We had another lock of about 40 seconds, durring which all the signals seemed more stable than last night. It was knocked out by an oscillation that showed up in boh the MICH WFS and MICH length loops. We added an extra boost (2 poles at 0.1 and 2 zeros at 2Hz) to the CARM path, which seems to have made things more stable. The lockloss time was 11:56:32 UTC Feb 5th.
Today we saw that our alingment was drifting much more quickly than we had seen in the last few weeks. Without ASC we could only lock DRMI for a few minutes before MICH would get misaligned. The attached screenshot shows the slow drift of ITMX pitch, the red trace, which is about 1.5urad over the last 3 hours. We are not sure if this is real or just OpLev drift. Wspent some time on the MICH ASC loops. We phased ASB 36 so that the BS shows up in Q, and saw that this is a better signal for the WFS throughout the CARM offset reduction, which is what Ryan says they saw at LLO as well. They come on with a bandwidth of about 1 Hz, and hold the DRMI buildup is stable.
We also ran into difficulty tonight with the PSL rotation stage, it stopped responding to the command button for several hours. We need some code that checks if the input power is really the requested power, or we could try running through the whole sequence at the same power.
Here is a StripTool of the lock acquiistion. My DTT trend is taking too long to run, and I am tired...
I have attached the temperature plot during the lock time (time at lock loss - 2 hrs). To see if the ITMX pitch drift was real I attached the vertical dof of the top stage as well...
The LVEA average temperature is taken from many sensors. Here is a map of the individual temperature sensors - which are available in dataviewer, I believe.
For example the temperature sensor nearest ITM X might be Zone 3B sensor 3A.
This lock event shows interesting things. An oscillation in MICH is what eventually unlocks, but (I think) only because at that point the sideband power in the recycling cavity had significantly dropped. As soon as REFL 9I is engaged,there is an oscillation ~ 0.45 Hz showing up in the AS RF45 and 36, and it is clearly visible in the ASAIR RF90 power. The DARM length correction signal shows awful "bursts" at that point.
This is the lock trend I meant to post last night.
