Summary notes of the LCU meeting on 21/04/2009

Present: MA, CB, HB, SF, MG, WH, BH, JJ, EL, YL, JM, JN, FR, AR, FS, YS, RT, GV, SW, DW

Report from meetings

• SLM -> MG
  MG reminds about the Friday deadline to send PAC papers to him and Oliver as already communicated by email.
  He asked for feedback on how to improve communication in the group between sections for example by common meetings and presentations.
  He reported about further follow up on vacuum chamber alignment in the LHC. The bias in the vertical plane has disappeared (wrong data analysis). Re-alignment has started of LSS4 started assuming a threshold for re-alignment of 4 mm. We would have liked to have this decreased to 3 mm. In any case the re-alignment should be re-done due to the error in the initial data analysis.
• LMC: Q4 powering for high b* operation -> HB and SW (pdf)
  HB reported from the last LMC meeting which had a presentation by David Nisbet on powering requirements for the TOTEM optics. The optics requirements for this LMC preparation were from HB and SW. There will also be a PAC'09 contribution on the TOTEM optics. The LMC took note of the fact that the 0.5 < beam1/beam2 < 2 constraint, which was introduced after the LHC optics design stage, has invalidated the previously agreed TOTEM optics and will require hardware modification before operation will be possible at very high beta* for TOTEM.
  There are two possible scenarios. One would be to swap the Q4 polarity for the high beta* runs for TOTEM as foreseen for the ATLAS high beta operation.
  The other would be to add few cables between the power convertors and the DFBs to eliminate the factor 2 constraint in the beam1/2 ratio.
  The hardware modifications would not necessarily have to be implemented before the first LHC operation. For the first year of LHC operation, TOTEM requested operation at 90m beta* for which optics solutions exist with the LHC as presently installed. HB said that extra cables would allow for more flexibility and that more on the needs will be known after initial LHC operation.

How (and why) we use MCBX for crossing angles and separation bumps -> WH (pdf)

WH recalled the design criteria and the history of the IR layout and correction schemes. The bumps involve the MCBC and MCBY correctors close to Q4 and the special nested MCBX in the triplet. Depending on the energy, the MCBX are needed to get the required strength (important for the crossing angle at top energy and low beta*) or gain in aperture (most relevant at injection). At top energy, the separation bump does not need the MCBX. The crucial point is to avoid transferring the whole strength to the MCBC and MCBY as these might become the bottleneck for the collapsing speed (as showed by SW).
WH recommends to control and adjust collisions with the MCBC and MCBY alone as these provide separate control of the two beams.

Foreseen ramping test of the separation correctors -> SW (pdf)

SW showed the slides he prepared for Mike's commissioning meeting this afternoon and asked for feedback. He proposes a broad spectrum of tests for involving the MCBC, MCBY and MCBX magnets. One objective is to determine in practice how much time is needed to collapse the separation bumps and to adjust the separation. Another aim is to study and optimize the flexibility and to always measure and if possible adjust time scales.
In the following discussion, MG suggested to include bump generation with the online model in these tests.

WH reminded that beams could also be brought into collision longitudinally using the rf. However, the time and the rf power required are not known.

AOB

JJ said he finds we get far too much email within CERN on subjects not really relevant for us or which are better communicated by other means like announcements for special seminars which can be found in the Bulletin and on the web. MG will report this to Oliver.

Last update: 23-April-09

MG & HB

Back to LCU Minutes