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FDC Weekly Meeting

Date: December 3, 2009

Participants: Daniel, Mark I., Brian, Fernando, Tim, Kim, Chuck, Bill, Casey, Simon, Eugene, Glenn

Next Meeting: December 10, 2009 @ 1:30 a.m.

General Construction Updates

 - We identified several big leaks in the first of our cathode sandwiches. 
   It is suspected that they arose from uneven clamping pressure during the
   sandwich lamination. Casey mounted the cathode to the granite table
   vertically after we disassembled the stack and went around and epoxied
   the gap more thoroughly. This same operation will have to be completed
   on the second cathode sandwich as well.
 - During the step of epoxy sealing of the first cathode sandwich, epoxy
   inadvertently filled one of the rigid-flex power connectors. This was not
   found until after the epoxy cured. The rigid-flex assembly was broken
   off and replaced.
 - The through-holes on all stack layers used for the first two layers were
   re-epoxied. This time pressure was applied so that the epoxy got
   deeper into the Rohacell. One issue is that during stack assembly, the
   threaded rods that go through the holes were removing epoxy, which led
   to potential leak paths.
 - Given that Bill was not satisfied with the gusset arcs that he made out
   of plastic, he had a new beefy aluminum set made in the shop to replace
 - Immediately after the FDC meeting, we reassembled the two layers of the
   stack for leak checking, as well as HV testing and signal checkout on the 
   second layer wire board and cathodes. During assembly, we noted that
   the o-rings in one of our spacer rings were compressed and were below
   the surface level of the spacer. We replaced these o-rings (which were
   made from the 50 durometer material) with the soft o-rings (made from
   the 8 durometer material) mounted on top of pinstriping tape to raise
   these level by about 8 mils in the o-ring groove. Leak checking will
   proceed this week. 
 - Before adding the third (and final) layer to the full-scale prototype,
   we will do signal checkout. We will hopefully have a leak-tight chamber
   and can let gas flow over the weekend to purge the two layers. Stay
 - Fernando completed his test plan on the single layer prototype using 
   a single anode preamp board and a single cathode preamp board, both 
   stuffed with the new GAS-II preamps. He has posted GlueX-doc-1384
   that folks should take a look at. These few plots have taken us a long
   time to acquire and the news is quite encouraging as a first series of
   measurements. Obviously, there is much more to come to finalize and
   checkout the FDC system design.
 - Brian prepared the wire samples from the CDC/FDC wire spools that arrived.
   They were delivered to the W&M folks who will be doing the check out.
   They have already been provided with samples of our sense and field wire
   to set up their machines to carry out the planned measurements. The test
   procedures for wire spool acceptance have been prepared by Bill and are
   on the FDC web page.
 - Bill will follow up on getting us access to an oxygen sensor to check
   the oxygen levels in our chamber outflow.
 - The preliminary FDC stack assembly document draft is located at:
   /u/group/halld/Engineering/PRELIMINARY DOCUMENTS. The document will 
   continue to be fleshed out during the assembly procedure for the 
   full-scale prototype. We will have to add steps in our construction plans 
   for leak checking.
 - DSC pushed for better tracking of our epoxy freshness. We need to check
   the dates on the epoxy before using. If it is too old, then the epoxy
   needs to be discarded so that it is not used in the construction.

Wire Frame Update

 - Wire frame P3 needs to have its final preparations completed. This
   includes electrical QA/repairs, final cleaning, HV components potted in 
   Humaseal, recheck of epoxy seals. It then needs to be laminated to its
   cathode. We hope that this work will proceed on Monday so that the frame
   is ready for stack assembly on Tuesday. Stay tuned.
 - We need to have a dedicated meeting to design what the schedule for
   work on the Phase 3 wire winding will be. The highest priority for
   work scheduling will be doing work on upgrades of the wire winding
   facility. This includes a better strongback design, the design and
   construction of precision combs, modification to the wire winding
   table, and a list of other items with the system. Stay tuned, more
   to come.
 - DSC received a message from Keith Solberg at IUCF regarding the status
   at IUCF. They are in the midst of a management shake-up. It is time to
   schedule a meeting of a more formal nature so that firm committments
   can be made. DSC will set a meeting up.
 - The wire frame construction document is located at:
   /u/group/halld/Engineering/PRELIMINARY DOCUMENTS. We will include
   the information on the wire electroplating process shortly.
 - The parts of the jig to use for the wire electroplating operation
   are in our hands. They will be assembled as we find time.
 - We need to prepare a document for the electrical QA of the preamp
   connectors on the wire boards.
 - DSC, Bill, and Fernando will plan a meeting to go over the circuit
   board design work for Kim.
 - Kim is following up with the contacts obtained from Peter Monaghan 
   regarding large-area PCBs. Kim is still in back and forth with the
   board house and the board material supplier. The outlook may be rosier
   than it was a few years ago. Stay tuned.

Cathode Update

 - Soldering of all rigid-flex assemblies for the full-scale prototype
   has been completed.
 - The current draft of the cathode construction document is located at:
   /u/group/halld/Engineering/PRELIMINARY DOCUMENTS.
 - We need to prepare a document for QA/stuffing/cleaning for the cathode 
   boards and a similar document for the cathode daughter boards and ground 
 - The order for the cathode material was scheduled to arrive on Dec. 26.
   Roger asked that it be held for delivery until the first week of January
   when shipping and receiving is open for business. Tim suggested that 
   before we store away the board material, that we do an inspection and
   quick QA check to be sure that there are no obvious problems before we
   store the material away.

Leak Issues

 - The second half of the meeting was focussed on the leak issues that have
   been plaguing us during stack assembly so far. DSC began by listing some
   of the known issues:
    * Leaks in middle of cathode sandwich due to uneven clamping pressure.
    * Leaks through the via on the wire frame PCBs. This can be solved by
      having board house fill the vias and then to cover all with solder mask.
    * Better sealing of the I.D. of the wire frames.
    * Defining the torque applied to the stack bolts so that we don't
      over-tighten and crush the Rohacell.
    * Better sealing of the through holes on all layer frames.
    * Modify the PCB design so that no traces are directly under the o-ring.
    * Modify the spacer groove design to allow us to eliminate using the
      instant adhesive to hold the o-rings in place.
    * With the design problem with the capacitor position on the back side
      of the STB, there is no support under the o-ring, i.e. the 
      unsupported circuit board is to flexible to push up against the o-ring
      for a reliable seal. This will not be present with the final circuit
      board design.
  - Bill presented a much more aggressive design replacing the gas spacer
    and inner cathode frames with solid G10. His design incorporates a
    wide gasket seal.
    * Fernando had a few concerns with potential gas leaks from the foam
      gaskets. He suggested getting more information such as:
         a. material composition  
         b. outgassing
         c. adhesive
         d. long term performance with Ar-CO2
         e. radiation "hardness".
      Most foam gaskets and contact adhesives loose their properties over 
      time. In particular, most foam gaskets loose their elasticity and 
      crumble, even with closed cell compositions. He is concerned that 
      after 2 years of operation leaks will develop.
    * Obviously the amount of material he is proposing adding back in is
      of concern. Bill will provide a listing of the parts n' pieces to
      Simon for his proposed design and we can check the background issues
      and photon losses for BCAL and FCAL. 
    * DSC raised concerns about straying too far from the nominal design as
      we will not be able to full vet and study the ideas within the 
      full-scale prototype. There are lots of tight spaces and potential
      conflicts can be (and have been) missed just relying on our 3D CAD
    * Bill is concerned about the crushing of the Rohacell. We discussed
      the notion of using inserts in through holes on the frames.
    * Tim's notes from the discussion:
        1. Causes and potential fixes for the production  packages were discussed
        2. Some known and Possible causes of leaks include leaks through the 
           Rohacell bonding boudaries, deflection of unsupported wireplane PC board 
           under o-ring, grounding vias on pc board, bond voids on cathode 
           sandwich, protrusion of traces (3-4 mils) on pc board, not enough 
           compression on o-ring, too much compression on Rohacell, not enough  
           stiffness in outer channel supports.
        Action items:
       a. Develop test plan for testing existing design, slightly changed 
          design and addition of G10 ring to support bolts and gas seal (Bill 
       b. Get worst case additional material to Simon for background analysis  
          (Bill Crahen)
       c. Perform background analysis on increased material (Indiana U?)
       d. Gather all changes needed for production pc board (Kim Shinault).
    * Obviously lots of ideas and discussion that question the nominal
      design at this late stage made folks nervous and edgy. More discussion
      and planning will continue as we move forward.

Preamplifier Boards

 - An order for more ASIC chips is expected very shortly. Fernando expects
   that we will have ~40 boards ready by the end of November.

Cosmic Ray Test Stand

 - Several meetings ago we focussed on the wiggles seen in the reconstructed 
   wire position from the cathodes (see log entry 419) in the
   FDC logbook. We believe that the periodicity seen is due to the algorithm
   Beni is using to determine the U and V centroids. Beni get back to this
   soon. Stay tuned.

Work List

 - The FDC short-term work list has been posted on the FDC web site.  
   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.