[Cuga] JLab schedule/status - A message from R. Ent and A. Freyberger for the Nuclear Physics Experiment Scheduling Committee

[Lorelei Chopard]

Dear User Community,

On the morning of Thursday July 27th, CHL1 suffered a power event that 
resulted in several (but not all) CHL1 compressors tripping off. The 
tripped compressors resulted in a path to atmosphere to allow for 
gaseous He to escape (which is the nominal situation when *all 
*compressors trip off). Unfortunately several compressors remain active 
and this resulted in a large volume of air being pulled into the CHL1 
Helium space. CHL1 was severely contaminated and inoperable at this point.

At this point in the Summer shutdown, CEBAF was at 4K on CHL1 and CHL2 
was at room temperature for maintenance, but in an operable state 
(maintenance more or less completed). The estimate was that CEBAF could 
last about 48h without 4K CHL operations. CHL2 cooldown started mid-day 
Thursday and CEBAF slowly lost LHe levels (clean gas was captured, dirty 
gas was vented). CHL2 was able to liquefy Helium Saturday afternoon at 
which time several modules had past the no-return point. Cryo cooled and 
maintained modules that had not passed the 50K level and those that had 
were allowed to warm up to room temperature.

By Sunday about half of CEBAF was cold (but not full). By Monday 
Cryogenics had cleaned contaminated purifier and was in the position to 
purify He gas and fill some of the modules that were cold. This effort 
continues to this day. Next week Cryogenics and SRF will start the 
process of cooling down the warm modules. This process will take a bit 
less than one-month.

At the time of the incident,  two months of shutdown work remained to be 
performed, including testing/recommission cold-box SC1 which failed in 
March. We are still evaluating the tasks/sequence to recover CEBAF. The 
estimate is that sometime around mid-November CEBAF will be in a 
position to support beam, with beams for Physics after Thanksgiving. 
This is a very rough estimate. We are working on an experiment schedule 
for the remaining of 2017 and all of 2018 based on this estimate.

This event is what Ops refers to as a "unplanned" warmup, not to be 
confused with an "uncontrolled" warmup (aka hurricane Isabel). As such 
the modules warmed in a slow manner as vacuum was maintained during the 
warmup (although we wish it was slower). Nevertheless there might be 
some impact to SRF performance associated with this event. We are 
working with Cryogenics to develop the quickest route to 2K so that we 
can evaluate the SRF performance. In the meantime, assuming worse case, 
we are readying the two hottest cryomodules in the LERF to be installed 
in CEBAF if it is determined that there is a need for this action. The 
present sketch suggests that we might be in a position to answer these 
questions by Oct.

The Lab Director has formed a Root Cause Investigate team, led by COO 
Mike Maier to look into the root cause of this event and recommend 
corrective actions.


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