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DSreversal.txt

Comments on reversing DS current - Nebrensky, Henry, 10 November 2011 17:15

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Reversal of MICE Decay Solenoid Polarity 
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Henry Nebrensky
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v1.2
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We would like to reverse the polarity of the Decay Solenoid, as we would like to know two things:
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- is keeping the current in the same direction behind the different speeds we see for electrons and positrons?
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- (if so) does it affect the number of good muons we get?
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There are two steps to this:
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1) we need to confirm the DS can be run at all with reversed polarity, which really means doing it
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2) a series of data runs with the different polarities; at least one e/pi/mu setting  and one mu setting
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For 1): although we do not anticipate any difficulties, the first time we do this we also have to label up all the cables and similar tasks, so it will take much longer than normal to make the change 
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For 2): we need to look at two DS polarities relative to two beamline polarities, implying 5 sets of runs separated by 4 electrical interventions (30-60 mins each) (for which we need an authorised person). Changing DS polarity means stopping and starting the current - i.e. significant quench risk.
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Thus we would need at least a day and a half at the end of the December run - 15/16th Dec.
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Comments/options: 
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a) 1) really needs to be done soon and any issues found and addressed, else we waste a lot of time on false plans
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   I've checked Martin Hughes is available (*at present* only authorised person): _morning only_ Fri 16th, and Mon. 19th.
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b) we could leave 2) until February - indeed probably should leave it until new quench detector available for ramping the DS
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c) Week after Dec. run has been reserved in bulk for ISIS access to substation. *might* be able to run 2) on one day, but unlikely. 
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   1) is more likely - but when must the DS warm-up start?
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Questions:
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 - any other effects we are testing for?