Summary notes of the LCU meeting on 15/12/2009

Present:  MA, HB, RC, OD, SF, MF, MG, BH, JJ, YL, JN, AR, FS, MS, YS, DW, FZ, LH

Report from meetings

• SLM and general information -> MG
  The LHC startup progress is impressive and also produced already over one million pp collisions recorded by the experiments at injection energy.
  Beta beating was measured at injection and top energy (1.18 TeV). At top energy, the initial beta beating is already within the specified 20 % margin.
  Tests with separation bumps on and beta* knobs were planned for last night, but delayed by vacuum problems.
  It was also proposed to try a first partial squeeze, before beams will be stopped in 1.5 days until mid February.
• CWG -> DW
  AR and DW reported that collimators have been set up for injection and checked with loss maps obtained by measurements with enhanced losses close to tunes of 1/3.
• HB -> LBS
  The 9th LBS meeting discussed first observations and adjustments with beams as well as the status of simulations. A combined LPC+LBS meeting is planned for the 18 January from 14:00 - 18:00 with reports from all experiments and a summary of relevant observations and plans for the machine.
• FZ -> LMC
  FZ reported from the last LMC meetings with particular emphasis on the progress with the beam commissioning. Details can be found in the minutes.

Linear imperfections in new cold D1 dipole for LHC upgrade -> BH (slides)

BH introduced the doctoral student Lutz Hein who works with him on Linac4.

BH described the LHC upgrade studies related to the planned new, large aperture D1 separation dipole. The original field quality was studied by computing the resulting DA of the new layout. Non-linear corrector packages have to be added and the high-order multipoles should be reduced in order to achieve a nominal value for the DA.
Recently, the low-order multipoles were also studied taking into account their impact on beta-beating, tune shift, and coupling. The value of these low-order multipoles is vital for the day-to-day operation, as any change in the crossing angle, or separation bumps will have a direct impact on the beta-beating, tune shift and coupling of the machine. It is clear that tighter bounds should be given to these multipoles in order to reduce their impact on machine operation. This study led to a new revised error table that should be communicated to US colleagues for consideration. It is also worth mentioning that the field quality of the proposed D1 cold magnet is currently much worse that the one of the D1 installed in the LHC in IR2/8 (not to mention the warm D1, which is better for obvious reasons).

LHC optics studies with MAD-X, PTC, and beam measurements -> OD (slides)

OD reported about optics studies with MAD-X, PTC and beam measurements during the LHC commissioning.
The analysis of the off-momentum beta-beating started with a comparison between MAD-X and PTC: some of the differences are due to the different model used for the two codes (in both cases thick lens to enable using the settings directly extracted from the machine).
The dispersion measurements show a beating at the level of 10% in particular in sector 3-4 and 4-5. The beating decreases with energy by about a factor of two. It is planned to use the dispersion measurements to constrain the search for optic errors from the beta-beating measurements.
The quality of the LHC measurements is general very good and allows to cross check BPMs. He showed a list of suspicious BPMs: MG suggest to communicate this to BI (Rhodri Jones) for further action. It is worth mentioning that systematic BPMs check were also performed by OP and the results used to fix a number of monitors during dedicated accesses to the LHC tunnel.

Noise in MADX thin-lens tracking module -> YS (slides)

YS has added features to MAD-X which allow to simulate ripple on magnets, the so-called NOISE element. Amplitude, frequency, and phase can be specified. He showed that this can be used to study emittance growth. MG suggest to use this to study the effect on the noise on the damper recently observed during the beam commissioning.
MAD-X aperture modeling was extended to allow for offsets in the description of the aperture. These offset will be active only in the MAD-X tracking, but not in the aperture computation (for which the only way of defining offset is via a separate offset file). SF suggests to add the option of specifying a tilt in the transverse plane of the aperture (the new implementation foresees only transverse shifts).
YS also presented a number of checks he made on the 6D beam-beam elements. He used such an element when studying the beam-beam effects for a crab cavity in the LHC. The 6D beam-beam element might be useful for the parameter range of the LHC Phase I upgrade scenario. In this context SF asked for clarifications concerning the conventions used for the sign of the crossing angle (should it be that of the strong or of the weak beam). The checks presented do not seem to be conclusive. It is decided that YS will continue the investigations, while in parallel FS clarifies the theory and the implementation in SixTrack.

AOB

None

Last update: 16-December-09

MG & HB

Back to LCU Minutes