[Lowq] postpone of pass 1 calibration

[fxgirod at jlab.org]

Dear all,

today we had plan to take 1 GeV elastic calibration data, while Hall-A was
supposed to do their transverse measurement followed by a spin dance. As
of this morning, the plan was to go back to 5 pass production around
midnight or 02:00 thursday morning. We unfortunately got delayed and
eventually decided to postpone.

Yesterday was plagued by a vacuum fault in the West arm. MCC was ready to
send us beam around 02:00. At 04:00 this morning, the beam profile was
acceptable (actually quite good). Then we adjusted the beam position by
doing a short X and Y scan. For some reason, around 08:00 when the DAQ was
ready, we lost the beam tune. All our rates became higher, by a factor of
around 10. MCC tried to do some more tune, we never fully recovered the
beam quality that was obtained at 04:00. Discussing at the MCC meeting
today, they had not yet identified what change(s) caused this problem.

At 15:00 we turned into controlled access while MCC was changing the
polarization back to longitudinal, in order to change a HV board for IC.
This was supposed to take 20 minutes, but eventually took 3h. In the
meantime, Hall-A got ahead a little bit of the scheduled plan. It then
seemed more reasonable to re-establish 5-pass production right away.

As of right now (22:30), we have an acceptable beam (admittedly without
optimized BOM rates, around 50 Hz), and have an established production
beam tune. MCC just called to take away the beam for half an hour, after
the spin dance was finished.

The cause of our problems has been attributed by MCC around 16:30 this
afternoon to an injector double beam spot issue. I was then down in the
Hall, have no talked directly to them and should know more tomorrow
morning. We should then decide whether it still appears necessary to do a
machine check up between 08:00 and 09:30, as was suggested by several MCC
experts today.

I hope tonight will be more productive. Hall-A preliminary results confirm
the polarization is back as we had before. We have thus not performed a
Moller.

Best regards,
For the run coordination
Francois