Alexa, Evan, Nic, Jeff, Sheila

Today we changed our damping loops for ETMX and ETMY, to be more similiar to the LLO ones (Jeff's alog ).  The power sprectrum for ETMX (M0 damping filters and optical levers)  and ETMY attached.

We started by using filters similar to the Livingston design, and measuring the actuation transfer functions to both the ESD and the UIM. 

We set up the loop so that we think it should be unconditionally stable, and we have been able to get the ugf to 1.5 Hz.  The measurement agrees reasonably well with the model for the open loop. We also made measurements by injecting in the UIM lock filter bank in each arm, which can be compared to the green trace in the plot on the left in the second attachment.  The two arms match each other reasonably, and we think that our cross over is at a lower frequency than we want. 

The gains we have been able to use stably so far are 50 in the DARM filter bank, 0.4 in ETMX L1 locking and 0.67 in ETMY L1 lock, 1 in ETMX L3 lock and 1.12 in ETMY L3 lock. 

It seems like we might need to fix the oscillation in the Y arm before we can move on. 

(This is Sheila, logged in as Alexa)

UPDATED: I have added some pdfs of TFs produced by the models -- AS