Abstract:

I implemented GAS modal damping for ETMX as well as ETMY.
It seems to work well.

Detail:

I impelemnted GAS modal damping to ETMX because there is a coherence between TM pitch OpLev signals and GAS LVDT signals.
Figure 1and 2 shows the TF from M1/M2 actuators to M1/M2 sensors, respectively.

Then, I measured the spectrum of GAS filter signals and TM OpLevs (fig3).
RMS of both GAS filters and OpLevs are reduced without inducing the noise at high frequency.
This controls are also implemented into the guardian, so they are automatically turned on at LOCK_ACQUISITION state.