GlueX TOF Meeting, July 5, 2016

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GlueX Time-of-Flight Meeting
Tuesday, July 5, 2016
11:00 am EDT
JLab: CEBAF Center, Room F326/327

Agenda

  1. Announcements
  2. Review of minutes from the previous meeting
  3. PMT Gains
  4. Calibration Status
  5. NIM paper: svn co https://halldsvn.jlab.org/repos/trunk/publications/GlueXTOF

Communication

Slides

Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2016 on the JLab CUE. This directory is accessible from the web at https://halldweb.jlab.org/talks/2016/ .

Minutes

Present:

  • FSU: Brad Cannon, Sasha Ostrovidov
  • JLab: Mark Ito (chair), Simon Taylor, Beni Zihlmann

There is a recording of this meeting on the BlueJeans site.

Review of minutes from the previous meeting

We skimmed the minutes from June 28.

  • Turns out we purchased 194 PMTs altogether, but 4 of them were for Elton to use (on a non-TOF project). Thus the 190 for the TOF use is correct. One tube was broken at the FSU machine shop. 3 spares were found by Beni in the cabinet in the hall, 10 are in the mini-TOF at FSU. 176 are part of the TOF. It all adds up.
  • Mark has a call into Ardavan Ghassemi at Hamamatsu asking for quotes on 10-stage and 8-stage tubes.
  • Sasha found an 8-stage tube at FSU. Paul Eugenio claims (via email) than an 8-stage tube was sent to Elton at some point.

PMT Gain Loss

Gain Studies

Beni described his write-up (previously this section was in the agenda section of this page).

  1. The following plots show the signal peak amplitude for hits that are matched to tracks
    the data are from different runs where we did a beam current scan starting with 40nA and going up to 150nA. At 40nA beam current the peak amplitudes look still reasonable, but already at 80nA a degradation is noticeable which becomes critical at even higher currents(luminosities). The radiator was 50um diamond. These data were taken near the end of the run. There is no correction for position/attenuation.
    • Run 11634 with 40nA beam current:
      Adc peak run11634.gif
    • Run 11635 with 80nA beam current:
      Adc peak run11635.gif
    • Run 11637 with 110nA beam current:
      Adc peak run11637.gif
    • Run 11636 with 150nA beam current:
      Adc peak run11636.gif
  2. The degradation of the PMTs over the spring run period is illustrated with the following plots showing the RAW ADC Signal amplitudes for an early run (run 10346) and a late run (run 11634 same as above low current 40nA)
    • Raw TOF data Signal amplitude RUN 10346 (left) track matching hits (right):
      Tofpmt amp raw run10346.gif Adc peak run10346.gif
    • Raw TOF data Signal amplitude RUN 11634 (left) track matching hits (right)::
      Tofpmt amp raw run11634.gif Adc peak run11634.gif

So there is both a severe rate dependence and long-term degradation of the gain. Sasha noted that the beginnings of this effect was visible in the Spring 2015 data.

Current PMT HV

Sasha put together a histogram of the current HV settings:
Current HV settings.png

Discussion

  • Beni has been looking at signals in the Hall. He sees many large (2 V) pulses. He will continue to explore reasonable running parameters.
  • Beni talked to Tom about the mechanical procedure for replacing tubes. We would need to build a jig hold the PMT to the light guide during gluing. He sketch an idea with springs to hold the PMT to a clamp around the light guide.
  • The nominal scheme Beni would like to try is:
    1. Reduce the HV to get a gain reduction of about a factor of four.
    2. Reduce the discriminator threshold to 15 mV from 50 mV.
    3. Reduce the ADC range maximum from 2 V to 0.5 V (this can be done by changing a jumper on the boards).
  • Sasha will look into reviving his test set-up at FSU. He could then look at efficiency and timing with lower voltages and thresholds.
  • We wondered if we could do similar tests with the TOF in the Hall with cosmics. No easy ideas presented themselves.
  • Beni pointed out the plateau curves on the TOF wiki pages. Turns out that these were done at IU a long time ago and the tubes are not clearly identified making them hard to interpret.
  • Sasha did some plateau curves on 10-stage and 8-stage tubes at one point. He presented them at a collaboration meeting. He will try to dig up the talk.
  • We decided to try plateau-ing the counters in the Hall using the discriminator scalers. Even with cosmics, this should be possible. It could even be automated, potentially.
  • Beni has got the laser box now. He will set-up a rate test.