• Follow-up of actions from previous meetings
  • LHC optics news and modifications -> MG, HB, TR
    • MG reported that due to a very bad geometry of an SSS magnet allocated at Q11R7, the aperture tolerance was exceeded (n1=6.5) especially because of the high dispersion at this location (d=2.6m). TR provided a solution giving up the phase advance constraint in order to diminish beta and dispersion (also for IR3). An SSS with equally bad geometry will come soon to MEB for approval and probably a similar action will have to be taken.
    • HB and TR reported that Angeles Faus-Golfe produced a thin lens optics file for the TOTEM optics, but the optics is not exactly matched in the arcs. TR will try to rematch the optics accordingly
    • TR reported that he is working on the new version of the optics V6.501. The thin lens version revealed a problem of high beta function in IR6 (700 m), which probably existed also in old version as it was not properly optimized. RA asked if this version is approved and TR replied that the sequence file is not ready and a presentation will be made in the future indicating the applied changes (IR3, IR7 aperture issue mentioned above and the impact to IR4).
  • Web pages for V6.500 optics -> JJ (pdf file)
    • JJ presented the new optics version web-pages. New features have been added to the main page (e.g. hierarchy), the configuration pages and the table of contents (e.g. spreadsheet output). New features will be added for survey and aperture.
• Report from meetings
  • MEB -> SF
    • The board continued the work of discussion and approval of several magnets including dipoles, SSS, SpSSS and insertion quads (IR5 left completed). In the future, MQW and MBW will be discussed.
    • Some Q9 magnets (assembly with MQ and 2 MQTL) with very bad geometry have been produced (beam tube variation from -1 to +1.6mm). By chance there is no major aperture limitation but a follow up of the assembly procedure seems necessary. RA remarked that such aperture changes may influence the shower effect on the halo losses and a  FLUKA simulation should be done to see the impact. SF stated that if this is a limitation a magnet by magnet survey should be made. MG questioned if the collimation team should be part of the evaluation procedure. RA replied that this is not necessary, but it is good to check the effect (Action: MG, SR).
  • SLM -> MG
    • Hans Grote was appointed as honorary member of AB Dept. and he will continue helping on MADX.
    • The visit of a KEK collaborator was approved who will help with  LHC commissioning.
    • Following the HEP strategy group meeting in Zeuthen, the DG announced the CERN priorities for the future.
  • Collimation meetings -> RA
    • GB presented simulations for the optimized positions of the BLMs for ions. The number of BLMs still has to be discussed.
    • There was the monthly LARP video conference meeting for the phase II collimators. A new, more efficient work plan was put in place for Fermilab (N. Mokhov), including quench limits and backgrounds for IR5. Initial simulations showed that the TCT may become radioactive in IR5 and shielding may be needed but more work is necessary to fully confirm this. SLAC made a prototype for phase II.
    • A proposal for a collimation R&D project with European funds (40ME) was initiated. First it was rejected, but finally approved by the DG. It is the 3rd largest package from CERN and corresponds to 50 FTEs for 5 years (half from Europe)
• First results for collimation commissioning and error scenarios -> CB (pdf file)
  • Following the commissioning scenarios, more and more collimators are needed with increasing intensity
  • Loss maps show that phase I collimators cannot sustain nominal beam intensity and phase II collimators needed (30 additional)
  • Early commissioning scenario can be devised by using a simple two stage collimation using the tertiary as secondary, with two options: a) 10% of nominal with nominal optics b)  relaxing aperture of TCT and TCDQs by 1.5σ to get acceptable inefficiency level with β*=2m).
  • Error scenarios were studied where secondary becomes primary for any of the beams at injection and collision for horizontal halo.
  • For Beam 1, @ injection the highest peak is shifted from primary to secondary collimator as expected and in IR2 and 3 there is a 10-fold increase of losses. If losses are not taking place in collimators some areas get a factor of 100 higher (10 times above the quench limit). Equivalent features are present at collision (tertiary collimators act as secondary) and for Beam 2 (better at injection).
  • Simulations showed necessity of two-stage collimation and provide input to BI group for positioning of BLMs.
• Ideas on beta-beating correction -> RT (pdf file)
  • The beta-beating observable is the phase advance as "measured" in consecutive BPMs with standard FFT or SVD techniques from kicked turn-by-turn data. The correction circuit values are computed by solving a linear system with SVD.
  • Simulation ingredients include measured errors + Gaussian noise of 5 units for b₂ uncertainty, rms misalignments on the sextupoles (σ = 2 mm) and Gaussian noise in phase estimation to take into account BPM noise, decoherence and kick amplitude  (σ = 0.2^ο from analytical estimate). RA mentioned that an error due to a wrong setting in individual quadrupole may induce large beta-beating. RT replied that this can be included but this study is just to verify if the correction method works.
  • First results, indicate a peak beta-beating before correction of 70%, which drops to 15% after correction. The whole procedure needs maximum 5 iterations. Future studies will include several other effect (feed-down from b₃, quad tilt, etc).
  • SF mentioned that it is important to include the feed down effect from misalignment or orbit error on the sextupole spool pieces and to control also the dispersion beating. MG suggested to check the minimum number of correctors required (MIKADO approach).  RdM suggested to normalize with the corrector strength for having equivalent knobs.

• Advances on the MAD-X on-line model -> FS (pdf file)
  • Misunderstanding over the connection between the off and on-line model: they will be indeed connected but their purpose and tasks are different. Clear advantage of off-line model (MADXP) assignment of "true" thick element errors.
  • First milestone is ready: SDDS interface for MADX to be tested with CNGS commissioning. SR mentioned that SDDS may not be used by BPM, but tfs. WH replied that this is fully compatible with MADX.
• AOB
  • Relative survey alignment references in the SPS and the CNGS line -> WH (pdf file)
    • An alignment issue was found in the TT40/41 transfer line (CNGS but also LHC): it is 2-3mm above the SPS level. TR asked if this is an error propagated due to the different reference system of the two machines. WH answered that probably this is the case.
    • The effect is ±7 mm of orbit which cannot be corrected with present orbit correctors. The proposal, to be presented in LTC, is to shift one single quadrupole -1.2mm down, below the TT40/41 line, which compensate the offset and reduces the corrector strength to acceptable levels. As the optics fo rthe LHC transfer is not exactly the same, the impact of the quadrupole misalignment will have to be checked (Action: HB)

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