Revision as of 09:22, 22 December 2021

RC summary, December 15-21 2021

This RC tenure is the last of the SRC-CT (E12-19-003) run period. It started with the target filled with LD₂. Wednesday 12/15/2021 saw smooth production on LD₂ at 140 nA, 0/90 para and perp. It was interrupted only by ~1h of RF-related beam down time and a search for better spot on diamond JD70-105 since it had degraded due to beam damage. H. Egiyan tried to find a new location that improved the 0/90 para and 45/135 para/perp coherent peaks, but to no avail. Good data taking continued on Thursday, 12/16/2021, with about 6h of beam-related interruption. The only (small) trouble was that the target control computer needed to be rebooted. This did not caused time loss, but the target LD2 nominal temperature after reboot was 1.3K lowerer than before the reboot. After the Thursday morning run meeting, SRC-CT leadership decided that the experiment would benefit from changing the target from LD₂ to ⁴He the next day (Friday, 12/17/2021. This was a long discussion because none of the Target Group persons who knew how to do the change (C. Keith, J. Maxwell) were available. Eventually, C. Carlin agreed to do it with C. Keith, who was out of town, writing a detailed procedure and supporting by phone. On Friday, 12/17/2021, LD₂ (140 nA, 0/90 para and perp) data taking continued until 14:10, followed by a 1h empty target run since such data were needed and the target had to be first emptied. (This failed at first because the target cell boiler used to evacuate the cell would not respond. C. Carlin asked for Rapid Access and fixed the issue. This problem reduced the empty target run from the planned 2h to 1h). The target gas change went relatively smoothly and was done within the expected time. A planned Rapid Access was done for switching gas. A. Somov, L. Penchev, S. Botarinov and V. Berdnikov took advantage of that access to re-position the calorimeter prototype in the Pair Spectrometer test area. while the target ⁴He gas cooled down (a process taking about 3h), the Hall was closes and A. Somov requested the beam for opportunistic Pair Spectrometer background data taking. Around 23:00 (12/17/2021) the ⁴He reached its nominal temperature and SRC-CT was ready for production but the beam was unavailable. the beam was unavailable. It came back at about 1:50am (Saturday 12/18/2021) and we started production on ⁴He (150 nA, 0/90 para and perp). The rest of Saturday went very smoothly, with data collection on ⁴He (150 nA, 0/90 para and perp). However, Sunday and Monday were less efficient. We got, out of 48h, only about 15h of production on ⁴He (150 nA, 0/90 para, perp, and amorphous). There were 2 long down times: ~5h between Sunday 9am-13:45 (multiple causes. Mains ones: Bulk power supply and 1L04 zone RF issue) and Monday (1am-10:30am due to IL05 zone RF issue). In addition, to ⁴He production data, about 6h was used for CPP trigger tests and 3h trigger tests in raw data mode. (Both tests were conducted by A. Somov). On Monday (12/20/2021) a target pressure event occured due to large vacuum spike in the Outer Vacuum Can (OVC) of the target. This had no incidence on data taking. (Most of the event unfolded during beam down time in any case.) Eventually, the cause of the events was trace back to a faulty turbo pump. The vacuum degradation caused the target temperature to slightly increase. We continued production on ⁴He (150 nA, 0/90 perp only because para was too degraded) until Tuesday (12/21/2021) ~3:30am, gathering a final ~6h of data on ⁴He. Then we finished the SRC-CT run period with ~3h Empty target run. This was done because more empty target data were needed but also to check if the target vacuum degradation had caused ice to accumulate on the target cell. (This would have happened if the OVC vacuum degradation were caused by a leak. It is only later that the faulty turbo pump was identified as the cause.). On Tuesday, 12/21/2021, at 7:15am, the beam was terminated and the Hall put in restricted access. We started the hall shut down procedure: The beam line was secured by retracting all radiators, putting the collimator in blocking position and turning off the pair spectrometer and sweeping magnets. M. Stevens ramped down the Solenoid, put on the beamline windows and completed the rest of the technical shut-down checklist. C. Keith secured the target will already be empty. L. Penchev and A. Somov turned High and low Voltages off as well as the wire chamber gas and chiller. Crates were be kept on.

For this week of RC tenure, we got 84h of Accceptable Beam in Use (ABU) out of the scheduled 136h, therefore a 62% overall efficiency.

For the whole SCR-CT run, there were 41.3 days scheduled (43.3 days total, but 48h were spent in beam studies). Therefore, the overall ABU was 60.7% (601h), or 60.1% (595h) if we account for the 6h of CPP trigger test (not part of the SRC-CT run). Assuming the usual 50% run efficiency and using the 21 pac days allocated to the experiment, SRC-CT gathered 118% of the expected data. As usual, this number is for accounting only and does not account for details, like data taking overhead higher than expected (e.g. due to radiator swaps, reducing the data taking efficiency), or the fact the SRC-CT run used a coherent enhancement that effectively favored better kinematics (increasing the data taking efficiency).