[Rgc] RC daily update - July 27 - RC meeting today at 2:15PM

[silvia at jlab.org]

Hello all,
Yesterday's day shift started with problems with a DC crate, that required
an access. Beam was quite unstable, but we managed to take some runs on
negative ND3 (NMR polarization ~24%). At the beginning of swing shift we
asked to flip the HWP to OUT and tried the procedure that Stepan had
suggested to reduce the beam-charge asymmetry playing with the attenuators
in the Moeller GUI. This however seemed to yield no effect (and today we
learned that the values we thought we were changing were not being
transmitted correctly https://logbooks.jlab.org/entry/4020514). Then we
decided to resume data taking. Chris Keith was having some success in
finding a good MW frequency to improve the slope of the negative
polarization. Then a storm came and, suddenly, everything died: CEBAF, the
ESR, our magnets ramped down (the solenoid may even have quenched).
Luckily Chris and James Brock were in the CR, they took measures to save
the target from warming up, as the ESR was dead. One ECAL sector went off,
we went to controlled access to reset a CAEN HV module. The ESR came back
to life at around 7PM, and CEBAF seemed to be recovering fast. The target
guys restored its normal cooling modes, and Denny started the cooling down
of the magnets. The cooldown of the torus was quite fast. The solenoid
took a very long time. We got the OK from Denny to start ramping up the
magnets at 1AM. Once the solenoid ramp was almost at the level for the
baseline NMR measurement, I went to the Hall with Richard to reset the MW
power. Then James Maxwell took a baseline, we ramped up the solenoid to
full field, and James started repolarizing. The polarization seemed to be
increasing at a very fast rate, much better than last Sunday. We went back
to beam permit and gave MCC the OK to take beam, but unfortunately it has
not come back yet, as they're still fighting with various problems. The
plan is to start taking data as soon as beam comes back. The NMR right now
reads 28.4% and it has a very nice descending slope. I am no longer sure
we should flip the solenoid already tomorrow, if the target behaves so
well maybe we could just anneal it and postpone the solenoid flip to the
next downtime next week? TBD in our meeting today. In any case, Bob and
Denny are both looking into the procedures to flip the solenoid field.
Link for our RC meeting of today (the usual one):
https://jlab-org.zoomgov.com/j/1608674253?pwd=SFZyYmZLWXJieGtpV2dEdVRiUEJnUT09
Passcode: 786506

Best regards,
Silvia, RC - just for a few more hours, thankfully! :-)