[Hallb-engineering] [New Logentry] Hall B dewar disconnect and 4K circuit purification check and cleanup

[kashy at jlab.org]

Logentry Text:
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The Hall B dewar was disconnected from the DBX per ePAS 5741 rev1

The next step in getting ready for cooldown is to check to see if any significant contamination exists in the 4K supply circuit.

Flow to check contamination per phase 1 sketch was established at 13:50, 13minutes later the contamination level at the purifiers (CCT10N21R) peaked at 2.9ppm and recovered back to baseline of 1.3pppm approximately 30minutes later.

We will proceed to go to phase 2 which will allow flowing thru the rest of the circuit overnight by 
1) lower the amount of flow through the Dewar supply bayonet (a manual valve in Hall B)
2) Closing 4K supply valves in the magnets
3) Adding flow through both 4K supply valves backward toward ESR by flowing 300K 4atm gas  from the CD circuit PV8563W in the DBX through the PV8566T to PV8512T and through PV8566S to PV8512S 

By morning we should have a fully warmed and clean 4K supply circuit.

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