[Halld-pid] Minutes, Start Counter Meeting, March 6, 2012

[Mark M. Ito]

Folks,

Find the minutes at 
https://halldweb1.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_March_6,_2012#Minutes 
and below as text.

   -- Mark
   _____

GlueX Start Counter Meeting, March 6, 2012
Minutes

    Present:
      * 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.

    Retrieved from
    
"https://halldweb1.jlab.org/wiki/index.php/GlueX_Start_Counter_Meeting,_March_6,_2012"

-- 
Mark M. Ito
Jefferson Lab (www.jlab.org)
(757)269-5295