[Primexd] RC week summary, March 6-13

[Alexander Austregesilo]

Dear Collaborators,

I started my duty as run coordinator when the energy of the accelerator 
was reduced from 11.6 to 11.2 GeV for stability reasons. During this 
down time, Chris Keith and Chris Carlin finalized the settings for the 
liquid He target operation and left the operation to the shift crew. 
Beam restoration was expected during owl shift on Friday, we therefore 
staffed the counting house from midnight on and started filling the lHe 
target. The entire day was dedicated to beam restoration, including ion 
chamber calibration, radiation level checks and several iterations of 
harp scans. We had to abandon the plans to perform an active collimator 
scan on Friday evening after the beam position was very unstable and the 
beam was finally taken away to perform a spin dance. In parallel, the 
CDC HV was ramped to nominal values. It was confirmed that the currents 
in the inner rings of the CDC did not reach critical values for nominal 
beam conditions. Around 8pm, we started to take production data on the 
lHe target, 200 nA beam current, 5 mm collimator and a 10^-4 Al 
radiator. During the whole weekend, we saw the y position of the beam on 
both 5C11B and the active collimator drift by several hundred mum, even 
though it was locked on the AC. During the swing shift on Saturday, 
Sasha performed trigger studies and included the CDC into the read-out. 
Unfortunately, a bug in the reconstruction algorithm for straight tracks 
stopped the monitoring system, so the group decided to exclude the CDC 
for the rest of the weekend. On Monday morning, this problem was fixed 
and the CDC could be included into the data stream. After a rapid access 
to reset the communication to the ComCal HV main frame, the beam 
position was stable enough to perform a scan of the active collimator, 
which resulted in a about 10% higher transmission at the new nominal 
position (-0.1, 0.0). For the rest of my tenure, the conditions for 
production data taking were extremely stable. Out of the 91.5h of CW 
beam on target, we could use 87.2h (95%) and recorded almost 8 billion 
triggers.

(from 
https://halldweb.jlab.org/wiki/index.php/Run_Coordinator_report:_spring_2019_w7)

My sincere thanks go out to all shift crews and experts on-call during 
this week.

Alex