Quick summary: We've been able to get to DRMI_TO_POP and can now engage most of the DRMI ASC loops. Jim and Jeff are currently looking into an issue with the HAM yaw motion that might help explain the optic moves that we've had to make.
- PRMI will lock breifly but then quickly lose lock. This was from the ASC PRC1 gain going from 12 to 5, we bumped this up from 5 to 8 in lscparams for now. Might need to revert later.
- Tried walking PR3 in the direction that it has been moving (in the -yaw) and compensate with PR2, this didn't seem to help. We moved suspensions back to our best buildup position within this movement.
- We managed to lock PRMI and then DRMI with this alignment. We kept DRMI ASC off because the error signals were not well centered, and attempts to center were not sucessful. Most noteably INP1 and PRC2, but others were off as well. We decided to try moving past DRMI with only the MICH ASC loop engaged. We then made it up to DRMI_ON_POP, so past a CARM reduction and technically made it onto POP @1f.
- We've now repeated this a few times with little or no alignment changes, so we will step through the state by hand to find if there is an exact spot that it is failing.
- Jim had a look at the HAM CPS residuals and noticed that they have been exponentially driving away for the last ~45 days (plots attached). This might line up with the adjustments we've had to make in the input arm. Jim and Jeff are currently investigating.
The attached screenshot (taken with the nice flameshot gui which allows easy annotation) shows part of the story of what has been going on.
The top left plots shows the DC power on the LSC pop diode, normalized by input power. This beam is transmitted by PR2 and shares an optical path with the ALS beams as they head to HAM1 and ISCT1. There is one drop in normalized power on this diode about 60days ago, then another drop when the input power was increased. Over the last 2 weeks as the ISI drifts have accelerated, we see the power on the diode dropping further, indicating clipping on this path. You can see in the top right plot the PR3 slider, which has been adjusted over the last 2 weeks to increase the ALS beatnotes, these PR3 steps did partially restore the power on LSC POP, but not compeletely.
This helps to explain why we have re-aligned the ISCT1 table so many times this week.
The problem was that the HAM-ISIs were all drifting off in Yaw (RZ) slowly, but surely, for weeks -- see LHO:69934.