Sheila, Jim, TJ, Jenne

TLDR: PR3 optical lever calibration seems wrong by a factor of 4, for some reason it didn't witness the ISI problem of last week. 

Last week we had difficulty with alignment, (69924, 69907 and others), before realizing that there was an accelerating drift of HAM ISIs (which Jim has now installed a fix for 70006).  One thing that has been bothering me is why we didn't catch this faster, especially because we looked at PR3 optical lever trends many times and didn't see a drift. 

The first attached screenshot shows the time when the ISI was reset, resulting in a 8urad shift of the ISI shown as about a 2 urad shift in the optical lever.  (ISI channels are in nrad, sus channels in urad) When the suspension slider was moved by 2 urad after that, the optical lever sees a shift of 0.5 urad, so this seems to indicate that the optical lever is seeing both of these types of shifts, just with a factor of 4 calibration error.  

The second attachment shows the longer term trend over 1 month, where the ISI is drfiting by 8 urad.  We should expect to see a 2 urad drift in the optical lever corresponding to this, but the optical lever doesn't show this trend and has less than 1 urad long term drift. I don't undertstand this.  

The third attachment shows the weekend incident where Tony had to ajust PR3 alignment again, 69980 .  The ISI, HEPI and the top mass yaw don't show a shift, but the optical lever does show that when Tony set PR3 to restore the ALS COMM beatnote, he brought PR3 back closer to the alingment it had been at Friday when we aligned that table.  Betsy points out that the PR3 top mass osems are moving by 20um with changes in the LVEA temperature, which might have contributed to this.

See also TJ's check of LVEA temperature and suspension drifts: 70000