• Follow up of actions
• Report from meetings -> MG
  
  • Aperture review and related issues
    • After the e-LTC, a small working group chaired by S. Weisz was set up. Its mandate focus on the review of potential aperture issues due to non-conform installation in the field and the generation of the aperture model from the layout database.
      Potential aperture bottlenecks were identified in:
      • MKDs in IR6 for the non-deflected beam. An ECR announced a horizontal displacement of the vacuum chamber by 9 mm, which seems to be reduced to 7 mm: still to be confirmed, but potentially it is not an issue.
      • Spectrometer and its compensators in IR2 and IR8 due to a non correct longitudinal alignment. After verification TS/SU confirmed that everything is longitudinally aligned along the beam line, except the spectrometer magnet for ALICE (horizontal).
      • In the region of the single-beam collimators between the D1 and D2 in the experimental insertions. Interference between the bake out jacket and the other beam pipe induced a horizontal displacement of few millimeters. The bake out jacket was removed, thus improving the situation. the actual displacement is still to be measured accurately by TS/SU. Based on this the available beam aperture should be re-evaluated.
      • The alignment of the vacuum pipes in the MBW regions (were the protection masks are installed) is under discussion, as a vertical step of about 2 mm is visible.
    • For the time being, the automatic extraction of the aperture model from the layout database is still not completely available. The new sequence V6.503 is, however, in the debug phase (Thys is doing cross-checks). Then, it is hoped to get some date for the related aperture model to be compared with the one developed during the MEB activity.
      
• 5 TeV running conditions
  • Following the results of the hardware commissioning of the main dipole circuit in sector 4-5, it was decided to perform the full hardware commissioning of the next sectors to a level corresponding to 5 TeV, which will be the energy of the first run in 2008. It as also decided to perform special tests of the main dipole circuit in sector 5-6 to collect data concerning the required time to get to the nominal energy of 7 TeV. In this framework, the LHCCWG asked to compile a new set of beam parameters compatible with the new energy for the 2008.
    
    

• Minimum beta* for LHCb at 5 TeV beam energy -> WH (pdf)
  The question addressed by this presentation was raised at the LHCCWG.
  The scenario considered here, i.e., external crossing angle and 5 TeV, is rather pessimistic. Indeed, the present strategy for the LHC commissioning foresees to run the machine at a lower energy only for Phase A, i.e., without external crossing angle.
  Another important point to be considered is that, due to the pollution of the four TCTVs collimators to be installed in IR2/8, beta* will be very likely limited to 6 m during the 2008 run.
  For each value of beta* the crossing angle is maximised (compatible with available aperture). Under these conditions the minimum beta* acceptable in terms of aperture is 3 m. For beta*=2 m, the beam-beam separation is not enough as one encounter occurs at about 6 sigma. This means that until Phase B (corresponding to bunch spacing of 75 ns) also beta*=2 m is an acceptable solution at 5 TeV. It is important to stress that for beta*=2 m no aperture margin is available anymore.

• Revised pre-squeeze and squeeze optics for IR8 -> MM (pdf)
  The proposed optics solution from YP was optimised (reduced the number of steps for the pre-squeeze, smoothing of the actual beta-squeeze part) and the crossing scheme introduced.
  The variation of the strength of Q4 for Beam 1 is changing the slope during the squeeze: the impact on the squeeze time will have to be evaluated (with the help of PO).
  The overall performance in terms of beta-beating (with impact on the number of intermediate squeeze points) will have to be evaluated, too.

• Keeping MAD output tidy when mixing Fortran and C print statements -> JLN (ppt)
  A long standing issue is the MADX output due to the mixture of C and FOTRAN modules. Indeed, the way the output buffer performs in the two languages is different and flushing might not respect the actual order of the module calls. The proposed solution consists in adding a C wrapper to the FORTRAN modules so to make the output buffer behaviour uniform between the two languages. The wrapper will be added automatically by a perl script when Make is invoked.

• Status of the LHC online model -> IA (pdf)
  A number of demos were made before and after the e-LTC to show the main functionalities of the on-line model to the main users in ABP (for the time being). Due to a re-factoring on-going in LSA, currently the on-line model works on in the so-called expert mode, i.e., without LSA. A general presentation to LCU is expected once LSA will be back in production. The target date is the next LCU meeting.

• Status of the LHC beta-beating correction tool -> RT (pdf)
  Thanks to the last efforts, the beta-beating correction is currently interfaced to YASP, the on-line model, and LSA (not tested, yet). An important addition is a new algorithm for coupling measurement and correction, contributed by A. Franchi. the next milestone will be a series of MDs in the SPS to test the main functionalities.

• AOB

Last update: 11-Apr-08
MG

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