[Xrayops] Emittance fluctuations yesterday

APS Experiment Hall X-ray Operations Problem List xrayops at mailman.aps.anl.gov
Thu Oct 26 12:13:21 CDT 2006

Operations was seeing changes in the horizontal and vertical emittance 
yesterday morning. We now believe the problem with the horizontal 
emittance was due to an instability which occurred when individual bunch 
current was above some threshold. This instability was also reflected in 
vertical emittance changes. Increasing the chromaticity late yesterday 
afternoon appears to have alleviated this instability.

We still are seeing fluctuations in the vertical emittance due to 
incomplete compensation for a Circularly Polarized Undulator. Users have 
not reported any problems when these fluctuations occurred in the past 
and a study will be scheduled to address this issue on 10/31-1/1/06.

I've attached a plot of the emittance from 08:00 on 10/25 through 11:00 
on 10/26 to illustrate the emittance changes described above. Any 
feedback will be appreciated.

Karen Schroeder
SR Chief of Operations
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