Daniel, Sheila, Evan

Summary

Over the past 45 days, we had two instances where the common-mode length control on the end-station HEPIs hit the 250 µm software limiter. One of these events seems to have resulted in a lockloss.

Details

The attached trends show the ISC drives to the HEPIs, the IMC-F control signal, and the IMC-F offloading to the suspension UIMs over the past 45 days. One can see two saturation events: one on 25 September, and another on 11 October.

We survived the event on 11 October: the EY HEPI hit the rail, and counts began to accumulate on the EY UIM, but the control signal turned around and HEPI came away from the rail. On the 25th of September, both end-station HEPIs hit the rail, and after about 2 hours of counts accumulating on the UIMs, IMC-F ran away (second attachment). Note that both HEPI drives started at 0 µm at the beginning of the lock stretch.