[Halld-pid] Minutes -- Re: Time-of-Flight Meeting, Tue. July 12, 11 am, F326/327, BlueJeans: 350 531 998

[Mark Ito]

Folks,

Please find the minutes below and at https://goo.gl/djmhb5 .

   -- Mark

__________________________________


    GlueX TOF Meeting, July 12, 2016, Minutes

Present:

  * *JLab*: Eugene Chudakov, Mark Ito (chair), Simon Taylor, Beni Zihlmann

There is a recording of this meeting <https://bluejeans.com/s/9ZDE/> on 
the BlueJeans site.


      Laser Tests

Beni reported on tests he has done with the laser.


        10-Stage Tube

  * Used a spare TOF tube.
  * At 1200 V, adjusted laser to give a 150 mV peak pulse. Can increase
    rate to 10 MHz with no reduction in gain.
  * At 1300 V, 150 mV pulse again. At 1 MHz start to see noise
    (extraneous pulses with low amplitude out of time). These could be
    due to the PMT heating up.
  * At 1400 V
      o 150 mV pulse: can go to 10 MHz without loss of amplitude.
      o 300 mV pulse: see loss in amplitude at 5 MHz.
      o 1.5 V pulse: start seeing loss somewhere between 1 and 2 MHz.
  * Behavior consistent with what was observed during the run in the
    difference in PMT gain between PARA and PERP for some runs. Rates
    were around 1 MHz and gains varied significantly when intensity
    changed with the polarization orientation.


        8-Stage Tube

  * Over the weekend Paul Eugenio, on his way through Newport News,
    dropped of an 8-stage tube in Beni's office.
  * At 1400 V, 150 mV pulse, start to see noise at 2 MHz and a drop in
    amplitude at 10 MHz.
  * At 1250 V, 150 mV pulse, less noise is seen at the higher rates and
    no drop in amplitude was seen.


      Discussion

  * Beni hopes to reduce gain by factor of 4 or 5.
  * HV settings already changed to 1250 V for all channels in Hall (from
    the various values around 1500 V we were using before).
  * On the scope he sees that the largest pulses of several Volts are
    reduced to about 700 mV, a factor of 3 or 4.
  * Eugene suggested we measure the gain curve (amplitude as a function
    of voltage for a fixed input light pulse). The can be used to
    estimate settings going forward.
  * Eugene pointed out that even with this reduction in voltage, when we
    go to high luminosity, we will right back in the same situation we
    were in during the last run. Some kind of action is necessary long-term.
  * The dynamic range on the ADCs needs to be changed from 2 V full
    scale to 0.5 V.
  * Beni wants to take some cosmics in the new configuration. These data
    can be compared with those that Sasha Ostrovidov took before the
    last run.
  * Eugene reminded us that we will have to study the effect of these
    changes on timing.
  * Beni found his old wiki page where he studied rates. In that he
    estimated that we should be aiming for 150 mV pulses from the center
    of the paddles if we want to have acceptable tube lifetimes.
  * A picture is emerging where the amplitude drop is not simply a
    function of current but rather depends on the PMT gain.


      Long-Term Planning

  * We need to explore options for replacing the bases, tubes, or both
    in all or part of the detector. Base modification would include an
    amplifier like that used on the tagger hodoscope. Beni will talk to
    Fernando Barbosa about options.
  * We will also have to consult with Tim Whitlatch on the mechanical
    work in the Hall. We will likely have to dismount the TOF from the
    FCAL frame to affect the changes. This could be done after the
    Spring run of 2017. There may be some schedule interference with
    DIRC installation during that time.
  * Mark contacted Ardavan Ghassemi of Hamamatsu for quotes on new
    tubes. Ardavan is traveling but should be back soon.

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  * This page was last modified on 13 July 2016, at 13:26.

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