[Halld-pid] Start Counter Meeting Minutes, May 29, 2014

[Mark M. Ito]

Folks,

Find the minutes below and at

https://halldweb1.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_May_29,_2014#Minutes 
.

   -- Mark
____________________________________________________

GlueX Start Counter Meeting, May 29, 2014
Minutes

    Present:
      * FIU: Werner Boeglin, Eric Pooser
      * JLab: Fernando Barbosa, Eugene Chudakov, Chuck Hutton, Mark Ito
        (chair), Nick Sandoval, Beni Zihlmann

Nick's Trip to FIU

      * We set a target date of the week after the Fourth of July holiday.
      * Werner has all of the read-out electronics he needs at FIU. The
        MPOD does need to be shipped to support testing.
      * We decided to ship all of the cables that connect ST2 to ST3 to
        FIU.
      * We will ship 10 sets of cables (for 10 counters) for testing. These
        are the full length cables that will be used in the Hall. Fernando
        points out that this will give more realistic test results.
      * Nick will bring a hand-held 4-channel thermister read-out device
        with him. Other multi-meters are available at FIU for use after he
        leaves.

Construction Status

    Eric gave the report.
      * The 50 scintillators are on their way to FIU from McNeal. They
        should arrive later today.
      * Eric has looked at the measurement data from McNeal. They look
        nominal.
      * Ibrahim at McNeal told Eric that there was no need to remove the
        protective adhesive machining.
      * The assembly jig is ready to go.

Support Structure Construction Status

    Chuck gave the report.
      * The aluminum support rings are in hand. A test fit of the
        electronics on one of the rings was successful.
      * The final machined Rohacell is due in tomorrow.
      * The carbon fiber inner support is ready to go.
      * The support assembly will all be glued together next week.

Schedule Review

    We thought that the readiness review should be scheduled for the end of
    June, before Nick's trip. By then FIU will have had an initial look at
    any assembly issues.

Testing Individual SiPMs

    We discussed techniques for ensuring that all four SiPMs in a read-out
    channel are contributing to the signal. All sets of four share a single
    bias voltage and are summed into a single pre-amp. The tests with the
    laser used a diffuser that illuminated all four at the same time. There
    is also concern that during the various assembly stages, connections on
    the board my get broken. When the detector is completely assembled
    there access to the SiPMs one at a time is blocked by the scintillator
    counters themselves. We decided on the following steps.
      * Nick will devise a method for doing a laser test of the SiPMs one
        at a time. This tells us that all four SiPMs are contributing, at
        least at the pre-assembly stage.
      * We will record record current for each channel. If these shift in
        the near future, then that will be an indication that a SiPM has
        become uncoupled. Over the long-term it may to hard to maintain
        this as a useful technique due to changes in the SiPMs themselves,
        due to radiation for example.

    Mark pointed out that we made some decisions early on to save money and
    simplify construction that preclude simple checking of the performance
    of individual SiPMs and that this was recognized at the time. Nothing
    we know now invalidates those conclusions.

Bias Voltage Control

    Fernando asked about the the control system for the bias voltages. Mark
    will check with Hovanes Egiyan on the status.

Light Tighting Issues

    Eric and Chuck have discussed the issue of keeping the detector light
    tight from the upstream end. We have to make a definite plan on how to
    do this and still allow for air flow to cool the electronics.