[Hallb-engineering] [New Logentry] Hall B recovery from ESR down

kashy at jlab.org kashy at jlab.org
Wed Dec 20 16:25:02 EST 2023

Logentry Text:
Hall B was not recovering as quickly as we had in the past from magnet trips.
This was not a magnet trip but an ESR planned shutdown due to breaker maintenance!
The main reason was most likely that Hall C was recovering at the same time.
CFI60DLP showed a very high mass flow rate (35g/s) as Hall C was recovering with priority and this raised the pressure on the return line and thus backed up our flow. Also since the ESR cold box was running and our cooldown return valves were not opening enough, a significant amount of warm flow was going back the 4K return line and thus warming the supply flow to Hall B.  
This was a situation that the PID's for recovery had not been tuned for. So today, we did some manual operation and some automatic tuning and create a new PID parameters and entered the new values in the PID spread sheet and filed it with todays date in the Hall B/CLAS12/Magnets/Cryogenic Ops folder. (The new PID's still might not be perfectly setup so some further work may need to be done). This could involve more similar changes to what we did, (higher Max values, and valve opening rates)  and adding an additional min cascaded PID to EV8522SCD_min and doing more with the buffer dewar. Programing/tuning for non-normal events these types is challenging because improvements only get to be made during off normal events, and luckily for operations and taking beam these events are rare...

The basic change was to force the minimum position of the cooldown valve PV8522TCD higher (was 10% now 20% and could go higher...)
PV8522TCD is a cascaded PID loop. It has two nested sub loops that control the minimum position of the main loop.
One controls on the Torus return temperature TD8522TR and the second controls on the helium level in the lead reservoir LL8120SC. 
The max changes for _min and _min_min loops were also changed a bit to increase the rate of valve motion. 

This should improve future automatic recoveries.

NOTE: ESR operators probably should have and can always close the 4K return valves on Hall B when the magnets are not ramped up, the systems are designed to be fail safe. (They are safe in all modes, but that type of thing will certainly cause the magnets to discharge and should not be done without consulting Hall operations and the Physics Division Cryogenic coordinator (D. Kashy))

I was consulted about what should be done for the Halls and did not think to ask ESR to close the 4K return valve to Hall B or other Halls after the ESR was shut off. This would have somewhat reduced the recovery time.
As it is Hall B is now fully recoverd and back to normal 4K operation, approximately 8 hrs after the ESR was shut down.

Happy Holidays to ALL!

I increased the maximum output of both sub loops from 10% to 20% and this forced PV8522TCD further open this in turned require the cold return valve 


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/4236023
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