GlueX Start Counter Meeting, March 6, 2012

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GlueX Start Counter Meeting
Tuesday, March 6, 2012
10 am EST
JLab: ARC, Room 428


  1. Announcements
  2. Review minutes from previous meeting
  3. Prototype Report
  4. Contract Status
  5. Simulation

Communication Information

Video Conferencing


Talks can be deposited in the directory /group/halld/www/halldweb/html/talks/2012-1Q on the JLab CUE. This directory is accessible from the web at .

Chair's Cell Phone




  • FIU: Werner Boeglin, Lei Guo
  • JLab: Chuck Hutton, Mark Ito (chair), Tim Whitlatch

Prototype Status

The first sample counter from McNeal is due in on March 14.

Mechanical Design

Chuck walked us through the 3-D drawing of the current mechanical concept. A lot of discussion was generated.

  • We discussed how to maintain the required accuracy of placement of the SiPM read-out boards with respect to the scintillator bars in both the in transverse and longitudinal dimensions.
    • Tim suggested that set screws to set longitudinal gap between scintillator and SiPM.
    • Werner pointed out that the critical dimension is in radial dimension since any mis-match loses light. He estimates we should control that dimension to about 200 microns.
    • Chuck pointed out that if we have more that three sections on the SiPM read-out boards, it would allow finer grained adjustment of position.
    • If there adjusts for position, we need to design in a way to tell that we are in good alignment.
  • To optically isolate the counters reflective material will be inserted between them. They will likely not be light-tight on a counter-by-counter basis.
  • Broadly, the construction concept we agreed on was to start with a precision machined rohacell inner shell, place counters around that shell, and apply the outer shell to that assembly. Then the complete assembly will be attached to the target support structure (aluminum or stainless).
  • We need to look at the Hall B support scheme for reference.
  • Tim pointed out that we would like to avoid using the target scattering chamber as a support structure for the nose section since any pressure on it could cause vacuum leaks.
  • Werner suggested that the whole start counter assembly could be held with springs against the target support structure.
  • Werner cautioned us not to forget the need for temperature stabilization for SiPM's.
    • Tim suggested that perhaps we can test ideas using Sascha Somov's SiPM samples.
  • We suffered somewhat by not having Fernando present for discussion of mechanical considerations for the read-out boards. Chuck will get together with Fernando this week and walk him through the current thinking. He will raise the temperature control requirements with him as well.

Contract Status

We need to get started on a statement of work.

New Action Items

  1. Research Hall B start counter mounting scheme.
  2. Talk to Fernando about mechanical issues with the read-out board.

Next meeting: March 22, 2012