FDC Material and Noise Rates

["Daniel S. Carman" <carman@jlab.org>]

Richard, Matt, David, et al.,

I have seen some of the rate studies that have recently come out.  As
I do not know what you are planning or what you have completed fully,
I thought that I would send a follow up email on what we need to push
forward with the FDC design and to complete the documentation needed
for CD2 to address the questions raised by the DC review.  The questions 
that we need to address have to do with 1). material in the active area 
and 2). material in the inactive area of the FDCs.

Questions on material in the active area:
-----------------------------------------
To simplify the situation, I would like to know what the rates are
per cathode strip and per anode wire for all planes in the FDC system
for the two options that we are pursuing.

Option 1: 5-mm Rohacell backing with 10-cm diameter hole cut about the
          beam line.  1 mil kapton + 2 micron copper strips for the
          cathode planes.  In this option the copper strips about the
          10-cm diameter hole are split in two and the hole in the
          cathode board matches the hole in the Rohacell backing (i.e.
          the strips and kapton do not go through the beam line hole).

Option 2: Same as option 1 but with the Rohacell removed.

The relevant gas mixture is 40/60 argon-CO2.  Note that we are also
starting to consider a design to replace the Rohacell backing with a
composite foam that should be significantly less material that a solid
Rohacell piece.  However, with the results for the two options, we at
least have set reasonable upper and lower limits for the rates that
hopefully can serve to help us set a design spec.  We will also need
MC run for both cases to show momentum resolution vs. p and theta.

Questions on material in the inactive area:
-------------------------------------------
We would like the photon conversion studies that were presented about
a month ago repeated for the FDC design where the 5-mm thick cathode
frames are replaced by the 5-mm thick composite carbon-fiber/Rohacell
frames.  We are also considering replacing the CH2 spacers with a
composite frame, but this should be considered in a separate study
as it is not part of our nominal design.  Again, the goal is to use
these studies to set a design spec.  So we all need to think about
what photon conversion rate in the frames and cables is allowable.


Let me know if you have any questions.  


			    Regards,

				Daniel


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* Dr. Daniel S. Carman                   e-mail : carman@jlab.org    *  
* Staff Scientist                        office : (757)-269-5586     *
* Jefferson Laboratory                   web: www.jlab.org/~carman   *  
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