Summary notes of LCU meeting on 07/05/2007

Present: RA, HB, RDM, UD, SF, MG, AGA, AG, WH, JJ, TK, MM, EM, BS, HM, VP, TR, FS, RT, TW, SW, FZ

Follow up of actions

• History of phase advance of TCLIs in TI2, 8  -> TR
  TR shortly recalled the main role of the TDI and TCLIs, which is to provide passive protection in case of misfiring of the injection kickers. The TDI provides the main protection and is always placed at 90 degrees phase advance from the injection kickers. The TCDIs used to  be placed at +/- 20 degrees with respect to the TDIs and complement the protection in phase space, see the slides. Due to space constraints this became +/- 30 degrees, see the LTC presentation by OB in march 2004. TR found out about 40 degrees for the actual phase advance difference in V6.500 and V6.501. To be discussed in the upcoming injection working group meeting. Requires further follow up.
• SuperB -> JJ
  JJ informed us about the plans for a SuperB (1.e36 luminosity) machine based on a novel crab-waist collision scheme. JJ attended last Friday a meeting in Frascati where the project was presented. The CDR is published. The proposal is to build this machine in Rome within the framework of the CERN strategy. You are all encouraged to look at the CDR and give any feedback to JJ this week. Tests of the new scheme for high luminosity are planned later this year at Daphne.

Report from meetings

• SLM -> MG
  A general group meeting is planned for May-June reviewing the work in the sections. An email was circulated on fellow requests.
  For the upcoming CAS, there are two candidates to participate from our group : Simon White and Valentina Previtali.
• ICC -> MG
  C. Hauviller reported about a review of the triplet problem after an analysis at CERN. Safety margins were underestimated and piping and support will have to be reinforced in addition to the repairing work on the cold-mass supports.
  The cooldown of parts of the LHC continues. Some problems with condensation appeared on the DFBs with consequences for power convertor tests. A new LHC schedule should be ready for presentation in mid-May. It appears already clear now that there will be no engineering run this year. A sector or quadrant test in the LHC is under study.

Progress and plans for the LHC MAD-X on-line model -> FS (pdf file)
FS presented the LHC MAD-X on-line model. It will not control directly the machine, but rather allow to quickly test, simulate and analyse the expected machine response. A typical response time of the model would be about a minute. It is believed that the LHC is rather complex and difficult to operate, such that a detailed modeling is mandatory. Technically, MAD-X can be considered as the standard MAD-X with additional code including the SDDS library to allow for access of machine data and control. An essential part is linear and non-linear magnet modeling with input from Fidel/Wise. Information concerning the machine as built (aperture, misalignment) will be crucial.
The on-line model will be ready to run in the start-up. It is also expected that the on-line model will continue to evolve with the running machine.
RA, SF and HB asked about implementation of correction knobs. There is a general consensus that this part is crucial for the on-line model. Examples of knows will be given and implemented. In addition, discussions will be launched in order to assess the possibility of implementing knobs in the control system with input from the on-line model.

LHC impedance status and strategy -> EM (pdf file)
EM presented the ongoing work and plans on the LHC impedance. He introduced two students: Hubert Medina who works with us for five month with an implementation of the Mathematica-based code REWALL (for the computation of the resistive wall impedance) in ZBASE. Benoit Salvant who works on a PhD thesis with and upgrade of REWALL and extension on longitudinal impedance. With these contributions, ZBASE should allow generating the impedance of the various LHC components, sum them up, and generate the corresponding wake-field for use in external codes (HEAD-TAIL or MTRISIM).
As far as the impedance budget is concerned, the details (properties of the mu-metal for the chambers in the septa) are needed to complete the evaluation of the impact of the septa on the overall LHC impedance. 
EM showed the stability diagrams for the nominal LHC beams at injection, before the squeeze and in physics. The LHC impedance is largely dominated by the collimators. According to current estimates, the nominal LHC would be outside the stability region provided by octupoles with collimators in physics settings. The transverse feedback can be used to stabilise beams, but would also increase the emittance.
RA and SF asked about the effect of chromaticity, Q'' and stability without  octupoles. HB asked about related plans for commissioning. It is clear that this subject should be covered in the future (end of the year) with the help of a PhD student or a fellow. In this respect it will be crucial to support the code MTRISIM (by AK) and, if needed, to upgrade it in order to implement the required physics.
It is also clear that the experimental verification of the inductive by-pass effect is crucial. A strategy to achieve this result will be prepared and presented in a next meeting.

In order to not finish the meeting too late, it was decided to move the planned presentation
Beam-beam studies and phase advance between IP1/5 -> UD
to the next meeting.

AOB

None

Last update: 7-May-07

MG & HB

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