Summary notes of the LCU meeting on 07/10/2008

Present: MA, RC, SF, MG, NH, JJ, YL, AM, JLN, TP, SR, TR, FeRo, FS, RT, SP, SW, TW, FZ

Report from meetings

• SLM and general information -> MG
  
  • According to the latest news, there will be a Chamonix meeting in March next year.
  • The 2008 physics run will be shortened. The LHC injector complex will be ready to deliver the beam to the LHC by beginning of May 2009.
  • The decision concerning whether there will be a ion run in 2009 will be taken by the SPC in its November meeting.
  • MG reviews briefly the on-going activities:
    •  
    Polarity checks: the logic found by SF for quadrupoles was confirmed by S. Russenschuck. He will check the situation for skew and higher order magnets and will also cross-check the polarity flag in the sequence.
    • Aperture: the cross-check of the new file with vacuum markers is finished. the markers do not cover the region of about 15-20 m around IP1/5, but for IP2/8 they cover down to about 1 m from the IP. A number of issues were found. Samy and Pascal were informed and feedback is awaited. The file with mechanical tolerances is also being reviewed.
    • Scripts for simulations: a new series of scripts for performing coupling and triplet corrections have been prepared by SF. Among other things, they automatically detect the beam type.
      

Proposed changes for the aperture module -> TR  (pdf)

A number of changes in the aperture module are proposed by TR based on the experience of the past months. Here is the list of the agreed changes:

• The names of the tolerance values listed in the Twiss table (presently called APTOL_1, APTOL_2, APTOL_3) will be replaced by RTOL, XTOL, YTOL as in the aperture table.

• The format of the offset files will be changed to TFS format where the first entry specifies the reference element. It is considered an additional advantage to be able to override the name of this reference element in the parameter list of the aperture command.

• In a second stage, the name of the X, Y columns in the aperture table (representing the aperture offset and not the beam trajectory as in the Twiss table) should be changed too, to avoid confusion.

A number of features were observed mainly linked with zero-length elements (markers). Sample jobs were prepared and JBJ will verify the situation in the coming weeks.

Follow up of LHC thick model with errors -> FeRo  (pdf)
FeRo described the recent results concerning the filed errors to thick elements using PTC.
A successful comparison between MAD-X (thin) and PTC was carried out including b2 errors in the dipoles. A new version of PTC with improved error management was prepared by FS: it will be tested soon.
The new scripts prepared by SF were also studied, in particular the proposed correction of the b2 error in the dipoles by means of the MQTs. The phase error along s is nicely corrected. The induced beta-beating is small. Hence, this approach could be proposed as a standard setting for the beam commissioning. The b2 correction should be incorporated in FiDeL. SF comments that another advantage would be to have the MQTs working at about 6 A, hence outside the region around 0 A where the transfer function is essentially unknown. In principle, the additional beta-beating might be completely corrected by re-matching the insertions. However, this would mean having an time-dependent optics as the matching should follow the variation of b2 within the cycle. This is considered not worth it.
The correction of the coupling due to a2 errors is also tested, in particular in view of assessing the impact of the potential  missing skew quadrupoles in the Q23.R3 and Q27.R3 (to be replaced with spare without the appropriate corrector packages due to the recent incident) on the correction quality. The analysis should be completed.