GlueX TOF Meeting, October 13, 2011
Thursday, October 13, 2011
10:00 am EDT
JLab: CEBAF Center, Room F326
- Minutes from the last meeting
- Mechanical design: Tim
- PMT base design, rates, currents, amplification Beni
- Prototype status: Paul, Sasha 
- Contract Status: Mark
Talks can be deposited in the directory
/group/halld/www/halldweb/html/talks/2011-4Q on the JLab CUE. This directory is accessible from the web at https://halldweb.jlab.org/talks/2011-4Q/ .
- FSU: Paul Eugenio, Sasha Ostovidov
- JLab: Mark Ito (chair), Elton Smith, Simon Taylor, Beni Zihlmann
Chuck Hutton and Ian Winger have had difficulty getting together to discuss changes to the light guides. Chuck should try and give Ian a call next week after he (Chuck) returns from vacation.
PMT base design, rates, currents, amplification
We discussed several issues around handling the high-rate counters in the TOF array.
- Paul pointed out that there a lot of uncertainties that make it hard to plan. We do not have firm numbers from Hamamatsu on tube lifetime and the rate calculations are only estimates.
- Elton said that the uncertainties are large, but are "only" about a factor of 2 or so whereas the current estimates are too high by a factor of 20 or more. Moreover, rate estimates from Monte Carlo tend to underestimate the reality.
- Elton mentioned that if we decide on a plan where tubes have to be replaced, we should consider not gluing them to the light guides.
- If we have to run at reduced tube gain then it makes sense to do so with a lower gain tube, rather than reducing the HV on a high gain tube, i. e., we should consider the 8-stage Hamamatsu tube (H10570).
- At a photon flux of 107/s the problem is obviously much less that at 108/s. We could consider some sort of two stage plan.
- Beni proposed doing a study with a lower gain, corresponding the the 8-stage tube at a level that produces acceptable lifetime, to see if there is an efficiency issue with hits from the far end of the counter if amplifiers are not used.
- Paul has two of the 8-stage tubes. He and Sasha will take a look at them and compare to the performance of the 10-stage tubes they have been focusing on.
- Paul reports that the 10-stage and the 8-stage package of tube, divider, and shield from Hamamatsu have the same external dimensions. This means that mechanical design can proceed independent of the final decision on which tubes to purchase.
- We reviewed the criteria Beni used to choose the "high-rate" modules. Effectively he draws the line between counter 17 at 1 MHz and counter 18 at 2 MHz in the estimate. That means two standard size counters (18 and 19 on one side, 26 and 27 on the other) on each side of the beam hole are considered high-rate. See "Detector Rates and Lifetime" for details.
- Given this choice, in total 40 of the 176 total tubes are for high-rate counters. See the "Time-of-Flight Cheat Sheet" for details of the count.
- The consensus proposal, given our current understanding, is to buy 8-stage tubes for the high-rate counters and stay with 10-stage tube. If possible we will run at 107/s without amplifiers on the high-rate counters and design an amplification scheme for use at 108/s.
Paul will develop a more realistic timeline on which to hang milestones called out in the Statement of Work. He is concerned that the light guide production schedule is not accounted for realistically now. Both the production of the raw plastic cylinders by the manufacturer and the milling into light guides at by the FSU shop have to be taken into account.
Mark asked if the uncertainty in the PMT choice is an empediment to going forward with the construction contract. Elton thought not, especially since the tubes will be bought by JLab.
Sasha showed single-shot scope traces of pulses with and without back termination at the PMT of 50 Ω. The non-terminated set-up showed a clear reflection and judging from the cable lengths it is coming from the splitter. Sasha will check the resistance of the various components and we will check the schematics at JLab to make sure they make sense.
- Chuck call Ian. -> Chuck
- Study efficiency of a lower gain tube. -> Beni
- Send response to Hamamatsu guy. -> Mark
- Write new milestones for the SOW. -> Paul
- Check for resistances in the splitters. -> Sasha
- Check schematic for the splitters. -> Mark