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Folks,<br>
<br>
Find the minutes below and at <a class="moz-txt-link-freetext" href="https://goo.gl/kJps11">https://goo.gl/kJps11</a> .<br>
<br>
-- Mark<br>
______________<br>
<br>
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<h1 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">GlueX TOF Meeting, June 28, 2016, </span><span
class="mw-headline" id="Minutes">Minutes</span></h1>
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<p>Present:
</p>
<ul>
<li> <b>FSU</b>: Brad Cannon, Sasha Ostrovidov</li>
<li> <b>JLab</b>: Eugene Chudakov, Mark Ito (chair),
Simon Taylor, Tim Whitlatch, Beni Zihlmann</li>
</ul>
<p>There is a <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/9UzN/">recording of this
meeting</a> on the BlueJeans site.
</p>
<h3><span class="mw-headline" id="PMT_Gain_Loss">PMT Gain
Loss</span></h3>
<p>Sasha showed <a rel="nofollow" class="external text"
href="http://hadron.physics.fsu.edu/%7Eostrov/tof/20160628">some
plots confirming the effect</a> 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%.
</p>
<p>We discussed a variety of observations and ideas:
</p>
<ul>
<li> 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.</li>
<li> Tim recalled that FSU had a jig they used for
gluing light guides to phototubes. We still have it
here.</li>
<li> 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.]</li>
<li> The PMTs are Hamamatsu H10534MOD and cost $1,015
each.</li>
<li> Beni will look for a low intensity run near the end
of the Spring 2016 run.</li>
<li> 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.</li>
<li> 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.</li>
<li> We will try to get schematics for the base from
Hamamatsu.</li>
<li> We will get quotes from Hamamatsu on replacement
10-stage tubes and tubes with the same dimensions
having 8 stages (Hamamatsu R7997).</li>
<li> Beni will get the laser test set-up going so we can
test rate dependence.</li>
<li> The discriminator thresholds were set at 50 mV for
the run.</li>
<li> Sasha will check to see if he has any 8-stage tubes
at FSU.</li>
<li> Beni will consult with Fernando on an understanding
of the active part of the divider circuit.</li>
<li> 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.</li>
<li> Sasha analyzed the voltage scan we did during the
run. We should review that for hints on how to set the
voltages going forward.</li>
</ul>
<p>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.
</p>
<p>We agreed to meet again in a week, Tuesday, July 5, at
11 am.
</p>
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<pre class="moz-signature" cols="72">--
<a class="moz-txt-link-abbreviated" href="mailto:marki@jlab.org">marki@jlab.org</a>, (757)269-5295
</pre>
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