Changes to FDC XML definition

[Simon Taylor <staylor@jlab.org>]

Hello, everyone.

I've made several significant changes to the XML definition for the FDC 
to make the description conform
better to the current engineering drawings.   A svn log message 
describing the changes is appended below.    I have also moved the FDCs 
closer to the CDC (for this you will need an updated version of the 
main_HDDS.xml file).   In order to use the new geometry you will have to 
update hitFDC.c  in programs/Simulation/HDGeant and the 
lorentz_deflections file in calib/FDC.   Note that the 
lorentz_deflections file is consistent with the new position of the FDC 
with respect to the CDC and is not guaranteed to give sensible results 
for significant changes in the position of the packages.

Some parameters, such as the actual distance between the cdc and the fdc 
and the package-to-package spacing still need to be optimized.

Simon
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r5183 | staylor | 2009-05-15 15:08:42 -0400 (Fri, 15 May 2009) | 1 line

First version of new geometry for the FDC.  The chambers are no longer 
grouped in modules of three; the new unit is a single chamber, so in 
principle all of the rotation angles of the chambers for a package can 
be different or a chamber could be removed from a package.  The wire 
plane-to-wire plane separation within a packages was reduced from 3cm to 
2cm.  The 2mm foam in the active area has been removed and the thickness 
of the ground plane has been reduced.  The package-to-package support 
shell has been changed from aluminum to FR-4 and the support rods are 
now also FR4.  The compression rods are now Ultem-2300 and gusset rings 
for the compression of the o-rings have been added.  A ring for 
supporting the cables on the upstream side of the FDC has been added.  
The spacer ring between the wire plane and one of the cathode planes in 
a chamber is now polypropylene instead of a composite.  The other 
support structures are now more consistent with the current engineering 
design.  The chamber gas now fills the entire interior package volume 
instead of just the 1 cm active region of each chamber.  The epoxy in 
the cathode material has been removed from the active region.
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