[Halld-pid] Time-of-Flight Meeting Minutes, August 11, 2021

[Mark Ito]

Friend,

Please find the minutes here 
<https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_August_11,_2021#Minutes> 
and below.

   -- Mark

      ____________________________________


    GlueX TOF Meeting, August 11, 2021, Minutes

Present: Edmundo Barriga, Eugene Chudakov, Mark Ito (chair), Sasha 
Ostrovidov, Susan Schadmand, Beni Zihlmann

There is a recording of this meeting 
<https://bluejeans.com/s/p94Csgi@3CM/>. Log into the BlueJeans site 
<https://jlab.bluejeans.com> first to gain access (use your JLab 
credentials).


      Review of minutes from the last meeting

We went over the minutes of the meeting on June 30 
<https://halldweb.jlab.org/wiki/index.php/GlueX_TOF_Meeting,_June_30,_2021#Minutes>. 
Paul and Edmundo brought some PMTs from FSU. In the process of marking 
PMTs as returned on the loan agreement (JLab to FSU) we ran into a 
complication in the accounting that will not be described here. 
Negotiations are in progress.


      PMT Replacement

Edmundo reported on the repair trip he and Paul Eugenio made to JLab, 
July 12-16. Four tubes were replaced. The only difficulty encountered 
was that the "PMT clipper" used to break the joint between PMT and light 
guide was designed for TOF I and had to have some field mods to work 
with some of the TOF II tubes. Other that that, the operation went 
smoothly.

After the work was done Beni turned on all of the HV and saw scalars 
counting for all of the channels save one. He later found a cable not 
bayoneted into the splitter; re-seating it fixed the channel.


      Plans for HV Scan

Beni has created the voltage configuration files for an HV scan. 
Voltages are uniform across the array in each file and files have been 
produced in 25 V increments from 1175 to 1375 V. The code to analyze the 
data looks for minimum ionizing peaks and fits an exponential to the 
peak position as a function of voltage. With these fits we can pick a 
gain-balanced operating point. The software needs to be checked to see 
if it still works with recent releases.


      Test of replaced PMTs

Sasha has looked at the four PMTs removed from the TOF. He led us 
through his web page summarizing results 
<http://hadron.physics.fsu.edu/~ostrov/tof/20210802/>. He uses a UV LED 
and measures the position of the single-photoelectron peak with the HV 
set at 1750 V. He can then compare with the same measurement performed 
before the PMT was included in a module assembly years ago. The tubes 
show a reduction in gain of about a factor of two. This is significant, 
but not a cause for panic, even though other tubes still in the array 
may suffer from the same loss in gain.


      FADC Replacement

Beni is talking to the electronics guys about getting four FADC-250s to 
replace the ones that have a bad bit in the DAC for certain channels, 
one channel per board as it turns out. He is hopeful that the spares 
will be found and we can do the replacement before the run.


      Actions Items

 1. Schedule time for testing the TOF II trigger.
 2. Do the HV scan and analyze the results.
 3. Replace the defective FADCs.


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