Doug and Wang on shift.
Previous shift had problems with signal to background for wire chambers.
Dumped the beam, turned off the WC HV, and waited 1 hour. Solved the
problem. Suspect when previous shift thought the HV was off that it was
only in STBy which isn't sufficient. How the WC's became noisy is not
clear but suspect they were on while CCR tuned the beam yesterday evening
after we were open to fill the snakes, etc.
Took five runs with 200 k events each:
563 - empty target, 1/2 wave out
564 - 1/2 wave out, ABS spin 1
565 - 1/2 wave out, ABS spin 3
566 - 1/2 wave in, ABS spin 3
567 - 1/2 wave in, ABS spin 1
Auto-fill software and HV GUI worked very well in general. Twice the WC HV
crate switched itself off and it was necessary to reboot the VME to get
things back. Not sure if this was the best way but it worked.
WC occasionally tripped. Pressing OPER resets the HV fine but it is
necessary to watch the screen as the DAQ is not inhibited for a trip yet.
Remainder of shift was the normal running: ABS flipping 2 state, 1/2 wave
plate changed for each fill.
Changed CCR current set point for new fill to 60 mA to maximize luminosity
assuming 2.5 minute dead time and 25 minute lifetime.
At end of shift chose to switch to unpolarised gas system and do background
studies. Closed V11 and V14 of ABS but otherwise left it on. Turned on
unpolarised system but had a lot of problem getting it to work. Eventually
determined the three manual valves on the target chamber were closed. With
Chris Vidal directing via phone opened these valves. MFC on unpolarised
system seems to be unable to regulate at flows equivalent to ABS. In the
end set it to 0.08 and the read back was 0.05 which seemed to be the
minimum value. Ligit pressure with ABS was 1.8*10**-7. Unpolarised at
0.08 sccm corresponded to 3.5*10**-7.
Plan for tonight should be to run unpolarised for one shift
flipping beam helicity for each fill. Then close all gas to the target
cell and run with an empty target for one shift. Remember to watch the WC
for trips and start the Compton Polarimeter runs.
Cheers,
Douglas
26-415 M.I.T. Tel: +1 617 258 7199
77 Massachusetts Avenue Fax: +1 617 258 5440
Cambridge, MA 02139, USA E-mail: hasell@mit.edu
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