Summary notes of the HSS meeting on 26/05/2014

Present: JB, RB, HB, LD, SF, MF, SG, MG, JJ, EM, TP, AS, MS, RT

Report from meetings

• SLM and general information -> MG
  Massimo reminds us about the deadlines for IPAC -  starting today with reports to be sent to him.
  The ABP meeting and BBQ first planned for 5 June would have clashed with the CERN relay race and was postponed to September.
  The MAD-X online model activity is now lead by Piotr Skowronski.
• Collimation Status -> SR
  Collimation production going very well. Essentially completed at CINEL: they reached the 4 coll/month prod rate. All the 16 TCT's required for LS1 installation have been delivered. CERN work to prepare installation ongoing. Now CINEL is producing 4 spares.  
  Agreed with HL management to re-use the CINEL production contract to build 5 TCT's with wire (4 for the MD + 1 spare). A 2.5MCHF MD on the BBLR compensation.
  US-LARP CM meeting + visit to FNAL -> visit attached to the CM to put CERN engineers of MME in contact to the hollow elens hardware experts at FNAL. Very useful visit, discussed also synergy for BB LR compensation.
  EuCARD2 meeting: SR and AR represented the collimation WP11. Good program, in particular on beam tests: novel collimator materials have been irradiated at GSI. Two plenary talks: AR on the general WP status +J. Stadlmann on GSI tests (on behalf of M. Tomut).

First beam-beam considerations on crossing angles: 2012 experience and possible 2015 scenarios  -> TP (slides)

The presentation is given by Tatiana in preparation of tomorrow's LBOC meeting. The work is based on many earlier studies (LHC Report 123 by W. Chou and D. Ritson, and reports by H. Grote and F. Schmidt) and the experience with beam-beam in LHC Run 1.
She reminds us about the basic assumptions as used in the LHC design report at 7 TeV:  3.75 μm emittance, 142.5 μrad half crossing angle, and 9.42 sigma separation.
The criterion for DA in the presence of weak-strong beam-beam is that is should not be smaller than 6 sigma. In the presentation the DA from numerical simulations seems rather 7 sigma and this discrepancy with previous studies requires further investigations that will be made off-line.
In order to not limit the performance, a minimal requirement is make sure that the dynamical aperture (DA) including beam-beam remains larger than the physical aperture as defined by the primary collimators  (or roughly DA > 7 sigma, collimation at 6 sigma).
Tatiana discussed the tune footprints. The tune footprint for the 2012 LHC running parameters exceeded already the size of the nominal LHC footprint. Severe losses where observed in MD studies when the beam-beam separation was reduced below 6 sigma.
The parasitic beam-beam effects will increase with the number of parasitic crossing and are therefore expected to be more severe for 25 ns spacing than for 50 ns spacing. First test with 25 ns in the LHC were complicated by the presence of electron cloud phenomena and therefore not conclusive.
Strong-strong beam-beam simulations show that beam-beam effects can result in an increase of emittance and an over-population of tails.

A (full) crossing angle of 290murad for 2015 appears to be too tight. A crossing angle for 340murad should be fine for 2015.

IP BPM tolerances for HL-LHC orbit correction  -> MF (slides)

Miriam describes requirements for orbit correction for the HL-LHC in the high luminosity interaction regions and compares them with the present LHC.
For the HL-LHC, luminosity leveling will be applied also for the high-luminosity insertions.
She calculates the requirements in BPM precision to keep the luminosity loss below 5% (± 3.4 mum) and 1% (± 1.5 mum). Most important is the precision of the BPMS close to the IP. See the slides for details.

First thoughts on triplet BPM requirements for optics measurements in HL-LHC -> RT

Rogelio looked into the requirements of BPMs for optics correction in the HL-LHC. The BPM precision should be good enough to measure and correct beta-beating to the 5% level.

It will be very difficult to obtain a good precision for the small beta* at the IPs, the error on a 15cm beta* will be much larger than for a beta* = 60 cm. So far, beta*'s and luminosities at IP1 and IP5 were sufficiently similar.
For the HL-LHC, we may need beta* knobs to adjust and equalize beta*'s between IPs and the minimum waist positions at the IP. He expects that we will learn more on this already in the LHC Run 2.
Progress in BPM precision and reduction of calibration uncertainties can be expected from progress in electronics - new electronics has already been installed on some BPMs and will be tested in Run 2.

AOB 

Last update: 22-June-2014

MG & HB

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