GlueX TOF Meeting, August 11, 2021
GlueX Time-of-Flight Meeting
Wednesday, August 11, 2021
10:00 am EDT
BlueJeans: 350 531 998
- Review of minutes from the last meeting
- PMT Repair
- Test of replaced PMTs
- FADC replacement
- TOF II Trigger
- TOF NIM paper
- Action Item Recap
Present: Edmundo Barriga, Eugene Chudakov, Mark Ito (chair), Sasha Ostrovidov, Susan Schadmand, Beni Zihlmann
Review of minutes from the last meeting
We went over the minutes of the meeting on June 30. 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.
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. 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.
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.
- Schedule time for testing the TOF II trigger.
- Do the HV scan and analyze the results.
- Replace the defective FADCs.