Summary notes of the LCU meeting on 23/03/2010

Present: CA, OB, HB, RC, OD, MF, MG, YL, JN, TR, FS, MS, RT, SW, FZ

Report from meetings

• General information -> MG
  P. Charrue presented the French VIA program in a recent management board meeting, which would allow for an increased number of technical students. Similar programs are available for Spain and Portugal.
  MG reminds about an increasing number of thefts in the ABP office area: Delphine already circulated a mail to inform ABP members and suggest measures.
  There is good progress in the LHC re-commissioning. The beta-beating was measured at 3.5 TeV and found to be within the specified tolerances (20%) without extra corrections.
  The coupling corrections were reviewed and improved. For Beam1 no correction is applied. For Beam 2 the previous correction required a huge strength to the MQS, which was exceeding the maximum already at 3.5 TeV. Rogelio et al. measured the coupling and generated a new knob for injection. The strength of the MQS was reduced by a factor between 5 to 10. A different knob was computed for 3.5 TeV and the C- reduced to about 8E-3.
• FZ -> LMC
  FZ reported from the last LMC meetings. Details can be found in the minutes.
• LBS -> HB
  There has been a forum on interfacing to the LHC logging database for data analysis organized by M. Ferro-Luzzi.  People interested in follow up can sign-up for the e-group called acc-logging-data-extraction. The LBS meeting yesterday had presentations from LHCb and CMS on the observation of backgrounds. YL reported on simulation of IP cross talk.

Proposal of new optics for IR3/7 -> TR (slides)

TR reported about his recent work on "Optical corrections in the central regions of the LHC cleaning sections" to make Beam 1 to look again like Beam 2 in the cleaning insertions.

The cleaning insertions were generally optimized in 2003/2004, leaving however some details unfinished, like the dispersion optimization for Beam 1. This was now corrected, resulting in small improvements in terms of normalised dispersion in IR3. TR check that the aperture is ok and proposes to apply these changes soon to the real machine.
In addition, TR considered the issue of improving the situation of the trim quadrupoles (MQWBs) in IR7. Two options were analysed, namely RQT5 set to zero and RQT4 kept to the current strength or RQT5 set to zero and RQT4 increased to about 3% of the nominal strength.
While the first solution gives a negligible variation of optical parameters at the collimators and an unchanged aperture, the second solution features some reduction in aperture. As the magnet experts consider the current level of excitation of the RQT4 in IR7 good enough for the accuracy of the magnet model, this solution is retained.
Following a cross-check to be performed by the Collimation team, one could envisage testing in the machine this optics. Of course, the RQT5 should be pre-cycled with a de-Gaussing cycle in order to have exactly zero field. This is in principle available and could be set-up very quickly.

TOTEM un-squeeze to 90 m -> HB (slides)

HB reported about the matching of the un-squeeze for IR5 from 11m to 90m for the nominal LHC machine. This would allow to test the feasibility of this optics in machine studies this year. He reminded about the particular difficulties of these optics, like phase constraints by roman pots, strength ratio constraints and the need for external tune compensation. Some of this was discussed in earlier LCU meetings (LCU 21/04/2009, 16/06/2009).
Last year it was decided (LMC 14/10/2009), to introduce cables in IP5 to avoid the Beam1 / Beam 2 current ratio constraint. This can only be done in the next longer shutdown. Still, now it should be feasible to get to 90m by using a nearly antisymmetric  Beam 1  / Beam 2 left/right optics to fulfill the strength ratio constraints.
The tuning of the un-squeeze was first done for Beam 1, and resulted in a rather smooth un-squeeze with beta-beating between interpolation points below 1%. The un-squeeze for Beam 2 looks also feasible, but requires further tuning, to be followed by a full check of all convertor limits and aperture constraints.
A study of the proposed solutions including the selected scenario for the tune compensation should be finalized soon.

Analysis of recent aperture measurements in the LHC -> CA (slides)

CA reported about aperture measurements performed this month in the LHC.
The measurements involved the generation of orbit oscillations with +/- sign in both transverse planes, up to the observation of beam losses. The observation agree rather well with the expectations. The agreement is best for Beam 2 in the vertical plane. It is planned to also perform in future measurements off-momentum, and to repeat some measurements which were in doubt due to BLM noise. A detailed analysis of the measurements, including the computation of n1, is expected by Easter.

AOB

None

Last update: 26-March-10

MG & HB

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