Minutes of the 18^th Timing Working Group Meeting (TimWG)
Held on Friday the 16^th August 2001

Present:

Agenda

• Accuracy requirements of the 40MHz and frev signals for the experiments
• Slow timing transmission and distribution
• Functional specification
• AOB

Approval of previous minutes

There were no corrections on the previous minutes.

Accuracy requirements of the 40MHz and frev signals for the experiments

Emmanuel TSESMELIS explained  that the final requirements on the 40MHz accuracy from experiments  (DAQ & Trigger) will be available end of September. Actually, a very large discrepancy on the jitter acceptable on the 40 MHz exist between experiments (between 150ps and 50ps). He reminded that the 40MHz will be distributed to the experiments through the TTC and explained that the distribution system has to face two different types of jitter: short time and long term jitters. It appears clearly that the long term jitter (phase drift)  will require to be periodically adjusted during a physics run. Some delays (100ps steps) have been foreseen inside the TTC system in order to compensate distribution drift and perform fine adjustments. Emmanuel TSESMELIS confirmed also that experiments don't have specifics requirements on the revolution frequency.

Slow timing transmission and distribution

Gary BEETHAM explained that the distribution of the LHC slow timing will be based on point to point fiber optic links between PCR and the different LHC points. He confirmed also that how the timing will be distributed to the LHC alcoves is not yet fixed.  The MTG, located in the PCR, will be synchronized with UTC in order to avoid time shift between millisecond and time of day. A PLL will be included in the chain in order to keep a very accurate distribution of the 1ms clock. Regarding the question of a possible missing ms clock and the possibility to lock the system on a wrong ms, it appeared that this error has been extremely rare up to now. Nevertheless, as the ms clock will be a fundamental LHC tick, a continuous monitoring of the timing distribution system appears mandatory up to the lowest level of the distribution chain. 

Functional specification

Gary BEETHAM announced that the working group has to provide a functional specification for the  LHC machine timing system. It will contain the slow timing requirements and an amendment for the fast timing will be attached later. Despite the fact that some information have still to be discussed and/or clarified (distribution of machine information inside the event frame, use wild character in the telegram frame...), work will be started on the LHC slow timing distribution specification. The objective is to have a first version of this functional specification end of October. Technical specifications have to be provided at a later stage in order to complete the functional specifications. 

Next meeting

Next meeting will be held Friday 26 October 2001, at 10h00 in 864-1C01

Agenda

1) Comments on previous minutes !!!
2) Functional Specification, All
3) Status of Fast Timing system, Philippe
4) Status of BST/TTC, J-J
5) Interim wind-down