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20170110 ┬╗ Diffuser_field_test.txt

Diffuser field test? - Cobb, John, 10 January 2017 11:49

 
1
´╗┐Iris 4 of the diffuser (the thickest one) stuck in the closed position towards the end of the last run.
2
The magnets tripped and when Joe T from Oxford came to examine the diffuser a few days later, that iris was found to operate normally. The diffuser was not, therefore removed (which is non-trivial).
3
It is possible, therefore, that the sticking was caused by the magnetic field in SSU. All the irises, including iris 4, had, however, been operated previously with the field on.
4
All the components are nominally non-magnetic although there are some stainless steel components that have a small permeability and will feel a small magnetic force.
5
The sticking of Iris 4 is therefore mysterious but may have been associated with the magnetic field plus time plus some mechanical wear.
6
Is it desirable, therefore, to run up SSU before the next run and test the diffuser?
7
I doubt that a fix could be effected in time if iris 4 is found to stick with the field on, but it could be left open / disabled for the next run.
8
Alternatively it should be tested at the very start of the next run with the overhead of having to run down / up the magnets if it is found to stick.
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