Minutes 6-22-2007

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FDC Weekly Meeting

Date: June 22, 2007

Participants: Daniel, Simon, Brian, Kim, Roger, Tim, Chuck

Next Meeting: July 11, 2007

Cathode Updates

 - Brian sent out the Gerber file for our full-scale cathode boards
   to Optiprint and Sierra in the last week.  He heard back from 
   Optiprint that they cannot handle this request.  He expects word
   back from Sierra in the next week.
 - Our plan is that if Sierra cannot do this work, we will immediately
   go back to CCT Marketing and pay the $14k for setup charges and have
   them make the +/-75 deg boards for the small-scale prototype and
   also nominally plan on using them for the full-scale boards.
 - We do not presently have a plan to measure the flatness of our
   non-backed full-scale cathode prototype as the boards need to be
   measured when they are in a vertical orientation (so that gravity
   is eliminated).  We appear to have more options with the backed
   boards, which can be measured laying flat.
 - We discussed the plans for future cathode prototyping:
    > we will make one more prototype without backing focussing on the
      issues that arose during the first attempts.  We need to come up
      with plans to handle the alignment and overlap of the multi-piece
      cathodes and we need to be sure that the air-bubble problem is
    > we will make another prototype with backing, but with a reduce
      Rohacell thickness.  Our nominal thickness is 5-mm, but we believe
      that we can use less material here.  Brian will contact the
      manufacturer to find out what they can provide.  Tim will work
      on some calculations to compare the 5-mm thicknesses to 2 and 3-mm
      thicknesses.  The plan would be to use the thinner Rohacell plus
      a filler piece (to give a total thickness of 5-mm) during manufacture.
      After the cathode is glued in place, the filler material would be

Wire Frames

 - Brian has completed a full-scale prototype of a composite wire frame.
   His construction used two 1/32-in skins of G10 and a 5-mm thick
   Rohacell core.  The test appears to be a success and presents us with
   a viable wire frame that should be able to handle the wire load without
   significant distortion.  Brian will still perform a load test to
   give us more information (he would like to compare this to results
   that Tim can provide from calculation).
 - The weight of the 5-mm thick G10 frame is 7.9lbs and that of the
   composite is 2.9lbs.  This amounts to nearly a factor of 3 reduction
   in thickness of these boards.  Good news.
 - In the final composite design, the composite frame would be a total
   of 5-mm thick, and one side of the board would be tiled with the
   1/32-in STBs, HVTBs, and filler pieces.  (The Rohacell would need to
   be 3.4 mm thick.)

Magnetic Field Tests

 - DSC has taken some pictures of the magnet and surrounding area and
   will post them in the FDC logbook.
 - DSC has had discussions with Arne, and it appears that the mini-torus
   power supply can supply sufficient current to ramp the magnet to
   full-field regardless of its lead configuration.  Stepan plans on
   mapping field strength vs. current first thing in the shutdown period.
 - We are still in a bind with finding detectors to define an external
   track through the FDC prototype.  It appears we have talked to 
   all folks at JLab.  Brian will talk to folks at SLAC and BNL.  Simon
   will talk to Elke.
 - Simon and Brian have been talking with Bogdan from Hall A, and he
   has 3 2-cm diameter silicon detectors.  There is a fourth detector,
   but it is broken.  Simon will talk to Bogdan about whether these
   are single axis detectors.  If they are, then having only 3 detectors
   is insufficient.  Also, the small size is a big worry for us.  The
   counting rate will be miniscule.


 - Joe was going to provide some numbers on the thicknesses of the
   original readout cables and the modified (no-shield) version.  Simon
   will follow up with him to get this information.

Work List

 - The FDC short-term work list has been posted on the FDC web site
   (see http://www.jlab.org/Hall-D/detector/fdc/).  This is continually
   being updated and DSC welcomes any feedback or comments from the group.

Minutes prepared by Daniel. Send any comments or corrections along.