• Report from meetings
  • MEB -> MG
    • Presentation and approval activity continued for SSS and S4.
    • Today the injection septa (MSI) will be presented.
    • Continuous pressure on the SSS due to installation for off-line approval.
  • FQWG ->  SF, MG
    • Meeting on field quality of MQT/MQTL (minutes are available here)
      1. Assessment of field quality of MQTL was made using MQT targets instead of target error table for MQTL based on mechanical tolerances.
      2. Tracking campaign by MG showed 1σ reduction of DA @ 45^o but still above 11σ, in the presence of feed-down from b₁₀ due to the closed orbit of 4 mm.
      3. Field quality is known only at warm and preliminary results show discrepancies with cold measurements. A warm to cold correlation has to be provided for further studies.
      4. Yannis informed that V. Remondino provided all corrector measured data for production of error tables based on measurements and further actions when errors are out of tolerance.
    • A brainstorming discussion meeting was held for the field model from measured harmonics for the LHC control room (details are available here).
      1. Talks by L. Bottura on FIDEL, R.Wolf on LEP experience, MG on what we have available and need for MAD-X, M. Lamont on ELSA.
      2. There are still no misalignment effects in the control system.
      3. A meeting will be held tomorrow to sum up the results of the discussion.
    • This Friday a meeting will be held on the measurement programme of insertion magnets.
  • MAR Workshop -> SF  (details are available here)
    • A workshop dedicated on magnet reparation during LHC operation.
    • Proposal to have a full production line at CERN (1 building or several) but no decision yet made.
    • Criticism by P. Limon (FERMILAB) who thinks that only a cryo- decryo- facility is sufficient.
    • Some conflict may exist with respect to the location of this facility and future projects, e.g. building 181 and the option of having a new machine in the ISR tunnel.
    • A follow-up meeting will take place in the near future.
• b6 budget in the LHC quadrupoles -> SF (pdf file)
  • Overview of the b6 hysteresis effects at injection for MQM and MQY
    • Very low current of MQM and MQY induces a very negative b₆ (-20 to -25 for MQM, -6 to MQY) and very large b₁₀ depending on injection current, critical current and minimum current after ramping down.
  • Comparison with MQ’s
    • Detuning
      1. MQ detuning from systematic b₆ of -2 units is ΔQ~5.10^-3@ 12σ  (margin  to be redistributed to the other quadrupoles as measured MQ <b₆> ~ 0).
      2. Total detuning from other quads similar to above margin (main contribution comes from MQM and MQY).
    • Driving terms
      1. Most important C_(0,6) due to resonance proximity.
      2. MQ contribution to C_(0,6)~400 due to random b₆ of 1.75 units (systematic is almost canceled due to π/2 phase advance).
      3. MQTL and MQX comparable to MQ contribution (C_(0,6)~500 for each), but MQM and MQY much bigger ((C_(0,6)~1500 and 2500 respectively).
      4. The total contribution for all insertion magnets is an order of magnitude higher than for the MQ (C_(0,6)~3500).
  • Conclusions and future plans:
    • Main contribution to b₆ comes from the MQM/MQY magnets inducing amplitude detuning of the order of 0.005 at 12σ and exciting C_(0,6) (1 order of magnitude larger compared to MQ contribution).
    •  DA tracking studies needed (MG) to fully assess the impact of the b₆ (and b₁₀) hysteresis effects in MQMs and MQYs.
    • Possible cures are foreseen (driving term correction with MCTX triplet corrector magnets and/or dedicated cycles for each MQM/MQY magnets for magnet to magnet self-compensation)
• On-going discussions concerning high-beta options in IR1 and IR5 -> MG
  • A meeting was held between Karsten Eggert, Ernst Radermacher, Valentina Avati from Totem and Massimo Giovannozzi, Werner Herr, Helmut Burkhardt from LOC.
  • Options and possible running scenarios for high beta optics were discussed:
    • High beta (> 1000 m ) optics: The phase advance for the high beta optics is very different from the standard optics. The reduction corresponds to roughly 0.5 in vertical tune for a single insertion. Optics files with beta* = 1540 m are available and have been documented in LHC Project Note 369 by André Verdier. Tunes were matched assuming simultaneous high beta operation in both IR1 and IR5. Atlas proposes their own version of files with high beta* = 2540 m.  The reduction in phase advance is comparable to the Totem case and simultaneous operation of the Totem and Atlas high beta optics should be feasible. Compared to the standard optics, the vertical tune is lower by one unit, with about Qy = 58.32 rather than Qy = 59.32 in case of the standard optics. Dedicated high beta injection, ramp and squeeze files and commissioning will be required and the aperture available at injection will be less than in the standard case.
    • 90 m optics for Totem: The LHC will be commissioned with the standard physics optics (Qx = 64.28, Qy = 59.31) and a beta* of 17 m during injection and ramp in IR1 and IR5. For early physics operation, the number of bunches will be limited (43 or 156) and the intensity per bunch will remain below 5 10¹⁰ p. The beta* will be squeezed down in steps to beta* = 2 m in IR1 & 5 to increase luminosity. Similarly, it will also be possible to "unsqueeze" locally beta*. A solution with beta* = 90 m in IR5 for early Totem operation has been studied. The crossing angle would be limited to about +/-60 murad which excludes operation under nominal conditions (2808 bunches, 25ns spacing), but which is compatible with early 43 or 156 bunch operation and beta* = 2 m in IR1. As the 90 m option in IR5 is based on the standard optics, and it only requires the commissioning of the "unsqueeze" but no separate injection and ramp, the time needed for commissioning can be expected to be significantly less than for the high beta option.
  • Totem: The 90 m option has a good physics potential even at moderate luminosity and should allow a first determination of the total cross-section to within 5%. Totem intends to submit a request to the LHCC for the 90 m option for their initial run.
  • Next steps for LOC:
    • Generate an optics for Beam 2 with 90 m beta*.
    • Test of the 90 m optics together with
      • the early commissioning configuration, i.e. beta* equal to 2 m in IP1/5 and 8 and 10 m in IP2
      • nominal configuration, i.e. beta* equal to 0.55 in IP1/5 and 10 m in IP2/8
    • Matching of the intermediate files needed to demonstrate the feasibility of the "unsqueeze" from the injection/ramp to the 90 m optics.
    • Short written statement on the feasibility of the 90 m option an estimate of the time needed for commissioning compared to the high beta options for the next LHCC.

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