[Hallb-engineering] [New Logentry] Follow-up Re: Follow-up Re: Hall B cryo investigation and changes to allow operation of Hall B magnets

[kashy at jlab.org]

Logentry Text:
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After looking last night, I found that it appears that the preliminary conclusion that the low amount of flow through the 500L Dewar and thus its return U-tube was most if not all of the problem. 
While looking I saw a strong correlation between the Dewar valve position (see attached plot for signals EV8210.ORBV ) and the flow to Hall B (CFI6711B) {This shows that flow is a strongly dependent variable and that they are closely coupled in time.)

One can also see that the Dewar return temperature in the DBX T(D8522DR) is oscillating quite a bit. from 8.3K down to 6.3K. this is also correlated but with the Dewar supply valve position but there is a lag and a lot of "overshoot". 2K/8K (25% peak to peak variation)

One can also see that the flow to the Hall is raning from 8.9 to 6.9g/s or varying 22% peak to peak

Finally the Pressure in the Dewar (PI8210) is quite stable (~20mbar/1400)  (1.4% peak to peak variation) (or if one wants 20mbar/400 ignoring the atmospheric pressure 5%).

It might be wise and should be possible to stabilize the Hall B system more by switching the input variables on EV8210 (LL8210) and EV8210A (TD8522DR) such that EV8210 controls on TD8522DR and EV8210A controls on LL8210.

I suggest that we have a meeting with Hall B staff this morning to discuss implementation, with folks that are involved with Hall B operation. If anyone else is interested in joining please e-mail kashy at jlab.org and pasyuk at jlab.org to be invited. Eugene, please set up that meeting for anytime between 09:00 and 12:00 this morning or let me know if needs to be another day. Thanks



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