[Yokogawa, Sugimoto, Enomoto]
(Yesterday work)

We implemented and engaged the temperature loop of PLL X, and succeeded.
The following time series plot shows how it woks; after it is engaged, the feedback signal of PLL (Ch1, red one) fluctuates around zero and does not show much drift.

Thanks to this temp loop, PLL had been kept for more than 30 mins until main laser went wrong due to lock loss of RefCav, so it was not our fault

= The loop topology =
It is so simple. The feedback signal of PLL, slow output of PLL common mode servo, is regarded as error signal, and then fed back to PROMETHEUS temperature controller.
The filter is a lowpass filter that has one pole at 1mHz and DC gain of -0.05. Targeted UGF (cross over frequency) is 0.1Hz.