[Hallb-engineering] [Revised Logentry] Cryogenic Issues in or affecting Hall B

[kashy at jlab.org]

Logentry Text:
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The pressure on the 4K return spiked at ~18:51 and I got a call from Denny a bit later. I was in between home and JLab so I figured the best thing was to come here rather than trying to solve things remotely.

I called Chris Perry of cryo after I saw that things were partially recovering and we discussed possible causes. One concern I had was that the 4K return line could be plugged or plugging with comtamination. This did happen ~25-30 years ago.  We had decided that this was the most likely cause and figured that to be safe we might want to take Hall B magnets to warm return and try to operate them in a "liquefaction" mode. WE discussed this plan with Johnathan Creel and he agreeded that plant protection is the primary thing and if contamination were to enter the cold box it would like shut it down with a long recovery time.

As we were preparing I started plotting the cold return valve position EV6721B.ORBV I notice taht the valve was showing an instantaneous change of postion from 106% to -6.41% and Chris said that this is an EV so that tupe of change is not possible and he is correct. We decided it is likely a read back issue and should investigate the LVDT... Chris said he would be calling in Tech support. 

Upon further review I noticed that the same valve indicated 99.8 % 4 minutes before the Hall B presssure spike started and at that time it jumped to 106% which if it closed significantly it would cause the pressure to rise (the same effect as contamination would have but easier to resolve. Further review shows that the same valve showed motion (real or not correct or not) last week when we had issues with the dewar and Hall B Torus ramping down. 

21:05 Jonathan and Chris came into the Hall B counting House and said they manually opened the valve and removed the control cables.
When the cryo system in Hall B stabilizes back at normal conditions I will ask to ramp up the magnets and get Hall B back in Beam Permit.

21:30 Called Eugene and said while we are not fully back to the conditions prior to this event the system looks good to ramp the magnets and to go into beam permit.

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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/4278263
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