Summary notes of the LCU meeting on 06/05/2008

Present: IA, MA, CB, RB, HB, RB, RC, MG, JJ, PL, MM, AM, TP, TR, FR, FS, TW, SW, SY, FZ

Report from meetings

• ICC -> MG
  News were rather encouraging. Main dipoles in sector 5-6 reached 5 TeV including a safety margin for reliable operation.
  Triplet magnets were powered to 7 TeV. Systematic polarity problems were found on the triplets. This is followed up with other non-conformities.
  Three sectors are at 1.9 K. Cool down times decreased to 6 weeks.
• SLM -> MG
  There was no meeting last week.

Non-conformities and their consequences ->  MG (pdf)

MG showed and discussed the slides he prepared for the LHCCWG this afternoon. He prepared detailed lists for sectors 5-6 and 4-5. In 5-6 most non-conformities were classified as closed. It is highlighted that the system allows closing a non-conformity with disposition "decision pending"!
Eight of these have decision pending and only one is due to powering. The list for 4-5 is longer, with 19 non-conformities with decision pending. The systematic polarity problems on the triplet were observed in both sectors.

As reported in the LTC on the 30/01/2008, there was an issue with a horizontal closed orbit correct in Q5.R4.B1. The repairing was done in situ. Dedicated tests will be needed to assess whether the repairing action was indeed successful.
A remaining issue is on the choice of the time-dependent parameters, such as dI/dt and d²I/dt², used for the hardware commissioning. In fact, is seems that these values were defined without a detailed analysis of the operational needs. MG will follow this up with the people involved in the hardware commissioning.

New cross section estimates for ion collimation  -> RB (pdf)

RB reported about ion collimation issues with a comparison of predictions obtained using different programs. Nuclear interaction lengths for ions are much shorter than for protons -  38.1 cm for protons in graphite compared to only 2.2 cm for Pb ions. Multiple scattering instead is very similar for protons and ions. This reduces the effectiveness of secondary collimators for ions, since many of the ions will have undergone nuclear interactions before they are scattered into secondary collimators.
A particular issue for heavy ion collimation is due to the production of ions with different Z/A. These ions will be lost in the dispersion suppressors, due to their large momentum deviation. Hence, they will not be intercepted by the secondary collimators.
Numerical simulations performed with ICOSIM predict several spots above quench limits for nominal ion beams. It is worth stressing that the quench limit is affected by a non-negligible uncertainty.

An efficient way to generate the fragmentation cross-sections is required for simulations of collimation performance during the ramp as well as to study improvements, such as new materials for spoilers.

A fixed target experiment is set up with both FLUKA and MARS. The total and partial cross sections are determined by counting the fragments and compared. Predictions from heavy ion collisions differ by factors of up to 2 - 3 in cross sections. Older ABR.ABL based estimates tend to be most pessimistic while MARS give the most optimistic results with FLUKA somewhere in the middle. From now on, FLUKA will be used to generate the cross-sections for the numerical simulations. The uncertainty on the cross-section will be reported on the loss maps as errors bars.

Beta* tuning knobs -> AM (pdf)

Akio Morita  reported abort studies on beta* tuning knobs for the LHC using the SAD/Tkinter codes. The LHC MADX files are translated to SAD convention using SADScript. He trims Q4-Q11 and constraints alpha, beta at the IP and Twiss parameters on both ends of the IR to match the standard LHC optics in the arcs, as well as the closure of the crossing and separation bumps. The vertical dispersion instead is currently not restricted and tends to go out of control.

For the moment, this work is done as a study with possible application to the online model to allow for small, order of 10 per cent, beta* adjustments in the control room. given the encouraging results, the hardware limits will have to be included and a MADX version should be provided to enable include this algorithm in the on-line model.

AOB
MG reminds that he circulated an email on the TI2/TI8 commissioning. He encourages ABP-LCU contributions and in particular the use of the MADX online model.

Last update: 06-May-08

MG & HB

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