Summary notes of the LCU meeting on 21/08/2012

Present: JA, HB, SF, RdM, RT, MS, RB, MG, OD, EMcL, RV, EQ

Report from meetings

• SLM and general information -> MG
  Request to change the vauum layout in point 2 (right) and 8 (left) in the framework of replacement of the VMTSA module (featuring failing RF fingers). Aprerture verifications are in progress.
  No need to move the y-shaped vacuum chamber in point 8 for TCT installation.
  Request to shorten the bus bars of the QF/D main circuits in points 1 and 5. This might have impact on future instllations (no possiblity to have quadrupoles in serios with the main quads downstream of Q11). Consequences will be looked at.
  Discussions on AFP experiment are planned at the next LEB meeting.
  HL-LHC: a request to fill in the time sheets has been circulated to all people involved in the upgrade studies (HiLumi part). Details still need to be sorted out: filling these forms should be started only after green light from the project management.
  Polarity check of several circuits by RT and team: MCOs fine; MOs found correct with a potential issue for circuit ROD.A23.B1; the two MSSs circuits tested feature a wrong polarity.
• LHC status -> BH
  New luminosity record: achieved 7E33 cm-2 s-1 and even more.

Chromatic effects due to off-momentum operation for p-Pb at 4 Z TeV -> RV (slides)
Reine presented a new study of correction of the chromatic beta-beating. In the case of p-Pb collisions the two beams will be circulating with an energy offset, which will create chromatic effects. If the baseline is assumed to be IP1/2/5 at 0.6 m of beta* and IP8 at 3 m, then increasing IR1/2/5 beta* to 0.8 m would reduce the chromatic beta-beating by 30%, while decreasing IP8 beta* to 2 m would have a negligible ipact on the chromatic beta-beating.
An analytical approach has been developed and compared with a numerical one based on the tools by RT et al. showing good agreement.
The correction could be implemented in the squeeze, but is not needed from the very beginning, but rather when beta* is 2 for IP1/2/5 and around 3 m in IP8. The correction will be in the form of a knob, i.e., easily implemented in LSA.
Similarly, chromaticity can be corrected and the effect of octupoles (due to feed down) has been evaluated, thus allowing a compensation.
It is suggested to verify the impact of the proposed correction on the dispersion function. Furthermroe, it is pointed out that a re-matching of the insertions would solve at the roots the chromatic beta-beating.

Last update: 24-July-2012

MG & HB

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