As we reported in elog 2046 and 2049, we had issue of filter cavity correction singal drifts. According to the experience of Raffaele, this is due to the tide and can be corrected if we send portion of correction signal to the filter cavity end mirror.

Today I tried to do this, I fed portion of correction signal back to filter cavity end mirror at UTC time 2020-02-20-05:23 and then the correction signal becomes very stable. Up to now, the lock has already lasted for one hour.