Lisa, Rana, Evan, Sheila, Chris, Kiwamu,
The DRMI was stable tonight. So we did several attempts for reducing the CARM offset and the smallest we got tonight was 125 Hz in IR. We will performe careful analysis of lock losses tomorrow.
Lock loss events to lock at are: 7:59:30, 8:11:09 and 8:56 UTC. The second one reached 200 Hz in IR and the last reached 125 Hz. We decreased the MICH gain from 7.9 to 3.0 because its UGF was found to be too high when the arm cavities were held at a off resonant point. According to the lockin demodulators, all the loops stayed without a significant gain change or anything. ALS COMM seemed to tend to lose its lock when it is "IR FINE TUNE". We need to investigate what causes lock losses.
I made an offline analysis of the last lock loss event.
It looks like some kind of instability happened and all the three loops oscillated at 5 or 6 Hz. Since all of them showed similar oscillatory behavior, it is difficult point out which loop was unstable. My guess is that this instability was induced by alignment fluctuation of the DRMI which eventually resulted in a mod hop in SRC -- the hopping-ish events are visible between t= -2.2 and -2.0 where POP18 is glitchy and AS90 went to negative and positive values back and forth. The CARM offset was set to 125 Hz in IR at this time.