Summary notes of the LCU meeting on 21/09/2010

Present: CA, HB, SF, MF, MG, JJ, YL, TM, MS, RT, GV, SW, FZ

Report from meetings

• LMC -> FZ
  FZ reported from the LMC last Friday. The subjects included tune-meter and damper interference, progress in the LHC commissioning with crossing angle, news on the "hump" and the first observation of elastic events by Totem. For more details see the LMC minutes.
• Heavy Ion -> JJ
  John reported from several meetings and a conference which he attended in the context of the upcoming Heavy Ion (HI) run in the LHC. His commissioning plan was approved. The crossing angle will be adjusted to zero in all collision points. Details on the filling schemes for HI-operation will be followed up in the LPC. The afternoon of this Wednesday (22/09/10)  LHCC is dedicated to a discussion of the HI run.
• LBS -> HB
  The LBS#18 meeting was held on the 20. September. There were two presentations from ALICE, one on the comparison of background observation with predictions and the other on machine induced high voltage trips in the ALICE detector.
  There was a presentation on the crossing angle measurement using the CMS ZDC, the zero degree calorimeter installed in the TAN. The meeting ended with a discussion of backgrounds for HI-operation.
• LEB and general information -> MG
  MG attended a meeting of the LEB (LHC Experimental Beampipes Working group). The experiments have now very good data on the position of the beam pipe and other material in the beam pipe region from secondary interactions in the material. The aim is to improve on tolerances and alignment to allow to decrease the beam pipe radius in the central region by several mm by 2016 (ALICE) or later.
  Global apertures (equivalent to determining the minimum n1 over each ring) were measured in the recent commissioning with crossing angles and found to be significantly larger than estimated using n1. This can be attributed to the orbit, alignment and beta-beating tolerances which are well within and in some cases significantly better than the LHC design specifications. The subject will be further followed up also in a more general context than the LEB.
  There is also data from the SU section on tilt misalignments (mostly triplets in IR5, 8), which could be reduced by remotely adjusting the triplet positions.  
• Online Model -> CA  (slides)
  Carmen showed which models (thin, thick, w.o. errors) are available. Several options to run Mad-X and display results are available.
  Gabriel Müller gave a presentation last week on what is available in the CCC. Beam and aperture positions can be displayed. This was used in the recent aperture measurements. Feedback and further suggestions of what would be useful to calculate and display are welcome.
  MG after discussion with FS proposed to have fixed screens to display optics and aperture over the ring during the cycle.

SLHCv3: first results on optics, chromatic properties, long term stability: part II -> RdM (slides)

RdM gave the second presentation on the LHC optics upgrade plans.
He showed the size of the tune footprint from optical imperfections at low beta*. As shown last time, the new scheme involves the neighboring insertions IR8 and IR2 for IP1,  IR4 and IR6 in IP5 to reach lower beta* in one transverse plane while keeping the chromatic aberrations corrected. This new scheme implies larger-than-nominal betas in the arcs. The size of the footprint could be reduced by using a more symmetric sextuple correction scheme based on even numbers of sextupoles. This could be reached by adding an extra sextupole or by short circuiting one existing sextuple.
He also showed tracking results with  dynamic aperture determinations which will also be used to specify the field quality for new magnets (D1, D2, Q4) required in this scheme. These studies enable selecting among the configurations with alternating crossing planes (preferred) and non-alternating crossing plane (worse DA). The addition of one sextupole also improves DA.
RdM also showed the tune footprint from the beam-beam interactions in IR1&5 in this scheme with 21 parasitic interactions on either side of the IPs.
RC and HB suggested to consider also more generally the re-optimization of collision tunes and longitudinal beam parameters (bunch length, Dp/p).
A number of items will be studied in order to complete the performance assessment of this new scheme. In particular, a list of MD studies to be performed on the nominal machine should be prepared.

AOB

None

Last update: 21-September-2010

MG & HB

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