ring
• Bunch intensity Nb~1-21011
Long-Range Beam-Beam Experiment in RHIC, 28 April 2005, Wolfram Fischer et al.
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
collision at s=10.65m
Long-Range Beam-Beam Experiment in RHIC, 28 April 2005, Wolfram Fischer et al.
Beam losses increase when the beam-beam separation at a single parasitic collision point is reduced below ~5 .
1 bunch per ring
Blue beam moved vertically
Tunes: B
(0.739,0.727) Y (0.727,0.738)
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
Electron Cloud: recent links & referenceshttp://ab-abp-rlc.web.cern.ch/ab-abp-rlc-ecloud/(web site on Electron Cloud Effects in the LHC)
http://icfa-ecloud04.web.cern.ch/icfa-ecloud04/(ECLOUD’04 workshop, Napa, California, 19–23 April 2004)
http://www-project.slac.stanford.edu/ilc/testfac/ecloud/elec_cloud.html(web site of ILC Damping Ring Task Force 6)
“Can low energy electrons affect high energy physics accelerators?”, R. Cimino, I.R. Collins, M.A. Furmann, M. Pivi, F. Ruggiero, G. Rumolo, and F. Zimmermann, Phys. Rev. Lett. 93, 014801 (2004)
“Simulation study of electron cloud induced instabilities and emittance growth for the CERN Large Hadron Collider proton beam”, E. Benedetto, D. Schulte, F. Zimmermann, and G. Rumolo, Phys. Rev. ST Accel. Beams 8, 124402 (2005)
“Update on electron-cloud power deposition for the Large Hadron Collider arc dipoles”, M. Furmann and V.H. Chaplin, LBNL-59062/CBP Note 723/LARP-doc-157, March 2006, to appear in Phys. Rev. ST Accel. Beams
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
Beam-Beam: recent links & referenceshttp://wwwslap.cern.ch/collective/zwe/lhcbb/(web site of LHC Beam-Beam studies)
http://www.agsrhichome.bnl.gov/AP/BeamBeam/Workshop03/(Beam-Beam Workshop, Montauk, Long Island, 19–23 May 2003)
“Coherent beam-beam modes in the LHC for multiple bunches, different collision schemes and machine symmetries”, W. Herr and T. Pieloni, Proc. CARE HHH-2004 Workshop, CERN, 8–11 November 2004
“Progress of Beam-Beam Compensation Schemes”, F. Zimmermann and U. Dorda, Proc. LHC-LUMI-05 Workshop, Arcidosso, 31 Aug–3 Sept 2005
“Beam-beam effects in the Tevatron”, V. Shiltsev, Y. Alexahin, V. Lebedev, P. Lebrun, R.S. Moore, T. Sen, A. Tollestrup, A. Valishev, and X.L. Zhang, Phys. Rev. ST Accel. Beams 8, 101001 (2005)
“The effects of solenoids and dipole magnets of LHC experiments”, W. Herr, LHC Project Workshop, Chamonix XV, 23-27 January 2006
F. Ruggiero Electron Cloud and Beam-Beam EffectsCERN
CERN Accelerator Complex (not to scale)