Arnaud, Alexa, Sheila, Kiwamu,

Tonight we tried closing the ALS diff loop, but it did not go well. We observed a high peak at 1 Hz, which we don't understand and seems to prevent us from going back to the high UGF configuration that we achieved in the last week. Since we ran out our energy at this moment, we will have a close look tomorrow. This may be a gain peaking , a bad cross over or some stupid reason.

We tried increasing the servo gain to the nominal value (which should give a UGF of 4 Hz), but today we were not able to reach that point due to the instability at 1 Hz. So we mostly worked with a lower UGF by a factor of 3 or 4 at which the loop was relatively stable. Changing the TST gain did not seem to help. The attaches s the in-loop error signal (show in red) and free-running noise (in black). When we closed the loop, a oscillation happened at 1 Hz. Hmmmm.....

A good new is that Sheila succeeded in deploying a guardian for the ALS diff control. So it now allows us to keep track of good settings.