Last night we had a lot of troubles in closing the ASC loops in DRMI configuration, just after we tried to move by hand SR2. Basically, the MICH loop has a large offset.
One of the suspects is that we ended up in a different alignment condition for the SRC that might cause a bad behavior of MICH error signal, even though we don't have any good explanation.
I looked into the SR2, SRM and BS positions during all our DRMI locks. In the two attached plots, the top panel shows the relevant DRMI powers, and the bottom panel the local sensors for the mentioned optics. All signals have been rescaled arbitrarly to fit into the plot.
From the first plot we can see that:
- Before time ~8 h, everything is working fine, and we could close MICH, PRC1, PRC2 and INP1 loops, improving the build ups.
- The lock loss at about time 8 h is caused by our trial to move SR2 and see what happens to the WFS signals
- After that, MICH is no more working
- The local sensor signals are quite reliable on a time scale of few hours (no major drifts)
The second plot is a zoom of the last four hours, when we were having ASC troubles. It seems to me that in all those trials, we never really reverted the SR2 position to its original value (blue trace in the bottom plot). So my guess is that we were in a different alignment configuration for the SRC, and this might explain our problems (we know that the MICH error signal is strongly coupled to SRC dofs)
