Baseline Scenario and Options for 3000 fb -1 LHC Performance drivers LHC Performance limitations and challenges Operation experience from 2010 and 2011 HL Goals Upgrade considerations Potential HL-LHC Beam parameters 1 O. Brüning HL-LHC Public meeting 18. November 2011
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Baseline Scenario and Options for 3000 fb-1
LHC Performance driversLHC Performance limitations and challengesOperation experience from 2010 and 2011HL GoalsUpgrade considerationsPotential HL-LHC Beam parameters
1O. BrüningHL-LHC Public meeting 18. November 2011
Luminosity (round beams):
1) maximize bunch intensity (brightness [Nb/en] if @ beam-beam limit)2) minimize beam size (constant beam power)3) maximize number of bunches4) compensate for ‘R’
Performance optimization for the LHC
2
Operation at performance limit choose parameters that allow higher than design performance leveling mechanisms for controlling performance during run
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revb RfNNnL ee
O. BrüningHL-LHC Public meeting 18. November 2011
Performance Limitations & Challenges for the LHC
3
Bunch Intensity:
1) Beam-Beam interaction limit for beam brightness & crossing angle
2) Collective effects (e.g. TMCI) ca. 3.5 1011 ppb
3) e-cloud effect depends on bunch spacing and number of bunches see the
3) Event pile up and bunch luminosity limit detectors upgrade
O. BrüningHL-LHC Public meeting 18. November 2011
(e.g. ATS S. Fartoukh)
4
Number of bunches:
1) Operation with more than 150 bunches requires crossing angle; Operation with for 25ns bunch spacing and 2808 bunches implies ca. 30 long- range beam-beam interactions /IP 2) Electron cloud effect depends on bunch spacing (next transparency)
3) Total beam power and cleaning efficiency (limit on total beam power) fewer bunches more performing for
limited total current dedicated task in HL-LHC project
for now we assume a
limit of ca. 1 A per beam
5) Injector performance depends on bunch spacing (higher brightness for 50ns) maintain both bunch spacing options (25ns & 50ns)
O. BrüningHL-LHC Public meeting 18. November 2011
Performance Limitations & Challenges for the LHC
25-ns bunch spacing 50-ns bunch spacing
H. Maury
e-cloud contribution acceptable for: 25ns and Nb = 2 1011 if dmax ≤ 1.2
50ns and Nb = 4 1011 if dmax ≤ 1.7
F. Zimmermann, Chamonix 2011
5
Electron cloud effect:
O. BrüningHL-LHC Public meeting 18. November 2011
Performance Limitations & Challenges for the LHC
LHC Challenges: R
6
Geometric luminosity reduction factor:
large crossing angle: reduction of long range beam-beam interactions reduction of head-on beam-beam parameter
reduction of the mechanical aperture reduction of instantaneous luminosity
inefficient use of beam current (machine protection!)
opens the door for efficient luminosity leveling
effective cross sectionPiwinski angle
O. BrüningHL-LHC Public meeting 18. November 2011
LHC Challenges: Beam-Beam Interaction
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Tune spread due to head-on beam-beam interaction wo x-ing: