Maybe the roll mode we're fighting today isn't ETMY after all?
In the attached plot, the traces are 20 min apart, and you can see that the mode we were watching at 13.75 Hz gets bigger. Throughout this time, Rahul was changing setttings on SUS-ETMY_M0_DARM_DAMP_R, trying to get it to stop increasing. However, when the output of the damping filter was a very small number of counts, we weren't really seeing big changes in the slope of the increase in the monitor filter H1:SUS-ROLL_ETMY_RMS_LOG10_OUTMON. When Rahul increased the gain to 1200 (from the original of 40), we started ringing up a different mode quite quickly. That other mode is 13.94 Hz.
13.94 Hz doesn't match any of the roll mode monitor filters we have in place (second attachment) according to the names of the filters. But, maybe this means that ETMY is actually at 13.94 Hz, and some other optic is at 13.75 Hz? Back in July (alog 84982 that Elenna pointed me to), we originally thought that 13.7 Hz was ETMX, but had found at that time that actuating ETMY seemed to improve things.
Anyhow, we may also consider trying to actuate on other optics, to see if we can do anything to that 13.75 Hz mode? While the monitor filters are all quite narrow (as they should be), the actuator filters appear to all be the same between the optics.
Rahul is working to identify which optic this problematic 13.75 Hz mode is, and so has been actuating on ITMY. We're now seeing a mode at 13.87 Hz with the ITMY actuation, so I think ITMY is absolved from being the problematic optic.
Attached plot is during ITMY actuation.
I am able to ring up 13.75 Hz by actuating on ETMX roll - see attached plot.
I was able to ring up this mode and then damp it down using the following settings - FM2+FM3+FM4, Gain -200 (-60 deg phase filter) for ETMX @53W input power. This needs to be checked at higher power and at NLN.
As per Elenna's suggestion - we will start with damping ITMY roll mode first.
ETMY roll mode gain will be set to zero for the next lock.