Summary notes of the LCU meeting on 05/11/2007

Present: IA, RA, GB, CB, RB, HB, RC, RDM, UD, MG, WH, JJ, PL, VP, TR, FR, FS, RT, TW, SW

Report from meetings

• SLM -> MG
  MG asks that people who would like to go the EPAC'08 conference sent him an email by Wednesday with a short description of the subjects they would like to present. The aim is to decide about EPAC'08 participation on the group and department level before actual abstract submission to the conference.
• ICC -> MG
  As already reported last time, the leak in sector 4-5 was fixed and cooling resumed. By mistake, oil in a refrigerator was contaminated with water. The tank was meanwhile emptied, dried and cleaned and cool-down continued. The plan is to reach 4.5 Kelvin this week and to continue towards 1.9 K next week.
  Pressure tests in the other sectors continue.
  The TI2 injection tests were successful.
  There will be further follow up the PIMs. As pointed out by EM, their impedance is not easy to calculate and measurements would be very useful. Fritz Caspers plans to perform such measurements.

Chromatic phase space cuts from collimation -> CB (pdf)

CB reported about studies of the off momentum beta-beat in the LHC relevant for collimation performance. The studies were performed with crossing angle on and separation off covering energy offsets of up to ±4×10^-3. By design, the momentum collimators in IR3 are located in places with significant normalized dispersion. Off-momentum particles will be displaced due to the dispersion and be removed some sigma before the on-momentum particles. The tolerances between primary, secondary and tertiary collimator settings are rather tight and as a result of the off-momentum beta beating, off-momentum halo particles may first hit a secondary or tertiary collimator. Alternative settings with larger tolerances between primary, secondary and tertiary collimators were also looked at.

The studies were performed using the optics configurations with phase advances between IP1/5 and IP5/1 such that the beta-beating is minimized either in the first or in the second half of the machine. All the sextupole families are powered to minimize the non-linear chromaticity. The outcome of the studies is that the preferred configuration is the one with the off-momentum beta-beating corrected in the second half of the machine, so that it is minimized in IR7.
Preliminary results for Phase 1 upgrade optics (low betamax) are also presented: as suspected, the situation is more critical as the off-momentum beta-beating is increased with respect to the nominal configuration. The studies are, in any case, on-going.

Status of the LHC optics correction -> RT (pdf)
RT presented the current status of studies concerning optics correction, and in particular beta beating in the LHC. Several alternative methods have been studied and give promising results and could complement each other. The method of response matrix analysis uses a single kick and multi-turn BPM acquisition. Other methods are based on the analysis of closed orbits or phase advance. These methods still work if up to about 10% of the BPMs are not usable. In addition, it is planned to look also at correction based on K-modulation (at least of IR quadrupoles, where such an approach could be easily implemented). HB suggested to measure also locally beta functions in critical places, and in particular the beta* at the IPs. It is also planned to use an AC dipole to excite oscillations for optics measurements. Online optics corrections in the LHC using an application developed by G. Vanbavinckhove (ABP/LCU) is planned.

RHIC experiments as a test bench for the LHC -> Rama Calaga (pdf)
RC continued to report about optics correction, but this time tested on the RHIC machine in 2006 and 2007. The correction algorithms worked well and allowed to localize and correct local gradient errors introduced in the tests. Up to 10% missing BPMs can be tolerated. Good correction require a well corrected chromaticity, with Q' of order 1. It is planned to continue these tests in 2008 and to test the LHC online optics correction application on RHIC.

Using SDDS files in Mathematica -> JJ ( link here)
JJ demonstrated how Mathematica 6 with J/Link to Java can be conveniently used to decode and plot the SDDS files written by various instruments. This is a very nice tool to ease the analysis of MD data.

AOB
Frank Schmidt (pdf) showed that splitting of Mad-X sequences is now possible using a new split command, introduced by Hans Grote. This is important for using PTC for the LHC on-line model as developed during the last visit of Etienne.
Thys Risselada reported about updates to the optics V6.501 based on new data for alignment and magnet aperture provided by MG. See (pdf) for the latest aperture results. The minimum n1 value for Beam 2 in Ir3 is still too low and another iteration seems to be necessary.

Last update: 12-November-07

MG & HB

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