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User name johna
Log entry time 04:44:57 on May23,2002
Entry number 4046
keyword=harp scan problems: Expert please check!
While the recent harp scans were giving odd values (sigma from harp scan = 440 x 3 um for scanner #6), the BPMs (at 70 microA) give sigma= 45 x 30 um. Since the 3 um does not seem realistic, we are ignoring the harp scan analysis results for the moment. We have done the following checks to verify that the BPM resolution allows us to measure the beam spot size:
Run 1570: Harp scan said it was 60x75 (see halog 3479). Bob's BPM analysis (from spot program) gives 27x30.
Run 1761: Pointing run from previous kinematics (presumably around 200x100, but we have to reanalyze the harp scan) gave 45x31 from spot. So the X width is bigger than it was for run 1570, which is what we expect.
Run 1806: Just completed pointing run: Spot gives 63x31. So it looks as though the spot size is too big. We consider this OK for now and will start running.
We would like someone to look at the harp analysis code to find out why it gives the unusual spot sizes for recent runs (e.g. 1732), and figure out how big the beam is relative to previous runs.
Finally, looking at harp runs 1673 (normal spot size), 1674 (small spot size), and 1732 (current run), it appears that the top three peaks are the last harp, and that the current run has a spot size that is ~2x larger than normal. Since the spot BPM analysis also shows it as larger than normal, and since we are running without fast feedback while they try to diagnose it, we will ask for a smaller beam spot.