Run Coordinator report: Fall 2018 w13

Run coordinator report for the week of Nov. 14-21 2018. A. Deur

The week was shared between systematic studies and production on the 47 um diamond/5mm collimator.

Beam delivery was in general excellent but its optics quality did not meet the specifications: the size of beam was generally too large. In particular, its size at the collimator was typically more than twice wider than the GlueX specs. Two attempts were made by Todd Satogata and Jay Benesch to correct the problem but they were unsuccessful. The first attempt took place on Wednesday 14th and a good beam profile seemed to have been obtained. This was followed by a 8h TAC run during which the optic seriously degraded for reasons not understood yet. The second attempt was made Monday 19th. Todd saw that the beam size was too big at the recombiner and made it smaller. However, it resulted in an increase its size at the radiator. This produced a lot of background, presumably due to beam scrapping. It was assessed that the beam was not usable for production and accelerator backed out of the new optic. In the 2nd tuning process process, it was found that one of the beamline BPM information was wrongly interpreted due to a bug introduced sometime within last month. This partly explained why the tuning of the beam was so difficult for Todd and Jay. In all, 8h were invested in the optic with no gain. It was this decided to stay with the current optics, at least for the upcoming luminosity study (see below).

The consequence of the large beam size is that the beam transmission is significantly lower than two weeks ago. We are currently running at rates 18% lower than the optimal ones. This is the lowest transmission for the Fall 2018 run.

Beside production on the 47 um diamond/4.5E-4 Al. radiators with 5mm collimator hole, we did a few special tasks:

1) A TAC run on Monday with 30 nA beam current and the V-wire. It was successful and is similar to the previous runs, demonstrating the stability of the TAC and calibration; 2) An empty target run and a raw mode run while the target refilled, both done following the Monday TAC run; 3) A short FCal high voltage scan on Tuesday; 4) On Wednesday, we started the program of systematic studies of the equipment performance at different luminosities. This was preceded by a pedestal calibration for several of the detectors.

By the end of my RC tenure, we were about half-done with the data taking on diamond for the luminosity systematic study.