[Halld-cal] FCAL pmt mag shield

[Tim Whitlatch]

Hi Matt,

Attached is a spreadsheet showing the magnetic field inside the short 
shield with .014 in mu metal . The ID of the steel pipe is 1.5 in.. The 
mu metal is 1.35 inched ID (need to ensure this clears all the pmts). 
The space between the mu metal and steel was filled with mylar sheets 
(approx. .06 in thk). It shows that there is a threshold just under 200G 
that the shield works (ie below 0.5G). At 185G the shield performs as 
desired. After getting with Floyd, it looks like the worst case fringe 
field (from ANSYS model) in the PMT area is about 143G (no cladding on 
solenoid). This is good news. It looks like standard 1.5 in. pipe can be 
used. I have asked Amuneal for a new quote for the present mu metal 
dimensions.

Cheers,

       Tim
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