Summary notes of the LCU meeting on 03/09/2013

Present: RB, HB, RDM,LD, OD, MKF, MF, MG, JJ, ALan, ALat, YL, SR, MS, PS, RT, AS, MV

Report from meetings

• SLM and general information -> MG
  Welcome for three new members to strengthen our team:
  Andrea Santamaria who works with Helmut on the HL-LHC, related to the interaction region geometry and aperture including LHCb and with Rogelio on local chromatic corrections.
  Georgi Georgiev who works as technical student with Piotr on PTC in MAD-X.
  Martin Valen, a computer scientist who works with Laurent on the MAD-X scripting language and parser.
  Massimo received information about known non-conformities including aperture reductions by rf-contacts in the LHC. Some of these have been with us already when LHC started first operation and others were found more recently in LS1. Massimo agreed to prepare a summary slide on this which is attached to these minutes here.

• Collimation status -> SR
  A first report on the design of collimators with embedded wire for beam-beam compensation to be used in machine studies is being prepared.
  Details of the TCL layouts around IP1&5 were studied. It appears now reasonable to get the full set of TCL4, 5, 6  collimators around IP1&5 installed in LS1.
  Further work is done in follow up of the recent collimation review.
  A meeting more on the management level on the collaboration between collimation and FLUKA teams is planned to be organised towards the end of this month.
• MAD-X status and further -> LD
  Laurent said that many changes were implemented recently, some of which resulted in failing of tests. These are being analysed and fixed to arrive soon at a consistent production version. One example is C++ compiler portability issues which became apparent by the upgrade of makethin. There is also one example were a bug was found and recently fixed in MAD-X, resulting in failing of tests related to the PS. It turned out, that the MAD-X sequence used in the test actually gave correct results by using a workaround for the bug, which now has to be removed.
  Laurent said that structured lines are not always well supported. John and Helmut reminded that structured lines are important for the design of new machines.
  Ghislain found approximations in the aperture module which only work for the LHC and require fixing. Ghislain continues to work on the online model in close collaboration with operation.
  Laurent proposes to review the choice of the basic canonical variables for the new MAD planned on the longer term. Massimo said that fundamental changes should be coordinated with SIXTRACK and discussed with all people in the LCU (at least).
  Andrea Latina implemented thick quadrupole tracking in MAD-X. Together with the upgrade of makethin, it is now possible to keep selected quadrupoles thick in slicing and perform thick lens MAD-X tracking.
  As a last general point, Laurent remarked that questions for MAD-X should now go to the generic email address mad@cern.ch.

Summary of aperture measurements and comparisons with n1 method -> RB (slides)

Roderick reviewed the tolerances used for aperture estimate using n1  and comparing different sets of parameters against aperture measurements.
Measurements in the real machine have shown that the actual aperture is compatible with a well-aligned machine and much smaller values for the tolerances than what assumed in the design stage. This is the outcome of the sorting performed during installation, the alignment, and optics corrections. These allowed to reduce the beta beating below 10%. The measured aperture can be reproduced by n1 calculations with tighter parameters (bbeat=1.05, cor=0.01, dp=0, see the slides for details). It is clear that in principle a huge number of combinations of parameters used for n1 computation could provide values in agreement with the measured aperture. The correct approach would be to select those values fitting the experimental observation, e.g., of beta-beating, orbit excursion, and momentum offset. 
Massimo proposed to use two sets of parameters, the original set for comparison with the standard LHC design and a tighter set optimized for performance reach.
Helmut reminded that the high luminosity LHC upgrade significantly reduces the passive protection for the experiments (~ doubling the TAS radius, reducing the central beam pipes, higher intensities) and that the aperture specification for the HL-LHC should not be too generous. This, of course, should be carefully studied in a quantitative way.

AOB 

None

Last update: 11-September-2013

MG & HB

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