The results of the recent A2L measurements for PR2 and PR3 are analyzed. Here is a summary.
| (coarsely) averaged Y2L or P2L gain [cnts] | alpha at UL osem | spot position from the center of optic | |
| PR3 PIT | + 0.85 | + 0.088 | 4.61 mm too low |
| PR3 YAW | + 1.8 | -0.19 | 18 mm toward West |
| PR2 PIT | 0 | 0 | 0 |
| PR2 YAW | -9.5 | 0.45 | 19 mm toward West |
Synopsys
The horizontal spot position on PR2 may sound too large, but I don't think this is bad.
Back in 2014 we adjusted the PR2 spot to be at 14 mm toward the West (14788) in order to improve the clipping situation on PR2 based on the study that Keita did (14640). Since the beam radius on PR2 is about 6 mm (see for example 30130), the spot position seems to have shifted by roughly the radius of the beam size further to the West comparing to the 2014 measurement. Note that the size of the PR2 optic is 150 mm in diameter (D1101377). According to these numbers, I don't think the measured spot position is too crazy.
Some details
Over the past week or so, the operators ran the a2l scripts for PR2 and PR3 (for example 31239). The scripts were the ones Jenne newly wrote specifically for checking the beam spot on these mirrors (31157). The attached shows trend of the a2l gains for the past two weeks. The values are then roughly averaged and used to estimate the typical spot positions as listed above. For the definition of alpha, see Koji's log entry in the 40m elog. For the conversion from alpha to the spot positions, see 14788.
