Summary notes of the LCU meeting on 05/05/2009

Present: HB, MG, WH, BH, EL, FR, AR, GV, SW, FS

Report from meetings

• SLM -> MG
  MG reminds that he circulated an email on "On-line safety courses" and the we are encouraged to follow these.
  An ABP Forum is planned on alignment, with three presentations from members of the SU section showing the results of the recent alignment campaigns for the different machines (CPS, SPS, and LHC).
  MAD-X polarity flag is being reviewed with SF, FS, TR, MG, and specifications transmitted to Pascal Leroux, Stephan Russenschuck, and Markus Zerlauth for implementation in the layout database. While the currently implemented polarity flag was found correct for quadrupoles (MQTLs, and MQTs) there are still open questions concerning the higher order multipole correctors for the triplet magnets and skew magnets.
  There is a request for volunteers to help with access and patrols in the LHC: everybody is encouraged to enroll.
  TR retired as CERN staff and stays as honorary member. Olav Berrig is now in charge of the LHC optics files.
  HB said there have been discussions in preparation of the planned tests of ramping down the separation bumps to minimize the time needed to bring beams into collisions. The idea is now to do these tests in several steps, starting with hardware tests and measurements of the MCBX and MCBY, MCBC magnets alone and more complete combined tests later.
  The MCBX are nested and it is not completely clear to which extent current limits can be translated into strength limits in one plane.
  After the meeting BH discussed with K. H. Mess and W. Venturini and collected some more information:
  1.) There is a quench limit for these magnets. As they are nested coils the overall quench limit depends on the current in both, the hor. and vert. coil, namely
  I^2 (MCBXH) +  I^2 (MCBXV) <= I^2 total  
  Where the limit of I total is 550 A.  
  2.) The solution currently implemented consists of limiting both coils to 70 % of Itotal current. A better solution should be found as this limit is too severe.  
  3.) Persistent (or eddy) current effects are present only when the currents are low. The experts are working therefore on a better description of these coils for the FiDel. This is a principle issue and any change of current in these coils will lead to a small orbit distortion in the other plane (if the overall field created by the two coils is small)

Studies for the IR8 squeeze -> WH (pdf)

WH explained recent work on the IR8 squeeze computed by Malika. This is done taking into account all known hardware constraints and the prospects of the first longer LHC operation for physics at 5 TeV. In the earlier operation, it is planned to allow for a squeeze in IR8 from 10m down to 2 m to increase luminosity.
Intermediate matched optics were computed using steps of 0.5 m in beta*. The computation show that even using 1 m step the maximum beta-beating and chromaticity variation in between two matched points is small. The only exception is the transition between beta* = 6m and 7m and between 3 m and 2 m. A reason for reducing the number of matched optics during the squeeze sequence is the time for the squeeze sequence (the currents are rounded before and after each matched optics).
However, after the meeting MG got the information from Marek Strzelczyk that the squeeze time for IR8 (including pre-squeeze) is about 1300 s which is compatible with IR1 and IR5 time. Therefore, there is no real need to reduce the number of matched optics form the squeeze sequence.

WH also said that the crossing schemes were defined for the nominal LHC but will have to be reviewed for 5 TeV and the beta* values planned for the first LHC run. For this it will also be important to clarify the MCBX limitations (knowing that another possibility would be, e.g., to share the strength among the MCBX in Q1 and Q2).

For IR2 in proton operation no squeeze is required as the luminosity has to be low and this can be achieved by displacing bunches (up to 50 ns bunch spacing).

AOB

FS reports that a new MAD-X version will be released soon to overcome a number of issues. The new compiler provided an interesting gain in speed.

Last update: 05-May-09

MG & HB

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