Summary notes of the LCU meeting on 26/02/2008

Present: IA, MA, IB, RB, CB, HB, RDM, UD, SF, MG, AGA, WH, JJ, PL, AM, MM, JN, TP, VP, TR, FR, FS, RT, TW, SW, SY

Report from meetings

• ICC -> MG
  The connection crystostats (corresponding to the missing dipole in the dispersion suppressors) will be opened to reinforce the electrical insulation. A detailed procedure to avoid any problem at the level of the geometry after reparation (and hence mechanical aperture) was defined by JBJ in collaboration with J.-P. Tock and TS/SU experts. For the the case of the first two cryostats, for which the procedure was not available yet, additional measurements were made after the repairing action and the potential aperture loss of 1.4 mm was avoided. 
  Sector 4-5 will be warmed up.
  Sector 5-6 is in cool down to be followed by power tests.
  Alignment surveys after cool down revealed longitudinal displacements and cracks in the concrete were found in the middle of the arc 1-2. A careful verification of the situation elsewhere in the ring is on-going.
  Schedule updates were discussed. The first possible date for beam at top energy is likely to move to August.
• SLM -> MG
  An extended LTC meeting will take place next week at CERN. It will be a sort of Chamonix-like Workshop. The aim is to review the results of the hardware commissioning, beam commissioning plans, and make a readiness review for the systems under AB responsibility. The details of the agenda can be found at the following link http://indico.cern.ch/conferenceOtherViews.py?view=cdsagenda&confId=28066

Overview of current status of LHC Phase I upgrade studies -> MG and SF

MG reports that the LHC upgrade becomes an official CERN project (White paper activity), with Ranko Ostojic (AT) as project leader. Several of us including SF, TR, RdM, RT, MA, WH, and MM are involved in this project, mostly on the level of optics studies. SF prepared a number of work packages aimed at defining the layout of the future insertions, which were assigned to the various contributors. SF comments on the on-going work. The crucial issue is the off-momentum beta-beating, which is considered to be unacceptably large for an optics solution with beta* of 25 cm. A correction scheme was found by SF, which relies on special phase advances in the arcs and insertions. Hence, the current activities are devoted to the insertion and arcs tunability to assess whether the proposed approach to cure the off-momentum beta-beating can be implemented.
MG reports that in view of the new organisation of the insertion upgrade studies the LCU meeting organised every other week will be stopped. The progress of the upgrade studies will be reported either at the regular LCU meeting every other Tuesday or during ad-hoc meetings.

Particle losses at collimators during magnet powering failures: distribution of impact parameter -> Andres Gomez Alonso (pdf)
MG reports that with the help of FS and Eric Mcintosh tracking studies resumed aiming at more realistic simulations of the actual LHC (machine as-built). These simulations will include also studies for Beam 2, which was never considered in numerical simulations in the past. For the computer platform, there was a move from LSF towards BOINC. The change of the platform was very easy and smooth, thanks to the excellent environment developed by Eric and Frank. It appears that BOINC is working very well and it should allow getting massive computing power and good response time.

The change of computer platform was indeed triggered by the heavy use of the ABP-dedicated LSF nodes for machine protection studies made by Andres. This triggered the idea of presenting the outcome of the numerical simulations at the LCU meeting.
Simulations of failure cases is based on tracking with MAD-X, post impact follow up with SIXTRACK, plus FLUKA for simulation of particles in matter. Dipole failures generate clear loss patterns and are easier to simulate than quadrupole failures, which generate a subsequent optics change with emittance blow up possible due to crossing of resonances. About 130 failure cases were considered so far. Some fraction of these were simulated in detail.  Storing and analysing the large amount of simulation results is an issue. Parametrisation of the results with the construction of approximate probability distribution functions turned out to be very useful. Average impact parameters on collimators are normally of the order of 5 micrometer. For dipole failures, much larger impact parameters of the order of 600 mum were found. The failure signatures change substantially from 450 GeV to 7 TeV beam energy. At 450 GeV, showers are wider and the aperture is tighter. It would be interesting to extend the simulations to predict the BLM response.

HB suggests to use the predicted time distributions of losses to identify the origin of the problem and distinguish between beam induced quenches and losses originating in equipment failure.

AOB
None.

Last update: 10-March-08

MG & HB

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