Summary notes of the LCU meeting on 29/10/2007

Present: IA, MA, GB. RB, HB, RC, SF, MG, WH, PL, RT, SW, FZ

Report from meetings

• SLM -> MG
  Concerning the upcoming fellow committee: a prolongation was asked for collimation activities. There are also requests for CLIC and LINAC4. Further requests, like a fellow for beam-beam are not very likely to pass this time.
• ICC -> MG
  The leak in point 5 was fixed and cooling of sector 4-5 towards 1.9K resumed.

 Optics studies for high-beta configuration in IR1 and 5 -> Masamitsu Aiba (pdf file)
MA reported about optics studies using IR2 / 8 to recover losses of the vertical phase advances of 0.5 induced by using high beta optics in IP1 / 5. These studies are very encouraging. Starting from the injection optics, and using a single insertion, IR2 or IR8, it is possible to get +0.5 in vertical tune, at the constant injection beta * = 10 m and for alpha=D=D'=0 at the IP with good aperture. This could potentially allow keeping our standard tunes and injection and ramp optics also for high beta operation. It is assumed, that LHCb and ALICE would not take data in high beta running, which has to be verified with the physics coordinator.
SF suggested to check the tuning range of IR4 at collision (at injection it is limited by aperture considerations hat should not apply at top energy). Also, the option of changing the tune bt means of the main quadrupoles should be studied. Both scenarios will be considered by MA and presented in a future meeting.

First analysis of impact of longitudinal displacement of triplet quadrupoles -> FS (pdf file)
FS presented a first analysis of the impact of longitudinal displacements in the triplet quadrupoles.

These displacements are referred to as DY shifts by the hardware and alignment people. The largest such shifts are about 10 mm in IR1L, IR5R and 3 mm in IR8R. This would result in about 12% beta beating for the squeezed optics. Beta correction methods should allow to recover most of this. An LTC presentation will be prepared with contributions on the following topics:

• Beta-beating measurements with the aim of detecting the actual magnet displacement.

• Impact and feasibility of optics re-matching taking into account the measured longitudinal displacement.

• Evaluation of the impact on the squeeze process of the longitudinal displacement.

Review of noise requirements for LHC damper -> FZ (pdf file)
FZ presented estimates on noise requirements for the transverse LHC damper. His estimates are based on work of K. Ohmi and Y. Alexahin. The feedback gain can be adjusted to minimise the combined effect of noise from a limited pickup resolution and random kicks. For the nominal LHC transverse feedback performance, the expected emittance growth would be only about 2% per hour. If confirmed, this would be probably similar to or smaller than other noise sources like rf noise and could allow to leave the transverse feedback on in collisions.

The computations presented refer to a model in which two beams are present and hence the beam-beam effect is the dominant effect. The derivation should be re-done in the presence of a single beam, only and nonlinearities, which is the situation at the beginning of the flat top.

Chromatic beta-beating and performance of the collimation system -> CB
Postponed to the next meeting.

AOB
We will return to our normal 2 weeks cycle starting with a meeting next Monday.

Last update: 5-November-07

MG & HB

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