Summary notes of the HSS meeting on 12/05/2014

Present: HB, RDM, LD, SF, MF, SG, MG, JJ, AK, DM, MM, GR, AS, MS, PS, RT, GV, RW

Report from meetings

• SLM and general information -> MG
  There has been no recent section leader meeting. Massimo informed us about planning for the May associate and fellow committee (AFC). Quotas are tight and we plan for several committees ahead.
  Massimo attended the HL-LHC US-LARP meeting last week in BNL. The collaboration goes well, no major surprises.
  In the next HSS meeting Tatiana will make a presentation on beam-beam and crossing angles. We will also discuss BPM specs for the triplet.
• MAD-X status -> LD
  A MAD-X meeting took place last week. Corrections and bug fixes were discussed and are being implemented for the next development release.
  Ghislain found bugs in the sequence expansion. In case of doubts, seqedit + flatten can be tried as workaround.
  Another meeting is planned in 3 weeks.
  The physics to implement thick dipoles is available, more checks (bv flag) sand fixes in the context of bends are required.
• SixTrack status -> RdM
  The effect of the bv flag, is reviewed, in particular in the context of cavities. More work on beam-beam relevant for flat beams is required.
• PS-studies -> SG
  Simone reminded us that injectors re-start soon, and that a meeting on space charge will be organized at CERN next week.

Cleaning and IR7 optics  -> DM (slides)

As discussed previously, the IR7 optics will be modified as required to power down some MQW in order to increase the number of spare magnets. This should take place during LS2, but studies concerning the performance of the novel optical configuration (provided by Thys) has been launched already. The first validations studies highlighted a worsening of the cleaning efficiency, with changes in loss locations around IP8 were observed in tracking, related to off-momentum particles generated by single diffractive scattering in collimators.
Daniele compared several optics alternatives, in which the dispersion function was gradually restored to its original value, including also the phase advance over the insertion. The studies showed that it is indeed possible to restore the original performance. They also indicate that the non-periodic dispersion plays an important role for single-pass losses.

Analysis of differences in SLHCV3.1b and HLLHCV1.0  -> RdM (slides)

Riccardo discussed changes in dynamic apertures for the HL-LHC due to the orientation of the triplet quadrupoles.
Indeed, depending on the orientation of the various magnets compensations of some multipoles will occur.
This is shown by enhancing the strength of the systematic multipoles and by checking the resonance driving terms and the strength of the non-linear correctors.
Correspondingly, DA studies for the various configurations have been launched. The difference seems negligible and hence no change with respect to the current orientation, driven by hardware considerations, will be asked. The most critical regions are the new triplets. Several optics versions and alternatives of powering quadrupoles on the lead or non-lead sides were considered, see the slides. Some options would require rather strong multipole corrections.

Towards collision tunes at injection -> RT (slides)

Rogelio reviews the arguments in favour of the use of collision tunes since injection. He also reminds the MD results, which confirm that this change would not have any side effect.
The current proposal aims at using the collision optics since injection, with the MQTs used to set the tunes to the appropriate values. This would generate flexible configuration. Studies have been performed to assess the induced beta-beating in case MQTs would be used and it turned out that it is negligible even in the case of an ATS-compatible optics.

AOB 

Last update: 24-May-2014

MG & HB

Back to HSS Minutes