Elenna, Camilla, Jenne, Ryan Short, Tony
We saw an increase in the DCPD monitor screen, which the roll monitor identified as ETMX roll mode. The existing settings from a long time ago used AS A YAW to damp roll modes, I attempted to damp this by actuating on ETMY, which seems to have worked with a gain of 20. (settings in screenshot)
Camilla trended the monitor, and sees that this started to ring up slowly around 7 am today.
We've gone back to observing with this gain setting, but we plan to turn it off when this looks well damped (if we are still locked by the end of the eve shift, we should turn it off so the owl operator doesn't get woken up by SDF diffs).
Since we were able to actuate on ETMY, that indicates this is likely the ETMY roll mode. That indicates that either the ASC or the LSC feedforward is driving this mode.
I just took a look at the SRCL feedforward, and I see a pair of high Q zeros/poles (Q ~ 1600!) at about 13.5 Hz that I missed (facepalm). That seems a bit low, since this roll mode appears to be around 13.7 Hz, but we should still remove that anyway. We can take care of this tomorrow during commissioning and that might prevent the driving of this mode.
I can't think of any ASC control that would have a significant drive at 13.7 Hz.
I just removed two high Q features at 6.5 and 13.5 Hz that were in the SRCL feedforward. I kept the same filter but removed the features, so there should be no SDF or guardian changes. My hope is that this will prevent the roll mode from being rung up, so I have turned the gain off and SDFed it. Attached is a screenshot of the SDF change for ETMY roll.
Unfortunately, it appears that the ETMY roll mode is still ringing up, so the SRCL feedforward is not the cause. Another possibility is the ASC. The CHARD P control signal is larger now around 13.7 Hz than it was in April. The attached plot shows a reference trace from April and live trace from last night's lock. I don't know if this is enough to drive this mode. The bounce roll notches are engaged on ETMY L2, and have 40 dB attenuation for the roll mode between 13.4 and 13.7 Hz.
