During the day shift, beam polarization studies were carried out in
conjunction with the Accelerator Physics Group. The electron beam was
initially displaced by several millimeters horizontally in the Compton
Polarimeter Interaction Region from its pre-Thanksgiving location. Some
time was needed to resteer the electron beam and the laser. Measurements
were then carried out to determine whether we were losing any polarization
for high currents in the Ring. Unfortunately, it proved to be impossible
to store more than 50 mA at any point during the shift. On the bright
side, no change in the polarization as a function of injection current was
observed for the present tune. Several other betatron tunes were also
tried, although our data set was less extensive than we had hoped. There
appeared to be a slight loss of polarization at one point, but we did not
see the type of dramatic polarization losses which had been observed in
some pre-shutdown runs.
Beam polarization measurements are coming out at about 65%. There is a
steady false asymmetry of a few percent and measurements with the
polarized source half-wave plate in are consistently higher than
measurements with the wave-plate out.
The insertion of polarimeter events into the BLAST data stream is not
working right now. The Compton polarimeter DAQ is presently being run in
stand-alone mode and the event streams will have to be combined in replay.
The web documentation on how to do this is not up to date, but Tancredi
wrote notes in the BLAST log book on some basic steps (starting and
stopping runs, etc.). For tonight, at least, this will be good enough.
Bill
-- ********************************************************************** Wilbur A. Franklin * Phone: 617-253-9518 Bates Linear Accelerator Center * FAX: 617-253-9599 P.O. Box 846 * Email: wafrankl@mit.edu Middleton, MA 01949 * **********************************************************************
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