Minutes of the 4^th Timing Working Group Meeting (TimWG)
Held on Wednesday the 28^th May 1999

  Present:

Excused:

Agenda

• Approval of previous minutes
• RF SPS timing requirements. Philippe BAUDRENGHIEN
• Slow timing requirements. Adriaan RIJLLART
• Next speakers
• Next meeting
• AOB

Approval of previous minutes
 
Philippe BAUDRENGHIEN reminded that the rephasing in the SPS will be done on the 450 GeV beam and not on the 450 GeV SPS RF frequency as mentioned. He  explained also that the cavity beam loading may not be a problem for the CMS tests as low intensity beams are required.

Michel JONKER required to John PETT real figures of  the magnetic history in LHC impact on the CBCM system. John PETT replied that no figures are actually available but that he is convinced that there will be a strong coupling between both machine during filling period.

RF LHC timing requirements
 
Philippe BAUDRENGHIEN presented a first look of the timing requirements from the RF (see slides attached). He outlined the utility of three different types of timing for the RF:

• CERN wide fine time reference,
• Fine timing,
• Coarse timing.

For the CERN wide reference, he suggested that a common time reference (10 MHz) should be used as time reference for all timings (CPS, SPS, LHC) and as an external reference for all the RF synthesizers used in the various RF groups.

For the fine timing, he explained that a good matching of the SPS-LHC transfers depends on a good measurement of LHC magnetic field,  beam energy and  revolution frequency. He requested different tools to monitor the capture in the LHC in order to be able to measure the closed orbit and the first turn at injection of each batch. He suggested to use the same approach as in the LEP for the distribution of the LHC injection kicker fast prepulses (SPS extraction - LHC injection). He proposed to have, as for LEP,  a veto on the prepulse distribution in case of errors for example bad beam emittance in the SPS, bad synchronization between the machines... He mentioned also that the selection of the LHC beam and LHC bucket during filling must be generated by the LHC control system and received by the LHC RF before CPS-SPS transfer.

Regarding the coarse timing, he explained that during filling the RF processes (capture, damping of transverse and longitudinal oscillations...) are event driven and that during ramping most of the RF parameters depend on the beam momentum. As the SPS and LHC timing are synchronous during filling, he wished to pilot the LHC RF with a sequence of events similar to the one he uses in the SPS. During ramping, he suggested to use momentum driven timing and to encode in tables the RF voltage vs. the beam momentum. He raised up the question of the technical implementation and responsibility of this implementation.

He reminded also that some RF processes will take place during ramping and that they involve the dynamics of the beam so that the freeze of the RF parameters will not freeze the beam parameters. As these processes are are event driven, he suggested to have a mechanism to generated events at a fixed value of the momentum.

During the discussion, the possibility to freeze the ramp at an unpredicted beam momentum  has been raised up by Michel JONKER. It appeared rapidly that it will be difficult for the RF and for the power converter to handle unscheduled stops of the ramp. The major difficulty is to determine how to continue the ramp after an unpredicted freeze mainly due to the influence of its duration on the magnetic field.

LHC equipment group slow timing requirements

Adriaan RIJLAART presented the requirements for the different LHC groups. He explained that typically it is foreseen that each equipment has its own internal clock system and that a re-synchronization will be performed continuously at different time interval with a central reference clock.
 

Next meeting

Next Meeting will be held  on Friday 11 June 1999 at 9:00 AM in 864 1C01.

Agenda

1. Approval of previous minutes
2. Beam Instrumentation: slow and fast  requirements. Jean-Jacques SAVIOZ
3. PS requirements for LHC. Julian LEWIS
4. Next speakers
5. Next meeting
6. AOB