Summary notes of the LCU meeting on 04/09/2012

Present: RB, HB, RdM, LD, OD, SF, MF, MG, BH, JJ, EM, EQ, MS, MSt, RT, RV, FZ, PS

Report from meetings

• SLM and general information -> MG
  There will be vacuum beam pipe layout changes in IR2, IR8 to help with issues of rf-fingers. Elliptical chambers will be replaced by larger round chambers. Details will be described in an ECR.
  There will also be modifications on the bus bars of the main quadrupoles in points 1 and 5 to avoid refurbishing interconnects. This will imply cutting the bus bars at the level of the Q11. The situation could be put back in case of need.
  JJ informed us about the proton lead test runs planned next week.
  HB said that an about 24h high-beta run is planned for next week with the goal to find and establish collisions at beta of 1km in IP1&5.
  A short discussion on MDs proposed for next block: non-linear model at top energy (detuning with injection optics and triplet FQ with IR bumps); optics at 40 cm; the whole situation will be reviewed in the afternoon at the LSWG meeting.
• LHC Status -> BH
  The LHC is running well, with peak luminosities up to 7e33cm-2s-1. There are issues with heating of TDIs and instruments.
  The synchrotron light monitors (BSRT) are currently unavailable. For the up-to-date LHC status see the latest news.
• LMC -> FZ
  Frank reported form several LMC meetings. For details see the minutes.
  An action for ABP concerning the crossing angle at injection for IR8 has been mentioned. SF suggested to have a dedicated measurement at injection with the vertical crossing angle in order to assess the situation. This should be the basis for the scenarios to be studied later. MG will follow this up and organise activities.
• WP8, LBS -> HB
  Helmut said he was asked by Lucio Rossi to act as the WP8 leader for the HL-LHC with Daniel Lacarrere/EN-MEF from the hardware side as deputy. The work package 8 deals with the Collider Experiment Interface for the HL-LHC and can be seen as extension or link of existing working groups (LEB, LTEX, LBS, ColUSM) to follow up any changes in the straight sections with the dispersion suppressor region included, which are of relevance to the experiments.
  There was a smaller LBS meeting in August, mainly as preparation for the next meeting in two weeks, which will discuss the plans for a tighter VELO in LHCb and the ALICE background issue connected to the TDI heating.
• MAD-X status -> LD
  A paper describing the future plans for MAD-X can be found on the web-site. The documentation was restructured. Laurent asked module keepers to do tests, and received little feedback so far. A new development version of MAD-X will be released soon.

Understanding the octupole feed down in the LHC -> EMcL (slides)
Ewen presented a study aiming to understand the feed down effects of the LHC Landau octupoles.
He looked at the observed and expected changes of tune, chromaticity and coupling by changing the octupole strengths in the LHC. As an example, ramping down the octupoles from 450A to 50 A may change Q' from +6 to -2.

He tried to account for the parameter changes in terms of feed down effects due to closed orbit and mechanical misalignment. Tables with numerical values for the observed and expected effects are given in the slides. The changes in chromaticity are found to be in broad agreement with the expectations. Tune and in particular coupling changes appear to be larger than expected.
SF said that the multipole errors of the octupoles are known and should be included. In particular the a2 and b2 components may be rather significant and have a direct impact on coupling and tune variation. It was also proposed to check the effect of off-momentum combined with the very large Q''. Also, the mechanical offset of BPMs is questioned and it is mentioned (e.g., it is not known at cold) that a systematic vertical offset between the mechanical and magnetic axis has been observed. Hence, it does not seem to be advisable to use the data concerning the mechanical misalignment in the vertical plane.

Last update: 04-September-2012

MG & HB

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