Summary notes of the LCU meeting on 15/01/2008

Present: IA, RA, GB, RB, HB, RDM, MG, JJ, PL, MM, TP, VP, SR, TR, FR, FS,  RT, TW, SW, FZ, JN

Report from meetings

• ICC -> MG
  Following a request by Steve Myers, there were presentations in yesterdays ABMB by the groups on the present status of hardware for the LHC. For the OP and ABP groups the presentations focused on the organisation of the LHC commissioning.
  There will be ATC-ABOC days from 21-23 January. Feel free to participate if you are interested, just make sure to register here.
  One large aperture vertical orbit corrector MCBY next to Q5 in IR4 is not working (short in the coils). It is not yet known if this can be fixed. This will be further investigated and reported to the LTC. There is no obvious replacement and we may have to consider to run without this corrector.
  MG introduced Jean-Luc Nougaret, previously in AB/CO. He is now in our group, initially for 6 month, to work with FS on Mad-X.
  MG said he had followed up on the issue of the minimum size of the internal spectrometer bumps in IR2 and IR8, a subject which came up in a recent LHCCWG meeting. As far as power convertors are concerned, there should be no problem to cover the full dynamic range to ramp at constant bump size.

Follow-up of potential issue with TCTVB in IR2 for ions -> RA (pdf) & JJ (pdf)

As reported in the last meeting, there is the issue of partial coverage of the ALICE ZDC acceptance by tight TCTVB collimators settings. This was followed up by RA and JJ. RA said that the TCTVBs are not absolutely required for ion operation, but are still expected to be useful. He proposed to open the TCTVBs from nominally 7.8 mm in proton operation to 13 mm for ion operation. This would still give a 3 mm margin for the triplet protection.

JJ showed the aperture, beam envelopes and and neutron angles in IR2. The acceptance also depends on the crossing angle. Some ALICE estimates have been done for 100 microrad crossing angle. For heavy ion operation, relatively small crossing angles of about 10 microrad should normally be sufficient. To be further follow up.
Action JJ, communicate maximum crossing angle (40 microrad) to ALICE.

Recent beta-beating studies during squeeze -> MG (pdf)
The subject of beta beating during the squeeze has been discussed previously with presentations in LHCCWG and LTC. The number of intermediate points during the squeeze was found to be adequate for the proposed solution for IR1/5 with variation of the optical parameters (tune, beta-beating etc.) well within the normal budgets. This is now reviewed taking into account the measured longitudinal misalignments of the triplet magnets. The largest misalignment of about 17 mm was found on Q2.R5. The longitudinal misalignments generate tune shifts and to some extend also beta-beating as a function of beta*. The effect is small for the beta* values used at injection and the beginning of the squeeze. It becomes rather sizeable below a beta* of about 4 m and will require rematching in IR1,5. SF already provided a new solution for IR1/5 rematched including the measured longitudinal misalignments at beta* =0.55 m. It is planned that these results will be part of the LTC presentation concerning the situation of the impact of the longitudinal misalignment of triplets by FS.
As far as the squeeze solution for IR8 is concerned (provided by YP), further work is also required.  The change of optics is made in two steps: i) the triplets are lowered from 220 T/m to 205 T/m (nominal value), ii) beta* is decreased to 2 m. beta* is left floating during i) and then the squeeze starts. This implies that at the beginning of the squeeze proper a large beating is observed. Then, in the region around 3 m (Beam 1) improvements should made, probably by adding one more point.

AOB
None.

Last update: 15-Januar-08

MG & HB

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