Summary notes of the LCU meeting on 13/01/2009

Present: MA, RA, HB, RDM, MG, WH, JJ, JM, JN, TP, RT, TW, SW, YS, FZ

Report from meetings

• SLM and general information -> MG
  Emanuele Laface was introduced by MG and WH. EL will work on beam-beam (for both the nominal LHC and the upgrade scenarios), supervised by WH.
  MG reported about follow up in the context of optics for the LHC upgrade. It was decided to freeze an upgrade study optics beginning of March, and to use this for tracking (DA and beam-beam, the latter under the responsibility of WH) and collimation studies. SF is in charge of upgrade optics studies (in collaboration with JM and B. Holzer) and their co-ordination within LCU. SF will report regularly the progress at this meeting and dedicated presentations will also be given by the people contributing to the studies. More specialized meetings between the people directly working on this will be organized in addition whenever needed.
  MG said that polarity discrepancies between Mad-X modeling and hardware settings during the first days of beam in the LHC were reviewed and clarified. After the 11 September (19:27), there was only one single sign-discrepancy on Beam 1. Everything was found consistent on Beam 2 and therefore sign errors are excluded as the main source of the observed beta-beating.
  We received information on the observed stray field of the CMS magnet. Discussions with S. Russenschuck have been launched to understand the possibility of simulating such a stray field. Possible consequences for us are followed up by YS, FZ and MG (with additional support from SF, FS, RT, B. Dalena).

Study with one global crab cavity at IR4 for the LHC Upgrade -> YS  (pdf)

YS reported about studies using a single crab cavity. Crab cavities have been considered for the LHC upgrade as a mean to compensate for the luminosity loss due to the geometrical factor induced by the crossing angles. To test the feasibility of crab cavities in the LHC, it has been proposed to start with a single crab cavity (hence affecting one beam, only) and to see if it could already induce a visible effect on the machine performance.
The main purpose of this study was to check on a possible interference of the effect of a single cavity on the beam and momentum collimation. For these studies, YS assumed a single 800 MHz cavity in IR4 which would tilt Beam 1 such that it would be crabbed in IR5. This implies that the effect is small (Beam 2 is not crabbed), but also IR1 features a "wrongly-crabbed" Beam 1.
The net effect is a gain of 5% luminosity (normalizing to 10³⁴ cm² s^-1) in IR5 and a correspondent loss in IR1 loss from crossing angles at a beta* = 0.55 m. In the case of beat*=25 cm the impact is larger about 70% luminosity increase in IR5 (normalizing to 10³⁴ cm² s^-1).
Tracking studies with a crab cavity were performed. DA aperture is reduced by 2-2.5 sigmas (but it is computed using two seeds, only).
Loss maps were also computed, comparing them with the situation for the nominal LHC at collision. Two situations were considered depending on the cut applied in the generation of the longitudinal distribution of impact parameters. RA stated that the generation of impact parameters is rather delicate. Hence, the results presented should be considered as very preliminary ones. Further work with help from the collimation team will be required before any definite conclusions can be drawn.

AOB

None

Last update: 16-January-09

MG & HB

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