Permanent magnets for Hall D

[Elliott Wolin <wolin@jlab.org>]

Hi,

I talked with Steve Benson from the Acc. division about permanent magnets.  He
designed the permanent magnet wigglers for the FEL.

For the discussion I assumed a 12 gev beam, 4 m magnet, and 5 degree bend (3.5
degrees actually might be enough), giving a B field of a bit less than 1 Tesla. 
I assumed we'd need a magnetized region of approx. 2 cm by 5 cm.  For us
precision is not critical, although it is for wigglers.

Steve said that such a magnet was no big deal, similar magnets are being used at
Fermilab.  We could probably use their design.  He noted that we'd need
radiation resistant magnetic materials, e.g. Sm-Co (Samarium-Cobalt)...we can't
use AlNiCo or other cheaper materials as they'll eventually lose their
magnetization.

He estimates a magnet cost of around $100K - $200K, and a few months lead time. 
There are a number of possible vendors.

Note that the difference between the above ground and below ground options is
around $500K. The permanent magnets probably wouldn't be needed for the below
ground option, so the difference in cost is decreased to around $300K.  There
may be other costs for the below ground option we haven't accounted for yet,
though...


				Sincerely,
					Elliott
 

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