Minutes of the 3^th Timing Working Group Meeting (TimWG)
Held on Wednesday the 12^th May 1999

  Present:

Excused:

Julian LEWIS.

Agenda

• Approval of previous minutes
• CMS test beam timing requirements. Emmanuel Tsesmelis
• SPS Master Timing Generator requirements. Michel Jonker
• Next speakers
• Next meeting
• AOB

Approval of previous minutes
 
There was no comments on the previous minutes.

CMS test beam timing requirements
 
Emmanuel TSESMELIS presented the CMS timing requirements for detector equipment validation tests in the SPS north and west area (See slides attached). The two major requirements are:

• Availability of the 25 ns RF beam structure (40.079 MHz) and SPS revolution frequency in the north and west area CMS rooms,
• Request for a single mode optical connection in order to reduce jitter.

Philippe BAUDRENGHIEN  specified that that SPS/RF will try to make the rephasing of the 450 GeV SPS RF frequency to the LHC injection RF frequency. In this case, a fixed frequency will be distributed to CMS. If this is not possible, a model of the RF frequency evolution will be provided to CMS in order to be able to compensate the RF variation. An answer will be given by SL/RF in september.

Jean-Jacques SAVIOZ confirmed that the 300 ps jitter on the fiber optic transmission is due the transmitter/receiver characterisitics plus there is a to a temperature effect which has a random distribution. He confirmed also that the optical source is a laser.

Philippe BAUDRENGHIEN explained that the bunch spacing in the batch depends on the cavity beam loading. A feed back & feed forward regulation system is actually developed in order to compensate this effect. It will be available end of this years. As this phenomena is deterministic and depends on the cavity voltage and beam intensity,  it is possible to avoid this effect by looking always at the same bunch (i.e. synchronization with the SPS revolution frequency).

Philippe BAUDRENGHIEN confirmed that the generation of the LHC revolution frequency (11.246 kHz) is possible inside the SPS-RF faraday cage. Nevertheless, the optical distribution to CMS rooms in the north and west area must be implemented. Gary BEETHAM showed the optical fibers installed around CERN. Optical connections to the North and West area already exist, but an extension to the final location must be foreseen.

SPS Master Timing Generator requirements

Michel JONKER presented a complete overview of the timing distribution mechanisms for the SPS and  LEP, compared the two different solutions and raised up the missing functionalities in the LEP timing (See slides attached). He outlined the basic requirements/functionalities needed for the LHC slow timing:

• Provide a mechanism to apply synchronized commits to parameter modification requests (this mechanism should be available for all equipment: power converters, RF, feedback controls, measurement, injection kickers, SPS, PS, etc...),
• Provide mechanisms for synchronized and sequenced measurement and control procedures,
• Provide a central hart beat for equipment synchronization (e.g. 1-ms clock),
• Distribute calendar events,
• Handle emergency dump requests,
• Distribute machine state (exists in LEP but not used).
• As, the cycling related requirements of LHC will be very minor:
• Filling can be easily implemented with the LHC local timing as being driven from the SPS/PS complex.
• If needed, it could be driven directly by the SPS local timing,
•  Implementation of a simple rendez-vous mechanism:
• The LHC request beam, and then waits for n pilot-pulses and m filling-pulses from the SPS. When it requests, there need to be some kind of guaranteed response from PS/SPS,
• Not only is the LHC machine loosely coupled to the PS/SPS, also the LHC local timing system should be loosely coupled to the PS/SPS complex. Local synchronization and coordination aspects of LHC equipment are much more important.

During his presentation, Michel JONKER observed that a common approach, as for example the solution presented by SL/PC, should be used for all the equipment using slow timing events in order to uniform and simplify synchronization mechanisms. Philippe BAUDRENGHIEN expressed that this kind of approach is not compatible with the RF specific requirements. John PETT reminded that the mandate of the working group is to identify the different LHC timing requirements and, actually, not to find or impose technical solutions.

John PETT reminded the possible influence of the magnetic history in the LHC (i.e. impact of the injection phase duration on the ramp) on the timing distribution and on the beam scheduling inside the CBCM (Central Beam and Cycle Management).

Next meeting

Next Meeting will be held  on Friday 28 May 1999 at 10:00 AM in 864 1C01.
 
Agenda

1. Approval of previous minutes
2. RF SPS timing requirements. Philippe BAUDRENGHIEN
3. Slow timing requirements. Adriaan RIJLLART
4. Next speakers
5. Next meeting
6. AOB