Update:
Arne, Reza, Riad, Jay and Todd have been working very hard this afternoon on the new injector tune and trying to get us our long awaited "stable high intensity beam". Now that the injector optics tune is in better shape than previously, and they are still having trips in the injector, they suspect a problem farther upstream. No clear signal of what it is yet. The symptom is that the optimum relative phases of the acclerating cryomodules, as I understand it, are not stable in time. This leads to increasing halo rates and beam trips. This is persistent for many days now.
They are now focussed on temperature changes in the injector. Avid followers of the beam saga may recall that they were suspicious of these earlier in the week. A heater was installed. Then it seemed to get too hot. They turned off the heater and plugged up an outside air vent yesterday morning. Had no great improvement in beam stability. Then found a better injector tune and tried it today. Just as they were getting beam back from that, some mysterious process turned the heater on again. They found a significant temperature excursion correlated with phase drift and deteriorating beam conditions. This occurred early this afternoon, but became the focus of attention closer to 6 pm. The heater was turned off around that time and they are waiting till 7:30 (ie about now) for the temperature to stabilize, then Reza will once more try to tune up the injector and various RF phases for us. My guess is that this is likely to take until 8:30 pm or a bit later.
MCC Elog entries of interest:
Injector Heater / temperature: https://cebaf.jlab.org/elog/entry/1566472
Matt Poelker's comment on it: https://cebaf.jlab.org/elog/entry/1566475
Mike Tiefenbach's explanation of the double peaking in BPM3C12X: https://cebaf.jlab.org/elog/entry/1566487
Plan:
Let's run on LH2 overnight with whatever they can deliver us. I'll need diagnostic plots, strip charts, the works, for the 7:45 meeting tomorrow morning. Take extra care to make sure the charge feedback loop is working ok. Watch the Compton scintillator rate and alert MCC if it goes above 5kHz / uA at 100 uA or above. Reduce the beam current a little is necessary, but hopefully some phase adjustments would bring it back to a reasonable level.
Don't let them do significant beam tuning on ANY target under these conditions!
Shift crews please make nice plots:
Also, please investigate BCM 5 - 6 performance with the new electronics as per Trent Allison log entry: https://hallcweb.jlab.org/hclog/1102_archive/110203171522.html
Thank you and good luck!