[Hallc_running] Reminder of Beam Recovery Procedure and Operation Restrictions

Xiaochao Zheng xiaochao at jlab.org
Mon Feb 10 14:08:24 EST 2020

Dear All:

I'd like to point out that the polarized 3He target cell used by the A1n/d2n experiment is a fragile, high-pressure gas cell. You do not see it when taking shifts, but they are pressurized to 10-12atm, with glass walls 1mm thick and glass windows (where the beam comes through) 150um thick. It is for this reason we must raster the beam to a specific size, and any movement in the beam position will have a chance of damaging the cell.

Please follow beam recovery procedure closely:


A printed copy is usually available at the Shift Leader console in the counting house. Please read and follow.

--Do not ever skip the beam recovery procedure for the sake of "taking more production data".
--Do not ever allow MCC to send CW beam on polarized 3He cell without first completing the procedure. (And project/calculate the beam size at the target, the harp scan values are not enough. The sigmas at the target cannot be larger than 500 micrometers).
--Do not ever ask for or suggest raster size smaller than 4.0mm diameter on the polarized 3He or the reference cell positions.
--Most importantly, if in doubt (on anything), contact the RC for confirmation.

Also, a screenshot of the Operation Restrictions is posted on the experimental wiki page:
All shift crews (RCs, SLs and TOs) please become familiar with these restrictions. Whatever beam you ask from the MCC should conform to these restrictions.

Thanks for listening.

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