GlueX Start Counter Meeting, September 5, 2013
GlueX Start Counter Meeting
Thursday, September 5, 2013
10 am EDT
JLab: CEBAF Center F326/327
- Review minutes from previous meeting
- Construction Status
- Electronics Status
- Installation planning
- US and Canada: (866)740-1260 (toll free)
- International: (303)248-0285 (toll call) or look up toll-free number at http://www.readytalk.com/intl
- enter access code followed by the # sign: 1833622#
- Go to http://esnet.readytalk.com
- In the "join a meeting" box enter the Hall D code: 1833622
- Fill in the participant registration form.
Talks can be deposited in the directory
/group/halld/www/halldweb/html/talks/2013-3Q on the JLab CUE. This directory is accessible from the web at https://halldweb.jlab.org/talks/2013-3Q/ .
- FIU: Werner Boeglin, Eric Pooser
- JLab: Chuck Hutton, Mark Ito (chair), Tim Whitlatch
You can find a recording of the meeting at the ReadyTalk site. It will be there for about a month.
Review of the Last Meeting
We reviewed the minutes of the meeting we had on August 22.
- Mark discussed the issue of SiPM placement tolerance with Fernando. He thinks he can hold the placement to about a mil which is much better than we require (the scintillators are 3 mm thick).
- We discussed when would be a good time for Nick Sandoval to do the initial electronics installation at FIU, as Fernando has proposed. This depends on how construction of the counters proceeds and what we want to get out of Nick's trip. We will have to discuss further in the future, with Fernando in the loop.
Foam Support Construction
Chuck spoke to Steve Christo of Hall B about what type of foam to use. Although they used Last-A-Foam for their start counter support, Steve recommended using Rohacell instead. Chuck contacted the company and obtained a quote for the 51 HF foam. The structure would be made of two "half-pipes" glued together. We are also considering the 71 HF which is mechanically stronger, but because of the size of their stock it would have to be made of three sections. The total cost is about $5,000, where the costs are dominated by engineering and set-up costs. An additional complete support assembly would only be another $300.
Tim has done some stress calculation and we would have to be somewhat careful that we do not apply too much "bending" force on the support cylinder. Werner mentioned to support a scintillating fiber array for Fermilab's D0 detector, a layer of carbon fiber was glued to a foam structure to increase strength. Tim will study adding a 1/2 mm carbon fiber layer. Although it would do more good on the outside of the foam, construction would be easier if it were placed on the inside. Werner pointed out that the carbon fiber could stop before the nose part of the counters and still add a lot of strength.
Werner mentioned that the position of each counter may have to be shimmed to get good alignment with the SiPMs. This can be done with layers of reflective material, probably VM2000. The nominal position increment to be added needs to be calculated and sent to Chuck soon so that he can put that into the design.
Eric gave us an update.
- The test stand is being constructed now. The SiPM case is done, the outer frame is being machined now. The holder for the scintillator and PMT case are next. It should be done by next week.
- A new quote was obtained from Eljen for the scintillator. For quantity 50 they will be $197 each, which is a bit better than the previous quote. FIU is nearly ready to proceed with the procurement.
- Eric spoke with Robert McNeal about buffing scratches observed on the broad faces of the prototype counters. The protective plastic that was applied by Eljen had to be removed to place the scintillator into the machining fixture. After machining, a new protective plastic film was applied before shipping to FIU. The claim is that the broad faces were never touched during this process. The quality of the edges, the surface that is actually machined, is very good. Eric also asked about how they verify dimensions and was told they use a coordinate-measuring machine that they have on hand there.
Construction of the SiPM boards will start very soon according to Fernando. Nick Sandoval will be doing the work. They have already done the bias-voltage-requirement matching of the SiPMs in groups of five, only four of which are needed for a particular channel. Recall that the design uses one bias voltage for all four SiPMs.