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User name D. Parno
Log entry time 01:17:11 on May 16, 2009
Entry number 273767
keyword=Compton Polarization History May 9 - 15Attached are two plots tracing the behavior of the Compton asymmetry over the last week or so. The first run shown is from the evening of May 9 (starting about 6 pm) and the last run shown is from the afternoon of May 15 (ending about 4:30 pm; Compton events present only until about 2:30). We do not have runs later than that afternoon because the Compton laser cavity stopped locking at that time.
The asymmetry is plotted separately for the laser left-circular polarization state (blue) and right-circular polarization state (red). These two asymmetries will have opposite sign due to the way they are defined. Fig. 1 shows positive asymmetries (more positive -> higher polarization) and Fig. 2 shows negative asymmetries (more negative -> higher polarization).
There's a lot of scatter, but you can see that there's no dramatic trend in the polarization over the last week or so. If you focus on the last few runs, you'll see that the colors switch signs at Run 16917 (10:55 a.m.), corresponding to the switch in half-wave plate status at the injector. The next run (16918) is the first one taken after the spot change. That group of runs does display a higher polarization than the previous runs, but it's difficult to say that this is due to the spot change, given that Run 16917 (before the spot change) also displays a high polarization, and given the amount of scatter in previous runs. When the Compton is restored, it will be interesting to see whether that higher polarization has been maintained.
(A note about the plots: where runs are missing, it is generally because
(1) they were too short (a few minutes) to measure an asymmetry, (2) the
beam current was too low or (3) they were run in a mode without photon
data, e.g. for diagnostics.
A copy of this log entry has been emailed to: riordan, doug, camsonne
Figure 1
Figure 2
