Run Coordinator report: spring 2019 w9
This week of PrimeX running was quite smooth. We took production data from Wednesday until Sunday afternoon. At 5:30pm on Sunday, we emptied the liquid helium target to take some empty-target data. This continued until late on Tuesday morning after RF recovery began, when we refilled the helium target and continued with helium target production.
Besides mandatory breaks in production during day shifts on Monday and Tuesday for machine development and RF recovery, respectively, data taking mostly continued uninterrupted. Out of 144 hours scheduled for this week, we had 96 hours of acceptable beam, of which 91 hours were used for physics. The 4 lost hours were due to the failure of a HV crate that powers the CompCal (90 minutes), various DAQ problems (90 minutes total), failure to turn on the TOF HV before starting the run (30 minutes), and time required to reset the voltage on tripped channels in the FCAL (30 minutes). Problems with the beam position wandering off from the nominal values at the active collimator was greatly reduced by the accelerator increasing the sensitivity in the slow controls loop for that circuit. The beam energy was drifting around over the course of the week by roughly 8 MeV, which prompted the MCC operator to make an adjustment to the tagger dipole magnetic field at one point. We asked the operators to please inform us whenever they need to make such an adjustment in the future.
Variation in the transmitted photon rate through the collimator per nA of electron beam current, as measured by the coincidence rates in the PS, have been varying by 5% since the start of the Primex run period. It was suggested that these variations might be tied to times when Hall C beam was not present, but this correlation was not observed during this week's running. We also continued to see a drop in the Primex physics trigger rate relative to the PS coincidence rate over the course of the week. The cause of these variations is not understood at present.
At the end of this week, the integrated ABU for the Primex helium measurement has now reached 91% of the total approved time for this experiment in spring 2019, while only 72% of the calendar days for this run have passed. The figure below shows the 2-gamma spectrum derived from Primex events with two clusters in the FCAL, showing a clear peaks for the eta(550) and also for the omega(780) where one of the gammas from the pi0,gamma decay was not detected.
