Minutes of the LCU Section meeting

Summary notes of the LCU meeting on 11/03/2008

Present: IA, MA, CB, HB, MG, WH, JJ, PL, AM, MM, JN, TP, TR, FR, FS,TW, SW, SY

Report from meetings

eLTC -> MG
The extended LTC meeting took place last week. A summary will be given on Friday 14 March.
To speed up getting collisions this year the beam energy may be reduced to 5 TeV as this would avoid training quenches. Such quenches require still a substantial recovery time as cryogenics is still to be mastered perfectly.
The possibility of injecting first into a part of the LHC in a sort of sector (or quadrant) test was reconsidered. Commissioning of the whole ring appears to be the preferred option with a sector test as backup in case of delays with part of the LHC.
SLM -> MG
There was no meeting due to the eLTC.

Do we have to ramp the LHCb spectrometer magnet ? -> WH, MM (pdf)

This question came up recently in the LHCCWG, but was in fact already considered as long as 12 years ago and reconsidered in the 2006 Chamonix workshop, where WH already made a presentation on this topic. It is in principle relevant for both ALICE and LHCb. The discussion here focused on LHCb, where the situation is more difficult with internal and external crossing angles being both in the same (horizontal) plane.
For operation we would normally ramp with constant deflection, implying that we would reduce the spectrometer excitation at injection to 450GeV/7TeV = 6.4 %. The experiments would prefer constant field to avoid stresses during the ramp, which might damage the coils insulation.

For early operation without external crossing angle there is enough aperture to keep the spectrometer at full current. With crossing angle, however, this is only possible for one spectrometer polarity. For the other polarity ramping down to about 7.5 % would be required, which is very similar to what would be required for ramping at constant deflection.

HB said that even if the aperture is sufficient he was worried about the large size (about +/- 10 mm) of the bumps at injection when the spectrometers would be kept at full field, for example in case of failures. Indeed, the worry here is more on the machine protection side, but in principle, the spectrometer compensator magnets should be interlocked and monitored by the FMCM system.

TR asked if there were plans to shift transversally the IR2/8 interaction points to gain in aperture at injection with crossing angle on. WH replied that this was not the case as for this particular study the overall aperture situation cannot be improved by displacing transversally the interaction point.

Anticipating on potential requests from the LHCCWG, WH already considered whether a reduced beam energy is compatible with the aperture requirements and the full strength of the spectrometer. In case of missing external crossing angle any energy is acceptable. In case an external crossing angle is present, the spectrometer magnet can be kept at full field with both polarities as long as the beam energy is higher than 4 TeV and beta* is 10 m.

AOB
John follows up on the interference between the tertiary collimators around ALICE and the spectator neutrons from ion collisions. Ralph is also contributing to the discussion. The actual situation will be reviewed in one of the next meetings.

Last update: 13-March-08

MG & HB

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