Summary notes of LCU meeting on 23/04/2007

Present: IA, GB, HB, RDM, UD, SF, MG, AGA, WH, JJ, MM, TP, VP, FR, FS, RT, TW, SW, FZ

Follow up of actions

• Follow up of Injection & V6.501 -> HB
  For the upcoming TI 8 injection test, the optics will have to be frozen soon and it was decided to stay here with V6.500. Otherwise, it is planned to go to optics version V6.501, to be decided in the next InjWG meeting, based on a detailed check list, see the slides. 
  The issue of the phase advance for the TCLIs will be presented by TR in the next LCU meeting.
• Polarities for LHC MAD-X sequences -> MG
  Making sure that the polarities of the magnets in a machine of the size and complexity of the LHC are all correct is a challenge. Proposals have been made to define the magnet polarities exclusively in sequence files, which would have implied major changes to our work with strength files. As proposed by SF, it has now been decided to add the polarity information using a new polarity attribute on the level of the mad sequence files, keeping the previous sign assignments in the strength files such that this upgrade would be fully transparent for our work, see the slides. This implies the definition of a new property of the magnets called "polarity". The layout database was already upgraded to generate a sequence according to this new specification and TR verified that everything is correct. The modification of MADX will be carried out by FS. TR will send the proposal to S. Russenschuck for information and final endorsement.
  MG also informed us about discussions on the issue of lower limits in quadrupole magnet strength. While polarity changes and zero strength are possible for the trim quadrupoles, the other quadrupoles can generally only be regulated down to about 2 - 3 % of the maximum strength. However, it was found that a hard limit is set to 150 A, so that lower values of currents cannot be loaded in the power converter. Unfortunately, for some magnets 150 A corresponds to 4% of the nominal, thus creating a potential conflict with the requirements assumed for injection optics. Follow up is required (Action: MG).
  At the same meeting the reference frame to be used for the magnetic measurements was discussed and agreed upon. In particular it was agreed that:
  • Rotations of single magnets around the s-axis (e.g., for the Q3) will be incorporated directly in the measured multipoles.
  • The magnetic multipoles will be always referred to the connection side of the single magnet.
  • The data concerning the orientation of each magnet in the tunnel as well as the orientation of the cryostat in the tunnel will be extracted from the layout database.

Report from meetings

• LHCCWG and LTC -> FZ
  FZ  reported from the last meetings of the LHCCWG and LTC. The main point in the LHCCWG on April 10 was beam excitation using the aperture kicker or AC dipole for measurements. Commissioning of the vacuum system was also discussed and requires further follow up with the people from the vacuum group.
  The last LTC meeting had a report from the ICC and a presentation by FZ on detailed optics measurements in commissioning. Steve Myers suggested to look into alternative methods to measure beta functions in addition to the planned measurements using multi-turn BPM acquisition. An alternative would be optics measurements based on quadrupole strength or "k" modulation. This requires further follow up : which magnets can be modulated (to be checked with F. Bordry et al.) and concerning the calibration of the amount of the modulation.
• SLM -> MG
  The next student committee meeting will be tomorrow. ABP-LCU has two requests, one for a student to work with RT on optics measurements and beta-beating correction and another to work with HB on the absolute LHC machine luminosity determination. Our candidate for the latter, Simon White is already with us for his three month internship, working with HB on the Atlas high beta optics. Another student arrived to work on his internship with EM on the implementation of an impedance model of the LHC ring and its injectors using Zbase.
• ICC -> MG
  A main issue and concern has been the failure in the triplet of IR5 in the pressure test. It will require a major repair, which cannot be done in situ. Modifications will also be needed in all other triplets. There will be implications on the schedule and decisions are expected by mid May. Discussions to perform a sector or quadrant (dumping the beam in the dump channel) test injecting in IR8 are on-going.
  Cooling tests in LHC sector 78 are in progress and have reached 1.9K, as can be seen from the main LHC page.

Overview of LHC IR upgrade studies -> MG (pdf file)

• A review of the activity and plans for the upgrade studies are presented. In particular, since March, the path to IR upgrade is now split in two stages:
  • Phase 1: it aims at consolidation, increase of flexibility and increase of luminosity by up to a factor 3. It is based on available technology, i.e. NbTi magnets.
  • Phase 2: it aim at an ambitious increase of luminosity by up to a factor of 10 (this requires at the same time an upgrade of the detectors). It is based on new technology, i.e. Nb₃Sn magnets.
• Goal of the studies: prepare an assessment of the three optics solutions prepared by RdM and OB (to be published in a paper with also R. Ostojic as co-author). the deadline is not defined, yet, but it seems judicious to be ready for editing a paper by September this year.
• Working style:
  • Responsible people for optics were defined. Furthermore, people responsible for the various aspects (DA, beam-beam, collimation) were also selected.
  • Dedicated meetings will be organized every other week (Wednesday morning at 10:00), alternating with the general LCU meetings. The first meeting is organized on May 2nd.
  • Optics #3 is the most advanced: all the details are available (Beam 1/2, crossing scheme) to start investigations on DA, beam-beam and collimation.

AOB

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