[Halld-pid] Minutes, GlueX TOF Meeting, Sepbember 29, 2011

[Mark M. Ito]

Folks,

Find the minutes at 
http://www.jlab.org/Hall-D/software/wiki/index.php/GlueX_TOF_Meeting%2C_September_29%2C_2011#Minutes 
and below.

   -- Mark
   _______

GlueX TOF Meeting, September 29, 2011

Minutes

    Present:
      * FSU: Paul Eugenio, Sasha Ostrovidov
      * JLab: Chuck Hutton, Mark Ito (chair), Beni Zihlmann


Mechanical design

    We had another design meeting last Thursday, September 22 where Chuck
    showed [25]slides of his work in modifying the design to fit in the
    FCAL/TOF support structure. We reviewed some of those ideas. They
    appear to give us the needed clearance.

    Chuck has been working on the mechanical support for the TOF. He showed
    [26]some slides sketching ideas thus far, especially for holding the
    vertically-oriented plane.

    Chuck will call Ian Winger this afternoon to coordinate support design
    ideas.

PMT base design, rates, currents, amplification

    Beni led us through a revised version of his rate and PMT current
    studies. See his wiki page, [28]Detector Rates and Lifetime, for
    details. Since last time he has run Monte Carlo to get a better handle
    on the average energy of hits from electromagnetic background for
    counters at various positions in the array. He calculates currents
    assuming that the average pulse in each counter is 100 mV with a
    triangular pulse shape, 25 ns at the base.

    To get a better handle on the current, we need to know the number of
    photoelectrons per unit deposited energy in the counters. Sasha can
    measure this with the prototype if the tube gain is known. We noted
    that if he uses the Hamamatsu tubes at the "standard" voltage given in
    their documentation accompanying each tube and looks at the charge
    measured for minimum ionizing pulses, then we can rely on the gain
    published in the document, to the accuracy we need for these estimates,
    to get p.e.'s/MeV. Earlier Beni had measured the gain of one of these
    tubes and got a value very close to that in the documentation.

    It seems that we will have to do something about the high rate
    counters. Options include:
     1. running the tubes a lower gain
           + Paul mentioned a paper documenting this approach to reduce
             current with an XP2020 tube. He will send it to the email
             list.
     2. using 8-stage tubes rather than the nominal 10-stage tubes
     3. using amplifiers to increase the signal level after reducing gain
           + placing the amplifiers in the base
           + using external amplifiers
     4. a two-step mitigation plan with one configuration for running at
        10^7 and other for running at 10^8.

    Options may have to be combined.

    We need to decide on an approach soon since we must purchase the tubes
    now (essentially).

Prototype testing

    Sasha reported a couple of problems he is investigating right now.
      * The CAEN TDC will spontaneiously stop triggering. Sergey Boiarinov
        is also using this TDC and has not seen this problem.
      * One of the six PMT's, gives an anomalous signal shape about 15% of
        the time. The pulse rises slowly and returns to baseline slowly.
        These pulses are not likely to give good timing information.

    Sasha is currently getting a value of 110 ps resolution in mean time,
    per plane.

    paper on xp2020

    need photoelectons per mev can be measured with mips if tube gain is
    known

Contract status

    We have drafts of the SOW, the scintillator specification, the PMT
    specification, and several top-level drawings. All have been circulated
    within the working group. The next steps are to get the specifications
    signed and submit the package to Procurement.

    The PMT specification can be used as the basis for purchase by the Lab.

    Paul agreed to review the dates for milestones in the SOW once more.

Action Items

     1. Chuck will call Ian about mechanical support ideas.
     2. Sasha will measure the charge of minimum ionizing pulses with
        standard tube voltage.
     3. Paul will review the dates for milestones in the SOW.
     4. Mark will get the specifications signed.


Retrieved from 
http://www.jlab.org/Hall-D/software/wiki/index.php/GlueX_TOF_Meeting%2C_September_29%2C_2011

References

   25. https://halldweb1.jlab.org/talks/2011-3Q/tof%209_22_11.pptx
   26. https://halldweb1.jlab.org/talks/2011-3Q/tof_9_29_11.pptx
   28. 
http://www.jlab.org/Hall-D/software/wiki/index.php/Detector_Rates_and_Lifetime