Kevin, Matt, Sheila, Elenna, Corey

After yesterday's ETMY RH change to avoid the 10kHz PI 85514, we lost lock 3 times overnight due to 80kHz PIs.

Apartently the RH change also changed a violin mode damping phase for ETMY 1 kHz mode (mode 20 1000.307 Hz), 85526, which did not cause the earlier locklosses but is growing to the point where it is dominating the DCPD RMS in this lock, but responded well the Elenna's sign flip.

Kevin took a look at the 10kHz higher order modes, second attachment.  The top panel shows how the higher order modes have been thermalizing before the ring heater change, the bottom panel shows three locks since the ring heater change which is a few minutes before 2 hours into the lock, so these can be compared to the green trace in the top panel. THe x arm higher order modes are sitting around 10.6kHz at this point in the self heating thermalization, the yarm modes were below the scale on this plot before the change and are now moving up to around 10480Hz.   If they gain another 20Hz as the self heating kept thermalizing similar to the x arm, this would have put them around 10500 Hz which doesn't have a lot of accoustic modes visible here. 

We don't want to revert the ring heater change from last night as that setting had the y arm sitting right below the forest of accoustic modes.  Matt estimates that we could move the y arm below this forest of accostic modes by going to 1.5 or 1.6W per segment, but that would mean that our two arm modes are more different from each other.  First we tried lowering the power a little more, to 0.9W per segment to see if that helps the 80 Hz modes.  Then Matt estiamted that we could put the Y arm 2nd order mode in a similar location to the x arm by using 0.6W per segment, so we've now set them to that.

Matt took a reference here before the PI rang up, it looks like the PI is 80297 Hz, I got a reference that includes the peak and the lockloss transient, which shows the frequency as 80298 Hz. The signal used for the PI damping is DCPDs downconverted at 80kHz, with a bandpass that goes from 294 to 298.5 Hz, so our peak is within the bandpass. The PLL set frequency is 299Hz, we lowered this 297.5Hz. It was being sent to ETMX for damping, which did appear to work once but not as the mode grew.  We think this is a y arm PI, since we have been changing the Y arm ring heaters, so I've changed the output matrix to send this to ETMY.