Corey, TJ, Sheila

Sumary: We've had some clipping in the PRC, which has been getting worse over the last couple of weeks.  This could easily be the cause of our bad noise, and locking difficulties.  We had some sucsess unclipping it by moving yaw, but we aren't yet back to the POP18 build ups we had in mid November. Sensors for looking at PR3 drifts are confusing.

Corey was struggling with PRMI locking this evening.  When I logged in he and others had been working through initial alignment steps, and Corey was able to lock PRMI but with low buildups.  Corey and I spent some time looking at some history of POP18 build ups when PRMI is locked over the last several weeks:

• 11/10 22:29utc 98cnts
• 11/17 10:57utc 91cnts
• 11/25 19:04 UTC 80 cnts (DMRI 96)
• 11/28 1:41 UTC 87 cnts (DRMI 100)
• 11/28 7:32 UTC 85 cnts (DRMI 96)
• 11/28 22:24 UTC 80 cnts
• 11/29 2:18 UTC (a bunch of PRMI locks) 73 counts (DRMI 82)
• 11/29 5:22 UTC 70 cnts (DRMI 80 cnts)
• 11/29 21:16 UTC 62 cnts
• 11/30 1:56 UTC 58 cnts (DRMI 82 cnts)
• 11/30 14:39 UTC PRMI 56 cnts
• 12/2 4:37 UTC PRMI 52 counts

As you can see, the POP 18 build up has been slowly decreasing, even in times when we were locking. We then ran PRMI ASC (REFL 9 to PRM, AS 45 to BS) while we moved PR2, and saw that this did have an impact on the build ups, which it shouldn't if we aren't clipping. (see first attachment for pitch move of PR2).  This pitch move made the build ups more stable, but we couldn't improve the build up with PR2 pitch alone.  We saw similar behavoir with yaw, and moved PR2 yaw in the negative direction.  The second attached screenshot shows a walk of moving both PR3 and PR2 in the negative yaw direction, which did increase the POP 18 build up to about 80 counts.  This was done with ASC off. 

At this time we had trouble keeping PRMI locked for a little bit, it looked like the "mitosis" glitches that Ibrahim saw Wed which we believe were caused by the BS oplev (BS optical lever damping runs while PRMI ASC runs, we tried to turn it off but that was unstable).  We tried a few more rounds of yaw walking with the ASC off, but we saw POP18 drift up to 86.  I think the next step would be to try to walk PR3 and PR2 in pitch to get back to the POP18 build ups close to 100 that we had a few weeks ago, Corey is trying that now.  We probably would be able to lock the IFO with the current value of 86, if all else fails (but if we are still clipping in the PRC that could be causing bad noise).

What's the drift?

The third attachment here is a trend of several sensors of PR3 alignment over the last few weeks, they do not agree with each other.  The optical lever would indicate that the drift of PR3 has drifted in the positive yaw direction, while the top mass osems would indicate that it has drifted in the negative direction.  When I moved PR3, both sensors agree that the sign of the move was negative yaw, so there is not a sign error in one of them.  This reminds me a lot of 70008, and the incident that inspired that alog where the ISI was drifting so the suspension osems didn't show the drift.  TJ points out this alog about the PR3 sensor calibrations: 70197