[Prex] run without Compton

[Simona Malace]

Hello All,

I offer *zero guarantees* that the Moller would work (efficiently) as the only source of polarization measurements in Hall A.

The Moller target magnet quenched during the last 2 Moller measurements in March so those measurements were not completed.
>From this narrow perspective, at least, I don't think it's a good idea to rely just on the Moller.

Simona


________________________________
From: Jay Benesch <benesch at jlab.org>
Sent: Saturday, August 29, 2020 8:03 AM
To: prex at jlab.org <prex at jlab.org>
Cc: Camille Ginsburg <ginsburg at jlab.org>; Cynthia (Thia) Keppel <keppel at jlab.org>; bteam at jlab.org <bteam at jlab.org>; Simona Malace <simona at jlab.org>
Subject: run without Compton

Colleagues,

I suggest the beam be steered straight through and the Compton system turned off.  Rely on weekly Moller measurements for the remainder of the run.   The source, injector, beam transport and operations groups have not been able to find a solution which allows low Compton background in A and 30 uA to C without 0R08 BLM trips since the FY20 run began.  We are unlikely to find one in the next three weeks.  The laser swap between B and C helped but was not sufficient.

CREX has received 444 C.  While online cuts classify only two-thirds of this as "good", my observations of all JLab parity experiments suggest that at least 90% will be made usable in final analysis.  In 20 days of running straight through, another 100+ C can be delivered.

Data obtained to date can be examined during the cryo down and possible mitigations proposed.  Given that the source group must buy COTS lasers (commercial off the shelf) and the four lasers now installed provide quite different results, I fear that the only solution will be to buy several more systems and pick the four best for use.

Jay
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