Notes Meeting Wed Jan 28 / tagger

[Elton Smith <elton@jlab.org>]

Hall D Meeting Wed Jan 28 / tagger
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Guangliang Yang arrived over the weekend, but due to the snow storm and 
the lab closing, meetings with Ravi and Paul could not be scheduled till 
Tuesday. Guangliang met with Ravi and Paul yesterday and reviewed the 
drawings that Jim produced and sent around for comments.

This is a new concept based on the magnet being completely inside a large 
tube which is evacuated. The tube itself is approximately 7 m long, the 
tube is 2 m in diameter. The vacuum would be connected directly to the 
accelerator through various apertures. The suggested vacuum for this 
region is 10^-4 torr (Hall B is at about 10^-5). The pipe would consist of 
approximately 270 degrees of round pipe. The remaining section would 
consist of two flat sides: one to support the magnet and the other 
parallel to the focal plane detectors.

The magnet is 90 tons (6m x 1.5m)

Questions raised included the cost of pumps and speed with which they can 
pump down the system. Beneath the large tube would be attached a smaller 
but longer (11 m total) vacuum chamber with an exit window which would be 
close to the tagging focal plane.

Access to the water and electrical connections on the magnet would be 
provided through the upstream flange which is a cap to the tube. However 
it would require breaking vacuum for any maintenance and reestablinshing 
adequate vacuum afterwards. This activity must be able to be accomplished 
on a reasonable time scale.

Access to the magnet and coils would be by detaching the 270 degree round 
side which is under vacuum through a o-ring seal. Presumably this would 
happen very infrequently and in the current civil design perhaps require 
removal of the roof on the tagger building. 

This design raises many questions especially related to breaking and
reestablishing vacuum, and maintaining vacuum at the required level. First
the the level (10^-4 torr) should be reviewed as it may drive many other
decisions. Also, maintaining a vacuum region which is in contact with
coils may be an issue as they may trap gas and/or outgas. Finally the cost
of pumps of the necessary size to establish vacuum in a relatively short
time needs to be determined.

Ravi is putting some of these concepts into electronic drawings which can
be used for further discussion. He will continue working with Guangliang
till tomorrow when we will review where we are and see if there are any 
more issues which can be addressed during this visit. These considerations
can serve as a basis for further discussions by the collaboration.

Cheers, Elton.


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