GlueX Start Counter Meeting, December 13, 2012

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GlueX Start Counter Meeting
Thursday, December 13, 2012
10 am EDT
JLab: CEBAF Center F326/327


  1. Announcements
  2. Review minutes from previous meeting
  3. Counter Construction
  4. SiPM read-out status
  5. Light collection study status
  6. Contract

Communication Information

Video Conferencing

Telephone and Desktop Sharing

To connect via telephone:

To view the shared desktop:


Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2012-4Q on the JLab CUE. This directory is accessible from the web at .



  • FIU: Eric Pooser
  • JLab: Eugene Chudakov, Mark Ito (chair), Puneet Khetarpal, Chuck Hutton, Beni Zihlmann

Review minutes from previous meeting

We went over the minutes from the November 29th meeting.

  • The ST-2 board should be coming back to FIU soon.
  • There are discriminators at JLab that could be lent to FIU. Mark has an email in to Fernando.
  • The CODA set-up at FIU
    • A trigger supervisor is running accepting triggers from a pulse generator.
    • There is no read-out of DAQ boards yet, read-out lists have not been downloaded yet. David Abbott will advise on which to use from list of model numbers already sent to him. Beni mentioned that the code might be found on /site/coda/3.0 at JLab.


Eric gave a report.

Bending scintillator at Eljen

Yesterday Eric had a conversation with Chuck Hurlbut, chief engineer at Eljen. They reviewed the start counter geometry and discussed types of heating methods. Chuck thought localized infra-red heating should be tried. He proposed using aluminum foid to cover areas that need not heated and to support the scintillator in its bent form on a polichs aluminum surface. He recommended trying for the minum heat necessary to bend the scintillator. He thought that it would relatively simple for Eljen to bend the scintillator before it is sent to McNeal for machining. If Eljen does the bending there would be no need for diamond-polished edges.

In the previous batch, McNeal removed the protectective tape to heat the counters for bending and so when machining was done there was no protection in that region with a resulting degradation in surface quality. Eljen would re-apply the protective tape over the entire surface before shipping to McNeal.

Eugene asked if can we leave the tape on the counters permanently. There was some concern that the tape might defeat internal reflection, but Eric will give it a try and test a counter with the tape on.

CLAS start counter experience

Eric has gone through the paper describing the CLAS start counter. He found a lot of interesting ideas in there and is now in contact with Youri Sharabian. They have already had some useful discussions.

Tests with wrapping materials

The current plan calls for 2-micron aluminum coated mylar. Eric will also try aluminum foil. In the past it is possible results were less than optimal due to wrapping the counters too tightly with Mylar.

Eric will also look at making each counter light tight. Beni will give some black Tedlar to bring back to FIU.

Questions on the drawings

Eric noticed, looking at finalized geometry, that the width of the counters has changed from a previous version. Chuck reported that he had discussed these same changes with Werner previously; they were necessary to accommodate the SiPM read-out boards in the space between the CDC and the target.

Eric asked Chuck to send him the drawing of the foam cone assembly in VXF or DWG format, not STP.

SiPM Read-out status

Eugene reminded us that we need to measure the amplitude of pulses from the counter in the SiPM to finalize the gain in the design. Eric is planning on doing that measurement as soon as he gets ST-2 back from JLab.

We will need amplitude information for time-walk corrections since we are using leading edge discriminators.


Mark is answering some final questions from Jarrod Fitzpatrick of Procurement so that the Request for Proposals can be issued to FIU.