GlueX TOF Meeting, September 29, 2011
Thursday, September 29, 2011
10:00 am EDT
JLab: CEBAF Center, Room F326
- Minutes from the last meeting
- Mechanical design: Tim, Chuck
- PMT base design, rates, currents, amplification Beni
- Prototype status: Paul, Sascha
- Contract Status: Mark
Talks can be deposited in the directory
/group/halld/www/halldweb/html/talks/2011-3Q on the JLab CUE. This directory is accessible from the web at https://halldweb.jlab.org/talks/2011-3Q/ .
- FSU: Paul Eugenio, Sasha Ostrovidov
- JLab: Chuck Hutton, Mark Ito (chair), Beni Zihlmann
We had another design meeting last Thursday, September 22 where Chuck showed slides of his work in modifying the design to fit in the FCAL/TOF support structure. We reviewed some of those ideas. They appear to give us the needed clearance.
Chuck has been working on the mechanical support for the TOF. He showed some slides sketching ideas thus far, especially for holding the vertically-oriented plane.
Chuck will call Ian Winger this afternoon to coordinate support design ideas.
PMT base design, rates, currents, amplification
Beni led us through a revised version of his rate and PMT current studies. See his wiki page, Detector Rates and Lifetime, for details. Since last time he has run Monte Carlo to get a better handle on the average energy of hits from electromagnetic background for counters at various positions in the array. He calculates currents assuming that the average pulse in each counter is 100 mV with a triangular pulse shape, 25 ns at the base.
To get a better handle on the current, we need to know the number of photoelectrons per unit deposited energy in the counters. Sasha can measure this with the prototype if the tube gain is known. We noted that if he uses the Hamamatsu tubes at the "standard" voltage given in their documentation accompanying each tube and looks at the charge measured for minimum ionizing pulses, then we can rely on the gain published in the document, to the accuracy we need for these estimates, to get p.e.'s/MeV. Earlier Beni had measured the gain of one of these tubes and got a value very close to that in the documentation.
It seems that we will have to do something about the high rate counters. Options include:
- running the tubes a lower gain
- Paul mentioned a paper documenting this approach to reduce current with an XP2020 tube. He will send it to the email list.
- using 8-stage tubes rather than the nominal 10-stage tubes
- using amplifiers to increase the signal level after reducing gain
- placing the amplifiers in the base
- using external amplifiers
- a two-step mitigation plan with one configuration for running at 107 and other for running at 108.
Options may have to be combined.
We need to decide on an approach soon since we must purchase the tubes now (essentially).
Sasha reported a couple of problems he is investigating right now.
- The CAEN TDC will spontaneiously stop triggering. Sergey Boiarinov is also using this TDC and has not seen this problem.
- One of the six PMT's, gives an anomalous signal shape about 15% of the time. The pulse rises slowly and returns to baseline slowly. These pulses are not likely to give good timing information.
Sasha is currently getting a value of 110 ps resolution in mean time, per plane.
paper on xp2020
need photoelectons per mev can be measured with mips if tube gain is known
We have drafts of the SOW, the scintillator specification, the PMT specification, and several top-level drawings. All have been circulated within the working group. The next steps are to get the specifications signed and submit the package to Procurement.
The PMT specification can be used as the basis for purchase by the Lab.
Paul agreed to review the dates for milestones in the SOW once more.
- Chuck will call Ian about mechanical support ideas.
- Sasha will measure the charge of minimum ionizing pulses with standard tube voltage.
- Paul will review the dates for milestones in the SOW.
- Mark will get the specifications signed.