Minutes 4-4-2007

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FDC Weekly Meeting

Date: April 4, 2007

Participants: Daniel, Tim, Kim, Simon, Brian

Next Meeting: Wednesday, April 11, 2007 @ 1:30 p.m.

FDC Budget

 - The FDC budget preparations for CD-2 are nearly complete.  We are
   waiting for just a few last numbers.  These include the quotes for
   the composite frames for the cathodes and the storage boxes for the
   wire planes.  
 - When these numbers are available in the next few days, DSC will turn
   over our budget document, the manpower request for construction, and
   all backup information (quotes, pricing information, etc) to Elke.
   Note the FDC budget document is on the GlueX portal as GlueX-doc-735.

Short Term Work Plans

 - DSC has produced a document listing all short term (i.e. this year)
   FDC work plans and distributed copies of this draft.  Everyone should
   look this over and provide feedback as to items that have been
 - Once we have a complete document (for now anyway), it will be posted
   on the FDC web site (http://www.jlab.org/Hall-D/detector/fdc/ for those
   who are not aware of this).

Cathode Sandwich Construction

 - Brian has been working on producing new cathodes with the dummy
   cathode boards that just arrived.  The latest version will be one
   without the Rohacell backing.  He will make a single cathode frame
   and deliver it to the JLab Survey folks to test non-contact flatness
   measurement schemes using an optical system.  His first step was
   to glue the 3 separate cathode boards together.  The different strips
   have built-in fiducial/alignment marks to reduce the positioning
   uncertainty to a few mils.
 - Brian has been in contact with the board vendor regarding the defects
   that are apparent in these boards to see how we can eliminate them
   from our production planes.  He has not gotten any feedback yet,
   although they are apparently aware of the problems.
 - Roger has been working to find a vendor who can supply the cathode
   board material in a size suitable to manufacture a single piece
   cathode board (remember it is the material that is the present
   limitation as the board manufacturer can handle the full-size boards).
   He has not had any luck as of yet, but feels confident that there is
   some company out there that can deliver.  Presently he has 3 contacts
   that he is pursuing.  The company needs to be able to provide boards
   on a 1 or 2 mil kapton backing with copper thicknesses down to
   1 micron.
 - Tim is currently working on developing a test plan to measure the
   board deflection.  There is still much to think about, but remember
   the goal is to calculate the expected cathode deflection in the
   electric field so that we can work to keep this below a level that
   would impact the cathode resolution.  These deflection calculations
   need some numbers from measurements to determine the tension.  More
   to come.
 - Before the new cathode boards are tensioned, we will measure the
   strip positioning so that we can have a reference to compare against
   after the tensioning.  We need to understand what we are up against
   in terms of lateral cathode surface distortions.  We then need to
   define a tolerance and then a procedure for reproducibility for the
   production boards.
 - A major concern with the no-Rohacell backing option for the cathodes
   is the deflection of the surfaces in the electric field produced by
   the wires.  We need to study the deflection also as a function of
   the kapton thickness.  If we use 1 micron Copper and eliminate the
   Rohacell, we could potentially afford to go with a thicker kapton
   backing to reduce the effects.  Remember that we need to keep the
   tension on the cathode boards to a minimum to prevent distortions of
   the strips.  We also discussed employing a Rohacell web behind the
   cathode that we could attach to.  More to come on this issue.

Circuit Boards

 - As Roger is on a chase (or a mission) to find a way to enable us to 
   construct the cathode boards from a single piece, DSC also asked him
   to find a company that can produce our STBs and HVTBs as a single
   piece.  This will simply the wire frame construction and will give
   us more flexibility in laying out the connectors on the STB side and
   more flexibility in laying out the HV busses on the HVTB side.
 - Kim has begun work on a layout of the HVTB boards.  She began working
   on a single board first.  The capacitors will again be located on the
   back of the boards.
 - We discussed the possibility of including cut-outs on the G10 frame
   to enable access to the capacitors on the STBs and HVTBs.  This was
   viewed as a good idea that we should pursue.

Frames and Spacers

 - We have a design for a composite cathode frame to replace the
   current 5-mm thick G10 frames in the current design.  We have
   decided that these frames will represent our nominal design choice.
   The design of these frames (also 5-mm thick) has an outer surface
   layer of e-glass (non-conductive), a layer of carbon fiber, and an
   inner Rohacell foam layer.  The thickness of these frames is effectively
   a factor of 3 or 4 smaller than the G10 frames.
 - Simon will pass the dimensions and material properties on to Richard,
   David, and Eugene for Monte Carlo studies of photon conversions.
 - We discussed replacing the CH2 spacers with the composite design,
   but the savings in terms of thickness is modest (less than 20%).  Given
   how much easier it is to work with CH2, we have decided to keep this
   as our nominal material choice for now.  Given that the costs for
   the composite and the CH2 are about the same, we can change our minds
   downstream if necessary.

Gas Ports

 - Casey in the JLab machine shop developed a much simpler gas port
   than we had initially planned.  He developed a nice gas port by
   crushing a piece of stainless steel tubing.  The shaping of this
   tube still needs some fine tuning to give us the flared shape that
   we are after for better gas distribution.  These ports can be
   inserted into the CH2 spacer or the G10 wire support frame.  We
   have yet to make a decision.

Magnetic Field Studies

 - The folks at BNL have gotten back in touch with us regarding a
   possible magnetic that we could use.  However they have to check
   the field orientation.  It appears that there may have been some
   confusion in what we told them.  Brian will follow up on this.
 - Brian also gave the information on our magnet requirements to Elke
   so that she could communicate with her contacts at DESY.  No word
 - We discussed the options that may be available.  At BNL (which is
   much closer and more convenient to get our equipment to), we would
   be doing field tests with cosmic rays.  At DESY, we would have the
   opportunity to do the field tests in a beam.  It is not clear if
   we want to do both studies simultaneously.  We need to think about
   this in some detail.

Small-Scale Prototype Work

 - Roger is working to finish the layout of the new +/-75 deg cathode
   boards for the small-scale prototype.  He expecting to complete this
   work in a few more days.  He will circulate the drawings upon completion
   so that we can get these out the door soon.

Ground Planes

 - A minor complication has come up with the ground planes that go
   between each cathode layer if we do not use the Rohacell backing.
   How do we support them?  Our goal is to define the ground plane so
   that it is equi-distant between the cathodes.  We need to think about
   this issue and how close the ground planes can be to the cathodes
   and still do the job.  This is a question for Fernando and for Gerard.


 - The first draft MOU provided to Karen Kephart has been modified by
   DSC and sent back to her.  DSC will follow up with Karen to find out
   the status of the draft.  We want to get this to our procurement folks
   real soon to get the formal process underway to complete the agreement
   so that winding of test planes can proceed this summer.


 - Simon will give a talk on his GARFIELD studies of various gas
   mixture options for the FDC system at the next Hall D meeting.

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