Minutes of the 13^th Timing Working Group Meeting (TimWG)
Held on Friday the 1^th September 2000

Present:

Excused:

Julian LEWIS.

Agenda

• Approval of previous minutes
• BI progress with TTC, Jean-Jacques SAVIOZ
• 10MHz distribution, Gary BEETHAM
• LHC slow timing possibilities, Michel JONKER
• AOB

Approval of previous minutes

There were no corrections on the previous minutes.

BI progress with TTC

Jean-Jacques SAVIOZ reviewed the SL/BI progress made during the last months on the LHC Beam Synchronous Timing (BST) system. He outlined the difference of requirements between LEP and LHC (number of bunches, minimum bunch spacing, minimum overall jitter, number of acquisition crate and crate location) and presented briefly the possible solutions studied (see slides attached).

After an in-depth analysis of the different possibilities, the solution based on a standard LEP BST master and a complete TTC system for the distribution with fiber optic transmission in the tunnel has been selected. This solution requires only specific development at the lower level of the transmission chain (TTC Interface Module). A feasibility study has been performed and different tests realized successfully during the SPS operation period with an LHC structured beam. This solution permits to distribute synchronously to the different SL/BI equipment the LHC turn clock and a 32 bytes message (machine events, beam parameters, process request...).

Michel JONKER outlined that the possibility to transmit machine events through the BST/TTC system appears to be an interesting option. In this case, the LHC experiments   which are also connected to the TTC system, will be able to receive easily machine events.

Jean-Jacques SAVIOZ concluded that the solution to base the LHC BST distribution on the TTC system appears to be today the most suitable approach. A final proposition will be done by SL/BI end of 2000 and final acceptance tests will be performed early in 2001.

10MHz distribution

After the requirement from SL/HRF for a CERN wide fine time reference over all machines (CPS, SPS, LHC) (see minutes), Gary BEETHAM presented the work done by SL/CO and PS/CO on a CERN wide distribution of the CPS 10MHz frequency (see slides attached). He concluded that the the 10MHz can be transmitted over multi-mode fiber from the PS to the SL/HRF faraday cage in BA3 with sufficient phase and frequency stability. Nevertheless, the synchronization (re-synchronization) with the GPS "one pulse per second" clock requires more study. Philipppe BAUDRENGHIEN reminded that SL/HRF is mostly interested by a good frequency stability and accepted the results presented.

LHC slow timing possibilities

Michel JONKER reviewed the LHC slow timing possibilities and identified four possible ways to implement slow timing distribution:

1. Classical,
2. BST based,
3. Based on absolute time,
4. Replaced by RT system.

For each type of distribution, he reviewed the pros and the cons (see slides attached) and concluded that:

• "If you are going to do something fancy, try the slow timing ‘irradication’ first (... use of RT system),
• the BST options seems to be very promising and has the advantage to distribute the events signals also to the experiments,
• Otherwise, best bet is the classical system."

Philippe BAUDRENGHIEN reminded that SL/HRF requires a classical slow timing system for the control of the LHC-RF equipment and that proposed solution has to fulfil the equipment group requirements and not impose incompatible technical approach. Michel JONKER explained that slow timing distribution can be different during different LHC operating mode. He explained that LHC injection related slow timing signals can be generated by the SPS slow timing system and that it is already foreseen to distribute these signals to the LHC-RF.

Gary BEETHAM concluded that more inputs are necessary in order to evaluate the different propositions of Michel JONKER. He has asked Robin LAUCKNER to present his vision of slow timing requirements in the frame of the LHC-CP project at the next meeting.

AOB

Philippe BAUDRENGHIEN outlined that TTC transmission system required a manual reset if the distribution of the 40MHz is interrupted.  This approach is not compatible with a cycling machine like the SPS where RF has to be resynchronized before each elementary cycle. Simultaneously, SL/HRF would like to avoid to provide a signal when nobody use it or when the signal has no meaning. This is typically the case during the re-synchronization of the 40Mhz with the 400Mhz . Philippe BAUDRENGHIEN suggested that an automatic external resync pulse/mechanism has to be implemented in order to avoid the necessity of a manual action. It appeared rapidly unclear where this mechanism has to be implemented and who has the responsibility to realize it. Jean-Jacques SAVIOZ reminded that this necessary external reset causes problems to SL/BI for the evaluation of the BST/TTC system (see "BI progress with TTC") on the SPS-P2 cycle because of the necessity of a manual reset before each cycle. A long term solution has to be discussed with TTC project. Short term solution has to be found for next year SL/BI tests (Action Jean-Jacques SAVIOZ and Philippe BAUDRENGHIEN).

Next meeting

No meeting actually scheduled.