[Halld-pid] Time-of-Flight Meeting Minutes, June 28, 2016

[Mark Ito]

Folks,

Find the minutes below and at https://goo.gl/kJps11 .

   -- Mark
______________


  GlueX TOF Meeting, June 28, 2016, Minutes

Present:

  * *FSU*: Brad Cannon, Sasha Ostrovidov
  * *JLab*: Eugene Chudakov, Mark Ito (chair), Simon Taylor, Tim
    Whitlatch, Beni Zihlmann

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


      PMT Gain Loss

Sasha showed some plots confirming the effect 
<http://hadron.physics.fsu.edu/%7Eostrov/tof/20160628> that Beni 
presented at the last meeting. He looked at three runs, one from Spring 
2015, one from the beginning of the Spring 2016 run and one at the end 
of Spring 2016. He showed raw ADC distributions for a single channel and 
a scatter plot of ADC amplitude vs. channel. All roughly the same gain 
for the first two runs and lower gain, by varying amounts, depending on 
channel, for the last run. For the single channel, chosen to be one hear 
the beamline, the loss shown by the raw distribution is nearly 50%.

We discussed a variety of observations and ideas:

  * Beni reported that the rate on the thin counters near the beam line
    (those with the highest rate) was 1 to 1.5 MHz for later runs.
  * Tim recalled that FSU had a jig they used for gluing light guides to
    phototubes. We still have it here.
  * Four of the original PMTs were shipped from FSU to JLab. Beni has
    accounted for three of them. There are 10 PMTs at FSU installed as
    part of the mini-TOF (a prototype set-up). There are 176 installed
    on the TOF itself. [Added in press: the PO shows that 190 were
    indeed purchased.]
  * The PMTs are Hamamatsu H10534MOD and cost $1,015 each.
  * Beni will look for a low intensity run near the end of the Spring
    2016 run.
  * Last year, we increase the full-scale of the ADCs from 1 V to 2 V.
    Beni is thinking we should go to 0.5 V in the future.
  * The PMTs are run at various voltages, from 1,400 to 1,700 V. The
    tubes with the highest intrinsic gain are positioned near the
    beamline and are run at the low end of this range.
  * We will try to get schematics for the base from Hamamatsu.
  * We will get quotes from Hamamatsu on replacement 10-stage tubes and
    tubes with the same dimensions having 8 stages (Hamamatsu R7997).
  * Beni will get the laser test set-up going so we can test rate
    dependence.
  * The discriminator thresholds were set at 50 mV for the run.
  * Sasha will check to see if he has any 8-stage tubes at FSU.
  * Beni will consult with Fernando on an understanding of the active
    part of the divider circuit.
  * The bases designed for the tagger by Vladimir Popov have
    amplification of a factor of 8 on board. They are AC-coupled and so
    are subject to rate-dependent baseline shifts. We need to find out
    of AC-coupling is an essential feature of the design.
  * Sasha analyzed the voltage scan we did during the run. We should
    review that for hints on how to set the voltages going forward.

The major question to answer at this point is whether the loss of gain 
observed is due to intrinsic rate dependence (the rate at the end of the 
run is the highest that we took), or long-term deterioration of the last 
dynode. It is likely a combination, but the relative importance of each 
is component important for planning. If the last dynode is compromised, 
we should consider replacing tubes.

We agreed to meet again in a week, Tuesday, July 5, at 11 am.

Retrieved from 
"https://halldweb.jlab.org/wiki/index.php?title=GlueX_TOF_Meeting,_June_28,_2016&oldid=75897"

  * This page was last modified on 28 June 2016, at 15:37.


-- 
marki at jlab.org, (757)269-5295

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