[Sbs] RC update: All shifts canceled until holiday shutdown and RC meeting today

[Andrew Puckett]

Hello all,

I wish I could bring you better news. In light of yesterday’s cell rupture event, it is clear we will not be bringing beam back into Hall A before the holiday shutdown. I am canceling all remaining shifts until the holiday shutdown.

RC update:

At approximately 16:42 during swing shift yesterday (Dec 14), the shift crew noticed a “massive HV trip” of all of the BigBite GEMs and also the GRINCH:

https://logbooks.jlab.org/entry/4101677

At the time, Gordon and Hunter were in the CH. While assessing the situation, Hunter saw a target chamber temperature spike similar to what was seen during the previous cell rupture event in November, correlated in time with the detector HV trips. An NMR was performed on the pumping chamber, and no signal was seen, confirming that target cell Hunter had ruptured. Zooming in on the time of the event, we found that a large (~9 mm!) BPM Y (vertical) position excursion happened without tripping off the beam for nearly 5 seconds:

https://logbooks.jlab.org/entry/4101739

This was also associated with a large spike in radiation in the Hall:

https://logbooks.jlab.org/entry/4102088

Around this time, there were also some vacuum issues developing in the upstream beamline. Failure of the upstream Be window is suspected, but not yet confirmed.

Once the situation was understood, we powered down all detectors and spectrometer magnets, turned off and locked out the target lasers and the target oven, sent the swing shift crew home, and immediately canceled owl and day shifts for 12/15. This morning it is clear that there will be no more beam before the holiday shutdown. Your RC is working to get RadCon support for cleanup of the target enclosure (the tech on call has been notified), and the spokespeople are discussing what work can still be accomplished before the holiday shutdown to keep the existing plans and preparation for Kin. 4 on schedule.

We will hold an RC meeting today at the usual time of 3:30 PM today to continue the discussion:

Location:   Counting house conference room

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Sincerely,
Andrew

Andrew Puckett
Associate Professor, Physics Department
University of Connecticut
196 Auditorium Road, Unit 3046
Storrs, CT 06269-3046
Office phone: (860) 486-7137
https://puckett.physics.uconn.edu<https://puckett.physics.uconn.edu/>
puckett at jlab.org<mailto:puckett at jlab.org>
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