GlueX TOF Meeting, June 28, 2016
GlueX Time-of-Flight Meeting
Tuesday, June 28, 2016
11:00 am EDT
JLab: CEBAF Center, Room F326/327
- Review of minutes from the previous meeting
- PMT Gains
- Calibration Status
- NIM paper: svn co https://halldsvn.jlab.org/repos/trunk/publications/GlueXTOF
- The BlueJeans Meeting number is 350 531 998.
- Enter BlueJeans Meeting
Talks can be deposited in the directory
/group/halld/www/halldweb/html/talks/2016 on the JLab CUE. This directory is accessible from the web at https://halldweb.jlab.org/talks/2016/ .
- FSU: Brad Cannon, Sasha Ostrovidov
- JLab: Eugene Chudakov, Mark Ito (chair), Simon Taylor, Tim Whitlatch, Beni Zihlmann
There is a recording of this meeting on the BlueJeans site.
PMT Gain Loss
Sasha showed some plots confirming the effect 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.