Minutes 3-21-2007

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FDC Weekly Meeting

Date: March 21, 2007

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

Next Meeting: Wednesday, March 28, 2007 @ 1:30 p.m.

Magnetic Field Issues

 - We have heard back from Andrey Korytov from CMS who is one of their
   cathode chamber experts.  He invited us to set up a phone conference
   with him to discuss the magnetic field issues.  Simon will arrange
   to set this up in the next few weeks.  Daniel will prepare a list of
   talking points and circulate it for comment.
 - Simon is working on preparing a list of gas mixtures used by various
   collaborations in their cathode chambers.  He will then perform
   GARFIELD studies to plot the Lorentz angle as a function of cell
   position (equalizing the gas gains) so that we can come to some
   understanding of what are some candidate gas mixtures that we can
   consider.  He will also study how the cell size affects the Lorentz
   angle.  We need to also understand the impact of the time to distance
   relation on the gas choice (linearity, effective drift velocity) and
   we also need to consider chamber life time and performance issues
   with the different mixtures.  Daniel has some articles on this that can
   be used for reference.
 - Brian has sent out several inquiries to folks at BNL and SLAC to
   find out about availability of suitable magnets with which to perform
   our B-field studies.  He will also provide the information to Elke
   as their may be contacts in Germany that she can follow up on.
 - Simon and Daniel will work to develop a test plan for these studies 
   and circulate for comments.

Material in the Active Area

 - We are currently investigating ways in which to reduce the material
   in our active area.  One plan is to remove the Rohacell backing
   from the cathodes.  This would reduce the thickness in the active
   area by roughly 1/3.  Simon will perform deflection calculations on
   the surface of the cathode (as a function of tension) so that we
   can understand how the electrostatic forces affect the surface.  Once
   these are completed, Simon will perform calculations of the variation
   with gain across the FDC package from the edge (where the deflections
   are minimal) to the center (where the deflections are maximal).
 - We are also pursuing ideas to reduce the cathode trace thickness 
   below 1/7 oz of Cu.  Brian is contacting companies to find out what
   they can provide.  1/7 oz of Cu amounts to roughly 5 microns of Cu.
   Brian is looking into manufacture of cathode planes with thicknesses
   down to 1 micron of Cu.  Fernando will think about a bench tests that
   can be performed to test the electrical properties of the cathodes
   to understand if there are any performance issues.  He stated that
   he is more concerned about mechanical limitations.  Namely that with
   very thin copper layers we will not be able to reliably solder to
   the surface (although gold-plating may be an option around this) and
   he also stated that with very thin Cu layers, vias are typically not 
 - Brian is also contacting manufacturers to find out about aluminum
   conductors on these circuit boards.  This cannot be handled within the
   PCB industry, and he is working to contact folks who can sputter on
   thin aluminum layers through a mask.
 - Roger has been doing some digging trying to find companies that can
   provide stock for our cathode boards that will allow us to manufacture
   our full-scale cathode as a single board.  Note that the issue is not
   with the PCB manufacturer, but with coming up with the stock.  Roger
   has had no luck in finding any companies, but he is still pursing
   some leads.
 - We will set a design goal of material in the active area of 1 to 1.5%
   of a radiation length for all 4 FDC packages.  Starting from this,
   Simon will do some calculations to find what the associated copper
   thickness is.  This will be our upper limit on Cu thickness that we
   can use as a basis for the design.

FDC Design

 - Given the goal to reduce the material thickness in the active layer
   to 1 - 1.5% of a R.L., we are working on several aspects of the
   FDC package design.  We are still assuming a nominal design with the
   preamp daughter boards connected to the frames.  For the design we
   should assume that the connector thickness is 4.2 mm, so we need to
   design the system for clearances of 4.3 mm.  The current thinking is
   that the wire plane connectors on the STB will be mounted to the
   face of the STB.  For the cathodes, we want a design with all of the
   connectors on the back side of the cathode boards.  So the daughter
   board connectors for the cathodes will reside in the middle of the
   cathode sandwich.  Note that this will increase the layer to layer
   gap within a package by a few mm to accommodate this.  This is not
   viewed as an issue.
 - Tim will work to produce a sketch of this layout so that we can
   understand the clearance issues for both the cathodes and the anodes.
   We will discuss this at our next meeting.
 - Fernando is continuing to contact connector manufacturers to find
   out what options are available for even thinner connectors.
 - Note that we have decided that our nominal half-gap should be 5 mm
   as the smaller the cell size the smaller the magnetic field affects.
   It may even be that we will have to plan for half-gaps below 5 mm,
   so we need to be prepared.
 - The issue with getting the cathode signals out from the back side
   of the cathodes is a bit of a tricky issue.  Fernando will think about
   this and provide us with some options at our next meeting.
 - Our new nominal design for the cathodes is that the stereo angle will
   be +/- 75 deg with respect to the wires.  Chuck will provide some
   CAD drawings so that we can understand the placement and clearance
   issues that we will be faced with.
 - The strip pitch will be a constant across the cathode surface.  This
   pitch will be the same as the half-gap.  However to minimize the rates
   on the hottest strips near the beam hole, we will most likely remove
   the conductor from the beam hole area and readout half strips on
   opposite sides of the circuit board.  Note that the highest rate
   cathodes are presently in the last package.  To combat this we have
   nominally decided to employ an increasing deadened area in the FDCs
   as we move from the upstream to the downstream package.  David 
   Lawrence will provide this size.  This would amount to a 7-cm diameter
   deadened area for the most upstream package increasing to something
   like 10-cm for the most downstream package.  This will likely reduce
   the occupancies to an acceptable level without having to cut the
   central strips in half.

Cathode Frame Design

 - Tim has produced a drawing of a new sandwich design to replace the
   5-mm thick (10-cm radial thick) G10 cathode frames.  This sandwich
   would be constructed from thin graphite skins, with fiberglass and
   Rohacell on the inside.  This would reduce the effective radial
   thickness of these pieces by a factor of 3 to 4.  This is important
   to reduce the photon conversions in the FDC frames and the preshowering
   thickness.  We are still nominally planning to employ G10 for the
   wire frames (necessary for rigidity) and CH2 for the spacers.
 - Simon will do some calculations of the effect of the new design from
   Tim on the thickness.
 - We need to contact Eugene to study the effect on his simulation
   results with the new design.

Low Voltage System

 - Daniel had estimated that we should employ a single 30-A supply for each
   FDC package.  Fernando has indicated that this may not be sufficient.
   His calculations indicated that we should employ 50 or 70A supplies
   for each package.  We need to converge on this and make a decision so
   that we can update the budget appropriately.
 - Joe needs information on the LV granularity and fusing specs so that
   he can make some decisions on cable choices.

Small-Scale Prototype Plans

 - Roger will complete the design of the new cathodes with the +/-75
   deg stereo angle as well as the associated frames.  These should
   be ready so that we can write the PR in about 3 weeks.  Roger
   indicated that this should not be a problem.  We will need to
   review the drawings to check for conflicts before they go out
   the door.
 - The 90 deg. stereo angle cathodes are available, however we cannot
   use both in the chamber as we cannot quantify the resolution without
   defining an external track (which we cannot yet do).  However Daniel
   suggested to use one 90 deg plane and one 45 deg plane to do some
   intermediate studies.  Simon will do some calculations to check
   what we can expect in terms of resolution.
 - Summer student: Simon and Daniel have completed the project definition
   for a summer student and have passed this on to Elke.  The project
   would be to calibrate the scintillator hodoscope and the cosmic
   ray chambers in our test setup.

FDC Budget

 - Daniel circulated a request for budget items for the FDC to Tim,
   Brian, Fernando, and Joe.  These are needed ASAP as Elke needs
   the budgets by early next week.  Things are starting to trickle in,
   and folks should contact Daniel if they have any questions on what
   to provide.


 - Daniel has prepared a draft of the FNAL MOU for stringing the FDC
   wire planes based on an example provided by Mike Syptak.  Brian
   and Simon need to provide feedback.  We will then distribute the
   draft to Elke, Elton, and Karen Kephart for feedback.  The next
   step is to turn this over to Mike Syptak and the procurement folks
   here at JLab.
 - Note that our plans are to wind several test planes this summer so
   that we can finalize the specs and the winding technique.

Dummy Cathode Planes

 - The dummy cathode planes are set to arrive at JLab next week.
   Simon will perform strip-to-strip capacitance measurements on them.
   He will also contact Gerard to find out if there is anything else
   useful that we could measure.  Joe will provide a unit to perform
   the measurements.
 - Brian will then begin construction of a second Rohacell-backed
   sandwich and a full sandwich without the backing so that we can
   understand the distortion issues and the cathode construction
   issues in this alternative design.
 - Brian will follow up the JLab Survey Group about the flatness
   measurements (non-contact) of the new cathode planes.  We need
   this ready in about 3 weeks or so.

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