Minutes 2-14-2007

FDC Weekly Meeting

Date: February 14, 2007

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

Next Meeting: Wednesday, February 21, 2007 @ 1:30 p.m.

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1). Drift Chamber Review:

 - As previously announced, the GlueX drift chambers (FDC and CDC) will
   be undergoing an external review on Mar. 6, 2007.  Folks have been
   asked to provide brief write-ups of various sections (Brian - bas,
   sandwich construction, cathode flatness measurement, Tim - sag,
   cooling, stress calculations, thermal calculations, Fernando -
   preamps, daughter boards, cooling) for the FDC technical design
   report.  Folks will also be asked to provide up-to-date drawings for 
   the FDC design.  This documentation is an essential part of the
   review.
 - Folks should make sure that they go over the posted talks and
   provide feedback on any issues that are unclear or (gasp) presented
   incorrectly.
 - Folks should also make sure that they are available to attend 
   the practice talks and, of course, the real talks to assist in
   answering questions that come up.

2). Cathode Mechanical Mockups:

 - Brian has completed the construction of the first dummy cathode
   sandwich mechanical mock-up.  The flatness of the cathode was
   measured by the JLab Survey Group using their Faro laser tracker.
 - The measurements had an accuracy of about 50 microns.  The
   measurement results were quite encouraging and demonstrated 
   flatness of better than +/- 100 microns on average.  The flatness
   went out of spec where there were imperfections in the kapton
   surface and along the g10/kapton edge due to the difference in
   thickness of the materials.
 - Brian has been told that our dummy cathode boards with copper
   strips are being held up as the board manufacturer cannot get
   the material quickly.  As soon as it arrives at the manufacturer,
   the turn-around time will only be several days before delivery
   to us.
 - Brian will make another mechanical mock-up with these new boards
   (using the lessons learned from the first prototype) to understand
   what issues the copper strips bring about in the manufacture.
 - Brian has been asked to make a cathode plane using the tensioning
   system and to measure the surface to quantify the lateral distortions
   of the cathode strips.  The details on what the set tension should
   be are still unclear.  At the present moment, this is more of a
   visual and "feel" process.

3). Circuit Board Material:

 - Our current planning for the STB and HVTB circuit boards is the
   standard FR-4.  However DSC brought up another board material
   called HVPF that Chris Cuevas was talking about for Hall B.  This
   material has a much higher dielectric constant than FR-4 and issues
   with spacing of traces, thickness of layers, leakage currents, etc
   are much less of an issue.  This material also has a much higher
   surface resistivity than FR-4.
 - Fernando will follow up with Chris on this material.  The big
   issue here is the rumored cost of this material.  It is not
   expected to be cheap.

4). Ground Plane Thickness:

 - Gerard Visser was given a sample of the aluminized mylar that we
   nominally plan on using for our ground planes and he was going
   to give us feedback on the suitability of this material.  No
   word yet.
 - After the meeting, DSC sent Gerard email to ask him to weigh in
   on this issue.

5). Design Issues:

 - We have been discussing at our last two meetings a current issue
   with the design regarding the space available for the daughter 
   board and connector on the cathode plane face that is closest to 
   the anode board.  Presently there is no straightforward way to fit 
   these connectors in without trimming down the g10 spacer or adding 
   clearance notches to the anode board (which leads to flexing of
   the now weakened board).
 - Fernando believes that he has located some slimmer profile connectors
   that are below 5 mm thick.  This should help.
 - We also discussed an option of putting the connectors for the
   cathodes on the back side of the cathodes.  In other words, the
   connectors could fit in the middle of the cathode sandwich.  This
   would save us from having to notch the anode boards.  After working
   out the basic ideas, this seemed to be a promising avenue.  DSC
   asked Tim to prepare some drawings/sketches of what we had talked
   about and we will continue down this design road discussion at
   our next meeting.

6). Cable Layout:

 - Joe B. did not attend the meeting this week so we could not
   discuss the latest drawings on the cable layout.
 - DSC actually put the wrong idea in last week's meeting minutes.
   The readout cables will indeed go all the way around the FDC
   package.  However the daughter board connectors will be fixed to
   be on the FDC perimeter above the rails so that they are
   accessible.

7). Engineering Work:

 - Tim has done a number of calculations of stress and thermal environment.
   After the meeting, Tim passed along what he had to DSC.

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