Minutes of the LCU Section meeting

Summary notes of the LCU meeting on 24/02/2009

Present: MA, GB, CB, HB, MG, WH, JJ, EL, MF, YL, JM, AR, FS, RT, GV, TW, SW, SY

Report from meetings

SLM -> MG
Access to the tunnel and equipment requires participation in safety courses. An email will be circulated on this subject, in particular concerning the "habilitation électrique" safety course.
Management and committees: two committees, the LHC Machine Committee (LMC) and an injector performance committee have been set up within the new management structure. Both are executive meetings, with attendance mostly restricted to group leaders. In addition to committees, there will be a number of working groups. The last LMC had discussions on cryogenics and the issue of running accelerators through the winter 2009-2010. There will be efforts to minimize the power consumption which require input from us on the heat load by the beam via electron cloud, beam losses and inefficiency of the collimator system.

Impact of possible IR7 optics changes on collimation performance -> JJ (pdf)

JJ looked into optics solutions for ion collimation. As discussed in previous meetings, cryogenic collimators in IR7 are the best solution for ion collimation (as it is the case for protons).
The point of this study is to quantify what could be gained in terms of collimations efficiency by changing the optics of IR7. JJ showed that only a very limited impact on the efficiency could be achieved. Upon request of MG to quantify this effect, JJ added the information in the latest version of the slides: the maximum for the matrix element R16 at the location of the secondary collimators is 0.3 m (this is an extreme case, dramatically violating many conditions on optics and aperture) .

Emittance growth study with MADX -> YS (pdf)

YS reported about the status of his studies on potential emittance growth introduced by turning on of a crab cavity.

Other sources of non-linearities have been included, such as Landau octupoles and multipolar errors in main dipoles and quadrupoles. No significant emittance growth is seen in the simulation whenever the ramp up is slower than few turns. Different ramping times were simulated, as well as different configurations providing non-linear behaviour (Landau octupoles alone, beam-beam alone, non-linear magnetic errors alone). Very short ramping times below 10 turns should better be avoided - which is probably anyway the case due to hardware constraints. These results confirm the previous ones obtained by Akio Morita.
More work is required to assure the compatibility of crab cavity operation with collimation.

Status report on beam gas simulations with SixTrack -> YL (pdf)

YL reported on the implementation of beam-gas scattering for the LHC with tracking by SixTrack, as first part of his PhD work on beam-induced backgrounds in the LHC. He uses a modular approach. DPMJET has been used so far as generator for the beam gas interaction. Vacuum distributions for the LHC are used as input to calculate the scattering probability around the ring. The probability for individual beam particles to undergo beam-gas scattering are very small. For efficient beam-gas simulation, every particle is scattered once in the first passage. SixTrack together with the detailed aperture model from the collimation team is used to track the secondary protons.

Secondary particles other than protons, as well as protons which lost several per cent of their energy will be lost locally. YL proposes an output format. The generated output distributions can be used as input for background simulations of the LHC experiments.

MA asked if there are analytic expressions to predict the emittance growth from beam-gas. This point could be checked and discussed in order to cross check the results.

JJ enquired about the possibility to use the same tools also for gas-ions interaction. In this case the issue is the capability of SixTrack of simulating various ion species (ICOM was developed exactly to solve this aspect). MG asked if SixTrack is sufficiently precise to simulate off momentum particles. FS replied that SixTrack is rather precise to several per cent energy offsets and therefore well adapted for this study. In any case, a verification (by comparing PTC with SixTrack) of the maximum value of Dp/p to be correctly simulated should be performed.

LHC Background Study Group -> HB (pdf)

HB showed the mandate and status of the LHC background study group, chaired by him with Daniela Macina as deputy and Alick Macpherson as scientific secretary. The core team and representatives from the LHC experiments have been defined. Participation is open and all information will be made available on the web. The first meeting is scheduled for the 5/3/2009 at 16:00 in 874-1-11 (at the CCC).

MG asked HB to keep us informed about the work in this meeting.

Twiss module and chromaticity -> FS (pdf)

MAD-X is much used not only for the LHC, but also for CLIC and a number of issues were identified. In addition to the well-know deficiencies in terms of chromatic effects, it was recently found that the chromaticity in presence of coupling is wrongly computed by TWISS. To fix this, as it is not possible to introduce linear coupling in the formalism implemented in TWISS, it was implemented a numerical computation based on two runs of TWISS with Dp/p zero and different from zero. At this point, the TWISS module should be frozen.

It is worth stressing that PTC_TWISS is also available and bug free, i.e., the physics implemented is the correct one, however it is slower with respect to the TWISS module of MAD-X.

Updates are directly made on the MAD-X development version.
A new major new production version MAD-X 4.00.XX is currently being finalized and tested. This requires the help and support of the MAD-X module keepers to correct the examples and update them.

AOB

None

Last update: 26-February-09

MG & HB

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