[Hallb-engineering] [Revised Logentry] Torus Vacuum - Maintenance Requirement

[kashy at jlab.org]

Logentry Text:
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We studied the Torus vacuum rise upon shut off and loss of cryogens.
The big vacuum rise comes betwen 35 and 50K. With two vacuum events, (one planned in February 2017 and one that was opertunistic in September 2017) we have determined that the Torus vacuum should be burped every 6 months at the most. These should be scheduled to occur during Hall B beam off periods. Preferably they should be done with a slow warmup. If they must be done faster then they should be done more often.

We should schedule the first one for either December 2017 or January 2018 to be sure  that the time requirement is appropriate. 

As one can see from the plots the vacuum rises very quickly and if it gets too bad the pumps will trip, and then the vacuum may collaspe so much that the vacuum jacket would start to sweat and this will get water on the Drift chambers. 

Process took 3 days in September 2017. We would have started recooling sooner, but we were doing solenoid testing so cooldown was delayed by a day.
We should schedule 3 days but it should only take two.






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This is a plain text email for clients that cannot display HTML.  The full logentry can be found online at https://logbooks.jlab.org/entry/3484681
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