Transcript Pergine Slides - Istituto Nazionale di Fisica Nucleare

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
CERN
Univ. “La Sapienza”, Rome, 20–24 March 2006
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:
"If a dynamic equilibrium is
disturbed by changing some
conditions, the position of
equilibrium moves to counteract the
change."
• 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
Henri Le Châtelier
neutralize the system!
A man of Principle…
CERN
F. Ruggiero
Electron Cloud and Beam-Beam Effects
Scaling of electron cloud effects
blue: e-cloud effect observed
red: planned accelerators
more ‘ultimate’
bunches
longer fewer more
intense bunches
experience
at several
storage rings
suggests that
the e-cloud
threshold
scales as
Nb~Dtsep
possible LHC
upgrades
consider
either
smaller Dtsep
with constant
Nb, or they
increase Dtsep
in proportion
to Nb
3
Electron-cloud build-up in the LHC
•
Beam synchrotron radiation is important
• provides source of photo-electrons
•
Secondary emission yield (SEY) d(E) is important
• characterized by peak value dmax
• determines overall e– density
•
e– reflectivity d(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
CERN
Electron Cloud and Beam-Beam Effects
Secondary Electron Yield
for normal electron incidence
R. Cimino et al., Phys. Rev. Lett. 93, 014801 (2004)
F. Ruggiero
CERN
Electron Cloud and Beam-Beam Effects
Electron density [m-3] during the passage of
an LHC bunch in a field-free region
F. Ruggiero
CERN
HEADTAIL simulation, courtesy E. Benedetto
Electron Cloud and Beam-Beam Effects
Electron density [m-3] during the passage of
an LHC bunch in an SPS dipole (top view)
F. Ruggiero
CERN
HEADTAIL simulation, courtesy E. Benedetto
Electron Cloud and Beam-Beam Effects
Electron flux measured in an SPS dipole
(strip detector) with LHC beam at 26 GeV
F. Ruggiero
CERN
courtesy G. Arduini and M. Jimenez
Electron Cloud and Beam-Beam Effects
ξx=0.15
ξy=0.1
bunch intensity (au)
Qx=26.135
Qy=26.185
rms bunch length (ns)
LHC bunch train at injection in the SPS
VRF ~ 3 MV
dampers on
coupling: 0.008
time (min)
time (min)
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.
F. Ruggiero
CERN
Electron Cloud and Beam-Beam Effects
Beam-Beam tune spread for round beams
tune shift from head-on
collisions (primary IP’s)
 HO
N b rp limit on HO

4 limits Nb/()
tune shift from long-range collisions
npar parasitic collisions around each IP
 LR  2n par
increases for closer
 HO
bunches or reduced
( dsep /  ) 2 crossing angle
s
 * relative beam-beam separation
 c
 c

 ( s)
 for full crossing angle c
d sep
HO / IP
no. of IP’s DQbb total
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
high-lumi in IP1 and IP5 (ATLAS
and CMS), halo collisions in IP2
(ALICE) and low-lumi in IP8 (LHC-b)
F. Ruggiero
CERN
conservative value for total
tune spread based on SPS
collider experience
Electron Cloud and Beam-Beam Effects
Beam-Beam tune footprints
Comparison of tune footprints, corresponding to betatron amplitudes
extending from 0 to 6  , for LHC nominal (red-dotted), ultimate (greendashed), and “large Piwinski parameter” configuration (blue-solid) with
alternating H-V crossing only in IP1 and IP5. (Courtesy H. Grote)
F. Ruggiero
CERN
Electron Cloud and Beam-Beam Effects
Long-Range Beam-Beam Experiment in
RHIC, 28 April 2005, Wolfram Fischer et al.
• 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~1-21011
F. Ruggiero
CERN
Electron Cloud and Beam-Beam Effects
Long-Range Beam-Beam Experiment in
RHIC, 28 April 2005, Wolfram Fischer et al.
collision at s=10.65m
1 bunch
per ring
Blue beam
moved
vertically
Tunes:
B (0.739,0.727)
Y (0.727,0.738)
Beam losses increase when the beam-beam separation at a
single parasitic collision point is reduced below ~5 .
CERN
F. Ruggiero
Electron Cloud and Beam-Beam Effects
Electron Cloud: recent links & references
http://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-doc157, March 2006, to appear in Phys. Rev. ST Accel. Beams
F. Ruggiero
CERN
Electron Cloud and Beam-Beam Effects
Beam-Beam: recent links & references
http://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
CERN
Electron Cloud and Beam-Beam Effects
CERN Accelerator Complex (not to scale)
F. Ruggiero
CERN
Electron Cloud and Beam-Beam Effects