[Halld-pid] Minutes, GlueX TOF Meeting, October 13, 2011

[Mark M. Ito]

Folks,

Find the minutes at 
https://halldweb1.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_October_13,_2011#Minutes 
and below as text.

   -- Mark
   _____

GlueX TOF Meeting, October 13, 2011

Minutes

    Present:
      * FSU: Paul Eugenio, Sasha Ostovidov
      * JLab: Mark Ito (chair), Elton Smith, Simon Taylor, Beni Zihlmann

Mechanical Design

    Chuck Hutton and Ian Winger have had difficulty getting together to
    discuss changes to the light guides. Chuck should try and give Ian a
    call next week after he (Chuck) returns from vacation.

PMT base design, rates, currents, amplification

    We discussed several issues around handling the high-rate counters in
    the TOF array.
      * Paul pointed out that there a lot of uncertainties that make it
        hard to plan. We do not have firm numbers from Hamamatsu on tube
        lifetime and the rate calculations are only estimates.
      * Elton said that the uncertainties are large, but are "only" about a
        factor of 2 or so whereas the current estimates are too high by a
        factor of 20 or more. Moreover, rate estimates from Monte Carlo
        tend to underestimate the reality.
      * Elton mentioned that if we decide on a plan where tubes have to be
        replaced, we should consider not gluing them to the light guides.
      * If we have to run at reduced tube gain then it makes sense to do so
        with a lower gain tube, rather than reducing the HV on a high gain
        tube, i. e., we should consider the 8-stage Hamamatsu tube
        (H10570).
      * At a photon flux of 10^7/s the problem is obviously much less that
        at 10^8/s. We could consider some sort of two stage plan.
      * Beni proposed doing a study with a lower gain, corresponding the
        the 8-stage tube at a level that produces acceptable lifetime, to
        see if there is an efficiency issue with hits from the far end of
        the counter if amplifiers are not used.
      * Paul has two of the 8-stage tubes. He and Sasha will take a look at
        them and compare to the performance of the 10-stage tubes they have
        been focusing on.
      * Paul reports that the 10-stage and the 8-stage package of tube,
        divider, and shield from Hamamatsu have the same external
        dimensions. This means that mechanical design can proceed
        independent of the final decision on which tubes to purchase.
      * We reviewed the criteria Beni used to choose the "high-rate"
        modules. Effectively he draws the line between counter 17 at 1 MHz
        and counter 18 at 2 MHz in the estimate. That means two standard
        size counters (18 and 19 on one side, 26 and 27 on the other) on
        each side of the beam hole are considered high-rate. See
        "[29]Detector Rates and Lifetime" for details.
      * Given this choice, in total 40 of the 176 total tubes are for
        high-rate counters. See the "[30]Time-of-Flight Cheat Sheet" for
        details of the count.
      * The consensus proposal, given our current understanding, is to buy
        8-stage tubes for the high-rate counters and stay with 10-stage
        tube. If possible we will run at 10^7/s without amplifiers on the
        high-rate counters and design an amplification scheme for use at
        10^8/s.

Contract Status

    Paul will develop a more realistic timeline on which to hang
    milestones called out in the Statement of Work. He is concerned that
    the light guide production schedule is not accounted for realistically
    now. Both the production of the raw plastic cylinders by the
    manufacturer and the milling into light guides at by the FSU shop have
    to be taken into account.

    Mark asked if the uncertainty in the PMT choice is an empediment to
    going forward with the construction contract. Elton thought not,
    especially since the tubes will be bought by JLab.

Prototype Status

    Sasha showed [33]single-shot scope traces of pulses with and without
    back termination at the PMT of 50 Ohms. The non-terminated set-up
    showed a clear reflection and judging from the cable lengths it is
    coming from the splitter. Sasha will check the resistance of the
    various components and we will check the schematics at JLab to make
    sure they make sense.

Retrieved from 
https://halldweb1.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_October_13,_2011

References

   29. https://halldweb1.jlab.org/wiki/index.php/Detector_Rates_and_Lifetime
   30. https://halldweb1.jlab.org/wiki/index.php/Time-of-Flight_Cheat_Sheet
   33. https://halldweb1.jlab.org/talks/2011-4Q/Termination%20at%20PMT.html