[Halld-tracking-hw] CDC endplates, feedthrus etc (fwd)

[Eugene Chudakov]

Tim suggests to use 6mm aluminum instead of 6mm carbon fiber
composite material for the downstream endplate of the CDC.
We made an estimate of the thicknesses involved:

a) The inserts (donuts, feedthroughs, pins etc.): 3.6% RL
b) The composite endplate (the holes make about 30% of the surface): 1.9%
b) The Al endplate with holes: 4.7%

Changing the plate to Al will add 2.8% of RL,
which is an additional loss of 11% of events with 4-photons passing the plate,
and a 20% increase of the scattering angle of charged particles in the plate.
It does not sound dramatic, unless there are many similar compromises
in storage.

------------------------------------------------------
Eugene Chudakov
http://www.jlab.org/~gen
phone (757) 269 5352  fax (757) 269 5703
Thomas Jefferson National Accelerator Facility
12000 Jefferson Ave, Suite #4
Newport News, VA 23606 USA

---------- Forwarded message ----------
Date: Fri, 31 Jul 2009 11:24:12 -0400
From: Tim Whitlatch <whitey at jlab.org>
To: Curtis A. Meyer <cmeyer at ernest.phys.cmu.edu>
Cc: Beni Zihlmann <zihlmann at jlab.org>, Eugene Chudakov <gen at jlab.org>,
     Vladislav Razmyslovich <vgr at jlab.org>, Gary Wilkin <wilkin at andrew.cmu.edu>
Subject: CDC endplates, feedthrus etc

Hi Curtis,

After working with several vendors on the manufacturing of these parts, I offer 
the following information and suggestions;

1. Endplate stereo angles position tolerances should be opened up. The stereo 
holes .positional tolerance between  005 and .010 in. may be possible. A change 
in temperature between machining and measuring of 4°F will cause a change of 
.0025 in. on the outermost holes.

Recommendation: Stereo hole positions be opened up to .007, straight holes to 
.005. The positions of the crimp pins can be determined as installed by 
photogrammetry or CMM. (within .002)

2. Downstream endplate of carbon/epoxy composite will need to be custom made. 
The thickness tolerance will be ± .009 inches (± .005 for alum. plate). The 
plate is .236 inches thick. If we make it thicker and machine it, there is a 
chance for warpage. The cost is about $15K additional for the composite and the 
results are questionable.

Recommendation: Make downstream plate out of .25 in.aluminum. The density of 
the carbon epoxy is about 60% of aluminum. The 3600 holes in the endplate 
remove about 1/2 of the material. The feedthrus donuts and inserts dominate the 
mass in the area..

3. The plastic feedthrus can be injection molded for about half the price of 
the machined parts ($113K in savings). They can be injection molded if the 
diametral tolerances are opened to .002 to .003 inches. The aluminum parts 
would also be cheaper with looser tolerances (.001 in).

Recommendation: Open up tolerance on components as stated above.

Slava has updated the drawings showing many of these options. please see them 
at:

http://www.jlab.org/~vgr/CDC%20Updated%20Drawings-7-30-2009/

Please consider these changes and let me know what you think.

Thanks,

       Tim