There is an automatic tune sweeper that runs at the beginning and end of
each fill (since last night). This "wiggles" the stored beam a bit to
measure the betatron tunes. The polarization of the stored beam can be
killed by running at certain tune values, so this is one way to be sure
we're not running in a bad place in tune space. The Compton, of course,
provides a measure of the actual polarization.
The tune sweeper runs after the fill has finished, while our high voltages
are ramping up. It also runs at the end of the fill, before the beam is
dumped, while our HV is ramping down. It does NOT run while we are taking
data, in case the small "wiggles" disturb the experiment. They're really
not visible on the BQMs.
Dan Cheever showed me a strip chart which has the tune sweeper still
running for a few seconds when the wire chamber scalers are counting, so
the WC voltages have obviously come up. We don't see any trips correlated
with the beginning of the fill, so I think this is ok. Dan's trying to
make the tune sweeper take less time, but he's not sure he can. If we
decide this is bad for the chambers, we'll have to insert a wait in the HV
control program so the tune sweep finishes before the voltages ramp up.
Karen
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