Summary notes of the LCU meeting on 24/03/2009

Present: MA, JB, CB, HB, MF, SF, MG, BH, JJ, EL, JM, JN, TR, FR, FS, RT, SW, SY, FZ

Report from meetings

• SLM -> MG
  There has been follow up on LHC alignment. We are asked to specify the requirements: MG will follow this up.
• General information
  There was a discussion in the last LMC on MCBX correctors and the required speed to bring beams into collisions. the decision was taken to perform tests in the second half of May. Specifications about the test condition should be provided (to be followed up by HB et al.).
  FS said there are regular FIDEL meetings which he attends.
  FZ introduced master student Anders Eide who works on the Linac Ring option for the LHeC.

Release of next MAD-X version -> FS (pdf)

FS reported that a new major version 4 of MAD-X will be released very soon. There will be no more individual bv flag in this new MAD-X version, but only the beam bv flag. The default LHC sequence files will be changed at the same time.
The previous MAD-X version 3 will be renamed  to madx_old and remains available for comparison with old files with the individual bv flag. The sequence files will be moved to a special directory /afs/cern.ch/eng/lhc/optics/V6.053/obsolete.

There will be only a single executable of MAD-X  (per platform) which now always includes PTC. The f77 compiler is not supported any more. All Fortran code is converted into Fortran 90. A MAD-X meeting will be organized and give further information on the changes. The meeting is also foreseen to get feedback on features required by the users. Then, it will be evaluated whether these features can be implemented in future releases.

Loss maps of physics debris protons around ATLAS: impact on the LHC and on the proposed physics at 220m -> FeRo (pdf)

FeRo presented his work on simulations, which is done within the ATLAS forward physics collaboration.
Two forward detectors, at 220m and 420m from the IP are foreseen. They would be used both at intermediate and high luminosity operation to tag forward protons from interactions. The next step will be to write a TDR for ATLAS approval.
FeRo uses DPMJET to simulate the collisions and THINTRACK, PTCTRACK and sector maps for tracking. The aim is to assess the impact of the TCL4/5 on the protection of the downstream magnetic elements taking into account also the settings required for the two forward detectors to run effectively.
A previous study concerning the TCL5 was made by I. Baichev and J.-B. Jeanneret (LHC PN 208). Most of the results obtained by FeRo agrees with the previous ones, the main difference being the distribution of debris from the IP.
The new topic under study is the analysis of the combined setting of the two collimators, namely TCL4/5.
In summary it turned out that the TCL4 is effective in protecting not only the Q4, but also the Q5. On the other hand the TCL5 is only partially effective in protecting the DS: in this respect an element next to Q6 (where the dispersion is larger) would be a better solution.
These studies will be presented and discussed at the LBS and collimation working groups.

Update on collimation study with global crab cavity (CC) -> YS (pdf)

YS reported about further work on the compatibility of a global crab cavity (CC) with collimation. He performed simulations with the CC ramped in 1000 turns and finds results rather similar to simulations without CC.
The analysis of the required halo distribution for the CC simulations is presented.
finally, YP showed the phase space cuts for momentum collimation without and with crab cavity. The first case was already worked out by RA and CB from the collimation team for a proposed Phase I upgrade optics. the crab dispersion is computed and taken into account. then, the effective difference in amplitude between the primary and secondary collimators become really small, with the risk that the secondary collimator becomes a primary one. Furthermore, the phase space cuts now feature a sizeable cut in betatron amplitude whenever the momentum offset spans through the allowed range.
SF asked also to repeat the check with the new Phase I upgrade optics where the reduction may be larger.

Dynamic aperture study for LHC -> YS (pdf)

YS also performed studies of the dynamic aperture in the presence of a crab cavity and of the stray field of the CMS solenoid:
Short-term DA computed with MAD-X and SixTrack now agree to within one sigma. The number of angles used to compute DA was increased for SixTrack simulations, but not MAD-X (however, the amplitude scan for MAD-X is now finer, 0.2 sigma).
Difference in DA vs. Dp/p are observed at injection, but not at collision.
Crab cavity studies: global crab cavity does not reduced DA for nominal collision optics (but local crab cavity does). for the Low-betamax optics, both local and global crab cavity reduce DA.
CMS stray field: the weak solenoids at the triplets interconnects generate a short-term DA reduction at injection. It is worth stressing that no coupling correction is performed. Concerning the next steps:
        + implement coupling correction
        + implement solenoid in the MAD-X to SixTrack convertor
        + implement solenoid in SixTrack to perform long-term DA computations

AOB

None

Last update: 30-March-09

MG & HB

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