Oli, TJ, Arnaud

We used the earthquake down time opportunity to evaluate safe IMC thresholds for a rung up, in loop CRS. A threshold of 1urad rms at 25mHz seems safe for alerting the seismic nodes to take the CRS out of loop. We will have to verify those thresholds are not too conservative, and that they still work with a full ifo. 

For this test :

HAM2-HAM3 were set to their nominal blends (no sensor correction), and the CRS was put in loop for HAM3. The CRS was rung up to 80 urad pp, 28 urad rms, by flipping the sign of the CRS damping gain. We monitored the IMC stayed locked throughout (fig1). The mode cleaner controls (on MC2) reached at most +/- 50e6 out of the +/- 134e6 limit (less than half the total dac range). In comparison, the Panama earthquake from this afternoon (or the change of ISI state) rung up the CRS to +/- 2.2 urad, 1.5 urad rms (fig2).