Summary notes of the LCU meeting on 17/09/2013

Present: RA, FB, RB, HB, RdM, LD, OD, SF, MHF, MF, MG, JJ, ALat, LL, GR, BS, MS, RT, RV, FZ

Report from meetings

• SLM and general information -> MG
  Three students will be requested at the current selection committee for our group, two of which will work for TLEP.
  For the coming fellow selection committee, we foresee to select a replacement for Frederic Bouly who leaves at the end of this month. There will be also an attempt to get additional fellow positions for ABP.
  The presentation of Roderik in the last meeting was followed by further discussions in WP2 to converge on realistic parameter sets including Delta p/p for tolerances. Another subject discussed in HL-LHC working group meetings was the modelling of magnetic fields for the new large aperture quadrupole and dipole magnets, with the aim to also simulate the non-linear parts based on symplectic integrators.
  Massimo reminds that in case of accidents, and in particular professional accidents which include traffic accidents on the way to and back from work, both the EDH and HS50 forms should be filled in to inform both the department and health assurance.
• Collimation status -> SR
  Stefano said he will make a presentation in the coming LMC meeting on the outcome of the collimation workshop and on the production for LS1.
• LBS -> HB
  Helmut said that yesterdays LBS meeting had presentations on electron cloud build-up in the inner triplets by Giovanni Iadarola and on tracking studies for the HL-LHC by Frederic Bouly, and that the showed a slide with links to the three upcoming HL-LHC related workshops this year. The slides are on indico.
• MAD-X status -> LD
  Laurent said they are setting up the Mac mini server for regular testing of MAD-X and that a new pro release can be expected in the coming 2 weeks. The server should also be useful for SixTrack.
  Andrea Latina is going to implement thick dipole tracking.  
• SixTrack status -> RdM
  Riccardo said that there have been issues with BOINC and that he has no major news to report otherwise.

Optics aspect of PIC and US1 scenarios for HL-LHC  -> MF (slides)

In addition to the full upgrade, which is referred to as US2, we were asked for the upcoming workshop RLIUP to also look at two reduced scenarios, namely:

PIC (performance improvement and consolidation) and US1 (upgrade scenario 1). The triplets in IP1 and IP5 will be replaced in any of the three scenarios under consideration. A long discussion took place about whether the three scenarios should be considered as part of a staged approach or as independent alternatives...
Crab cavities are only included in the full upgrade scenario. Miriam looked at the round and flat beam optics at injection, pre-squeeze and squeezed, for these scenarios. Going to a larger triplet but not changing most of the straight section as considered for the PIC would lead to a situation in which the TAN would be the main aperture limit unless it is also modified.
The aperture could be optimized slightly just by centering beams in the TAN using the MCBX correctors. Modifying also the TAN and beam screen would be beneficial for the reduced upgrade scenarios.
Massimo suggested to always specify which emittance and crossing angles and tolerances were assumed for any discussion of available and required aperture in terms of n1.

HL-LHC TAN aperture with reduced tolerances -> RA (slides)

Reyes looked at the upgrade scenarios with flat and round beams assuming a new TAN with RECTELLIPSE shaped geometry of 41mm/37mm RECTELLIPSE opening. As also observed in energy deposition studies by L. Esposito and F. Cerutti, the new TAN would be much less effective in absorbing the neutral particles generated in the collisions than the present TAN. Using the reduced tolerances presented by Roderik in the last meeting and both 2.5 and 3.5 murad normalized emittances, she calculated the apertures in terms of n1 for the new geometry and what would happen if the aperture would be reduced by 10, 20 or 30%. She finds that a 30% reduction would result in a TAN aperture which is tighter than the Q2. Flat beams (beta*=7.5 cm) are more restrictive than round beams (beta*=15 cm).
It is worth stressing that changing the emittance and using expected values is not correct as not all components included in the aperture estimates scale with emittance, e.g., the orbit contribution. Stefano suggests to present the views of Helmut at the collimation WG and/or MPP for feedback. Massimo approves this proposal.
Overall, the results show that the original specification of the TAN aperture is optimal and there is no margin for reduction.
Stephane proposes to check what would be the gain in the efficiency of the TAN in case it would be located just next to the IP-side of the D2 separation dipole. Riccardo replies that some new configurations are under consideration by the FLUKA team.

AOB 

None

Last update: 23-September-2013

MG & HB

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