Comments on new Tagger magnet vacuum tank

[Elton Smith <elton@jlab.org>]

Comments/thoughts on the new tagger vacuum tank design
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I do not have much experience with the tagger designs, so some of these 
off-the-top-of-my-head comments are probably obvious to those that have 
been thinking about this. I also spoke briefly with Dave Kashy about the 
tagger design with external vacuum chamber to get his thoughts on this. 
Here are some observations.

Turbo pumps could be about $30K, not excessive compared to magnet cost of
about $1.5 M. Vacuum is 10^-5, compared to 10^-5 in beam line and 10^-6
around target.  Time for initial pumpdown is hours, 10-12 hours to steady
state vacuum.

- All cooling water (LCW), and power for magnet must be in vacuum, 
requiring corresponding feedthroughs.
- All instrumentation on magnet would need feedthroughs into vacuum 
system.
- Any water leaks would contaminate the vacuum space.
--> Maintenance issues need to be addressed

Current Hall B design uses the rigidity of the magnet itself to support 
the vacuum chamber. The vacuum chamber tank design requires external 
strengthening.

Pressure on vacuum chamber is approximately for 1m x 7m = 40in x 
280in=11,000 in2 x 14.2 lb/in2 = 0.3 x10^6 lbs = 150 tons, or comparable 
to weight of magnet.

Volume evacuated is large compared to what is actually required for 
physics.

We discussed several of these issues with Ravi, Guangliang, and Elliott. 
Ravi has entered many of the hand drawings into the computer and will make 
drawings available on the web as pdf files for discussion. 



-- 
Elton Smith
Jefferson Lab
elton@jlab.org
(757) 269-7625