LHC luminosity upgrade with large Piwinski angle scheme: a recent look Page: 3 of 3
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(2.3x1034cm2sec-1). The LHC injector chain consists of
four accelerators - LINAC (50 MeV), PSB (1.4 GeV), PS
(26 GeV) and SPS (450 GeV). The full potential of the
injectors is being investigated. The PS in combination
with the PSB will generate the bunches needed for
various LHC filling patterns. Currently, 36 bunches (with
<1.7x1011ppb) of 50 ns bunch spacing (or 72 bunches of
25 ns on demand) are routinely transferred from the PS to
the SPS for the LHC collider operation.
LPA requirement of a single bunch intensity of
-3.6x1011ppb with longitudinal emittance LE(46)-0.3
eVs and transverse emittance -3 m is reached [9] in the
PS and accelerated with >90% efficiency in the SPS. A
tomoscope reconstruction of the phase space distribution
of particles [10] in a single bunch of nearly highest
intensity at 26 GeV in the PS is illustrated in Fig. 1. The
results so far are very promising. However, significant
improvement in rf power and beam loading compensation
are needed to achieve the PS performance necessary to
fulfil the LPA requirements for multiple high intensity
bunches.
The SPS offers real challenges for high intensity beam
acceleration from 26 GeV to 450 GeV. One of the major
problems is e-cloud induced beam instability. The issues
related to beam intensity limits in the SPS prior to 2010
are reviewed in [11]. Recent studies [12] in the SPS
showed that the transverse mode coupling instability
threshold is at about 1.6x10"ppb with the nominal lattice
and close to zero chromaticity, but a new optics with
lower transition energy [13] and/or larger chromaticity
(Q'-2) allow acceleration of bunches with significantly
higher intensity (>3 x 1011ppb).
LHC 7TeV e-cloud: 50 ns (36x4 bunch) Photoelectron, idistr=7, 2.5 eVs
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Figure 3: E-cloud simulations for realistic bunch profiles.
E-CLOUD ISSUES
Recent beam studies [14] have shown that the e-cloud
related vacuum activities and beam instability are next in
line to be addressed for the high intensity operation of the
LHC. Detailed e-cloud simulations for all upgrade
scenarios were performed in the past both for standard
Gaussian bunches as well as for ideal flat bunches [5,15].
In view of the new LPA parameter list shown in Table
1, we have re-evaluated the e-cloud generation forbunches shown in Fig. 1 using an improved version of
ECLOUD. Preliminary results show that the difference in
e-cloud build-up for three different bunch profiles at same
bunch intensity is negligible. Figure 3 shows simulation
results for 4 batches of 36 bunch each with 50 nsec bunch
spacing. A more detailed study of the e-cloud effect based
on the recent measurements is in progress.
In conclusion we have presented an updated parameter
list for the LPA scheme of the LHC luminosity upgrade
based on the recent operational experience of the LHC
complex.
The work is supported by Fermi Research Alliance and
US LHC Accelerator Research Program (LARP) and by
EuCARD-AccNet. One of the authors (CMB) would like
to thank CERN for its hospitality and special thanks are
due to O. Bruning, H. Damerau, E. Shaposhnikova, E.
Mahner, and many CERN collaborators.
REFERENCES
[1] F. Ruggiero, F. Zimmermann, "Luminosity
Optimization Near the Beam-Beam Limit by
Increasing Bunch Length Crossing Angle," PRST-
AB 5, 061001 (2002); H. Damerau, Ph. D.
Dessertation Gesellschaft fur Schwerionenforschung
mbH Plankstrase 1, D-64291 Darmstadt, Germany,
(2005).
[2] F. Ruggiero, G. Rumolo, F. Zimmermann, Y.
Papaphilippou, Proc. RPIA2002, Tsukuba, Japan,
CERN-LHC Project- Report-627 and KEK
Proceedings 2002-30 (2002).
[3] K. Takayama et. al., Phys. Rev. Lett. 88, 144801
(2002).
[4] 'LHC Luminosity and Energy Upgrade : A
Feasibility Study',O. Brining et. al., LHC project
report 626, (2002).
[5] F. Zimmerman, EuCARD-CON-2010-041 (2010).
[6] Werner Herr, (this conference and private
communications).
[7] C. M. Bhat et. al., PAC2009, p4670; C. M. Bhat,
Proc. HHH-2008, page 43 and references therein.
[8] E. Shaposhnikova et al, PAC2005, p2300.
[9] H. Damerau and S. Hancock (private
communications, 2010).
[10] Hancock et. al., EPAC1998, (1998) 1520.
[11]E. Shaposhnikova, Procs. Chamonix 2010; Proc.
HHH-2008, page 43 and references therein.
[12] B. Salvant, et. al. "Probing Intensity Limits of LHC-
type Bunches in SPS with Nominal Optics" (this
Proceedings).
[13] H. Bartosik et. al.," Experimental Studies with Low
Transition Energy Optics in the SPS" (this
Proceedings).
[14] G. Rumolo et. al, (this Proceedings).
[15] H. Maury Cuna, "Electron Cloud Effects in the
LHC," Summary report for HELEN Programme, 15
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Bhat, C.M. & Zimmermann, f. LHC luminosity upgrade with large Piwinski angle scheme: a recent look, article, September 1, 2011; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc840411/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.