Summary notes of the LCU meeting on 23/09/2008

Present: IA, MA, RB, HB, RC, MF, SF, MG, NH, JJ, YL, AM, JN, FR, FS, RT, TW, SY, JM, SP

Report from meetings

• SLM and general information -> MG
  New members : MG welcomed John Miles who many of us remember well from SPS, LEP and SL/AP times. HB introduced Yngve Levinsen who started this month as CERN doctoral student in our group for a thesis on a "Study of LHC Experimental Conditions and Beam Induced Detector Backgrounds".  Vadim Talanov from IHEP is here for four weeks to help and give advice and LHC background simulations. Miriam Fitterer from Karlsruhe university will work with us until the end of this year on generic halo and tail simulations with applications to the CLIC drive beam.
  The DG designated has presented the management structure effective from 2009. Steve Myers will become director for accelerators and technology. Paul Collier will head the beams department. Changes on the group level are under discussion and will be presented in a general ABP group meeting, in the second half of November. Please see directly Massimo or Oliver for questions, suggestions, or to expression opinions and views on this subject.
  After a quick LHC start with beams on the 10 September, and a few days stop with transformer changes, Beam 1 was back in the LHC during the night from Thursday to Friday. Friday at 11:17 sector 3-4 dropped during the last commissioning step of the main dipole circuit to the 5.5 TeV level. See the Press release for details. An update will be given in the 8:30 meeting on Friday.

MG reviews briefly the on-going activities:
•  
Polarity checks: understanding of the polarity conventions and debugging of the polarity flag in the MAD-X sequence (in collaboration with S. Russenschuck). Analysis of the beam measurements concerning polarities of LHC circuits are also in progress.
• Optics: new optics with optimized phase advance between IP1/5. Aperture checks are in progress and will be reported at the next meeting.
• Aperture: the new file with vacuum markers is being cross-checked.
• Parallel separation: a study to define a parallel separation scheme aimed at minimizing the time to collapse it should be performed, as well as simulation of the impact of many small-amplitude long-range beam-beam collisions due to the collapse of the parallel separation scheme.
  

Beam 2 vs. Beam 4 verifications -> FS (pdf)

FS reported about recent MAD-X issues and improvements. Automatic checks performed by J-L.N revealed several issues, mostly in the PTC part which are being fixed. A PTC standalone module for the LHC is in preparation.
He also reported about more recent discussions and checks on sign changes and conventions in the context of the reversed sequence of beam 2 which is also known as beam 4.

The conclusions on this topics will be reported at the next meeting.

Thick lens model with errors and MAD-X status -> FeRo (pdf)
FeRo described his recent work in the context of MAD-X on-line model and PTC.
The idea is to include field errors with PTC to a thick lens model of the LHC. Errors can be read from error tables of measured errors (extracted by WISE and also used for tracking simulations).
The complex chain of scripts was tested using b2 errors in the dipoles. The resulting beta-beating looks in agreement with estimates.
The next step will be to include also the higher-order magnetic errors.
This model, together with the extraction of the actual machine setting (under development by IA and FeRo) should be the basis of the refined on-line model.
In the next meeting the comparison between MADX and PTC (for nominal optics without errors) will be quickly presented as a follow-up.

Emittance growth from crab cavity -> AM (pdf)
AM reported about his studies in the context of the LHC upgrade with crab cavities. He studied how fast the crab cavities should be ramped so to produce a minimum transverse emittance growth. He found that the emittance growth is only substantial if the cavities would be turned on in less than 10 turns. The emittance growth for turn on over 1000 turns is negligible. He used 6D simulations based on the SAD program for 10000 particles and a crab RF-frequency of 400 MHz. The only sources of non-linear effects are the chromatic sextupoles.
In a next presentation the more realistic case with all non-linear magnetic errors should be presented together with a study of the 800 MHz case.

AOB

None

Last update: 23-September-08

MG & HB

Back to LCU Minutes