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<p>Folks,</p>
<p>Please find the minutes below and at <a class="moz-txt-link-freetext" href="https://goo.gl/djmhb5">https://goo.gl/djmhb5</a> .</p>
<p> -- Mark</p>
<p>__________________________________</p>
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<h2 id="firstHeading" class="firstHeading" lang="en"><span
dir="auto">GlueX TOF Meeting, July 12, 2016, </span><span
class="mw-headline" id="Minutes">Minutes</span></h2>
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lang="en">
<p>Present:
</p>
<ul>
<li> <b>JLab</b>: Eugene Chudakov, Mark Ito (chair),
Simon Taylor, Beni Zihlmann</li>
</ul>
<p>There is a <a rel="nofollow" class="external text"
href="https://bluejeans.com/s/9ZDE/">recording of this
meeting</a> on the BlueJeans site.
</p>
<h3><span class="mw-headline" id="Laser_Tests">Laser Tests</span></h3>
<p>Beni reported on tests he has done with the laser.
</p>
<h4><span class="mw-headline" id="10-Stage_Tube">10-Stage
Tube</span></h4>
<ul>
<li> Used a spare TOF tube.</li>
<li> At 1200 V, adjusted laser to give a 150 mV peak
pulse. Can increase rate to 10 MHz with no reduction
in gain.</li>
<li> 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.</li>
<li> At 1400 V
<ul>
<li> 150 mV pulse: can go to 10 MHz without loss of
amplitude.</li>
<li> 300 mV pulse: see loss in amplitude at 5 MHz.</li>
<li> 1.5 V pulse: start seeing loss somewhere
between 1 and 2 MHz.</li>
</ul>
</li>
<li> 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.</li>
</ul>
<h4><span class="mw-headline" id="8-Stage_Tube">8-Stage
Tube</span></h4>
<ul>
<li> Over the weekend Paul Eugenio, on his way through
Newport News, dropped of an 8-stage tube in Beni's
office.</li>
<li> At 1400 V, 150 mV pulse, start to see noise at 2
MHz and a drop in amplitude at 10 MHz.</li>
<li> At 1250 V, 150 mV pulse, less noise is seen at the
higher rates and no drop in amplitude was seen.</li>
</ul>
<h3><span class="mw-headline" id="Discussion">Discussion</span></h3>
<ul>
<li> Beni hopes to reduce gain by factor of 4 or 5.</li>
<li> HV settings already changed to 1250 V for all
channels in Hall (from the various values around 1500
V we were using before).</li>
<li> On the scope he sees that the largest pulses of
several Volts are reduced to about 700 mV, a factor of
3 or 4.</li>
<li> 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.</li>
<li> 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.</li>
<li> The dynamic range on the ADCs needs to be changed
from 2 V full scale to 0.5 V.</li>
<li> 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.</li>
<li> Eugene reminded us that we will have to study the
effect of these changes on timing.</li>
<li> 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.</li>
<li> A picture is emerging where the amplitude drop is
not simply a function of current but rather depends on
the PMT gain.</li>
</ul>
<h3><span class="mw-headline" id="Long-Term_Planning">Long-Term
Planning</span></h3>
<ul>
<li> 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.</li>
<li> 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.</li>
<li> Mark contacted Ardavan Ghassemi of Hamamatsu for
quotes on new tubes. Ardavan is traveling but should
be back soon.</li>
</ul>
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