Tweaked the alignment into the reference cavity. Transmission went from ~1.3 to 4.1.
whilst I was in the enclosure, the HEPA fans and AC tripped off. Don't know why. As a
result it may take the temperature inside the enclosure a while to settle. The pre-modecleaner
heater drive voltage nearing zero was the tell-tale sign that gave it away.
Attached is a plot of the room temperature around the time of the mishap.
is there a new FSS loop measurement to go with this increased cavity power (and increased optical gain)?
as I suspected, the FSS Common gain has not been adjusted to follow the drifting ref cav transmission, so the FSS UGF has been all over the map. Presumably, the transmitted light, which is used for ALS, is also changing by this large factor.
There is something in the reference cavity optical path which drifts way too much. A 1 degF change in the table temperature is making a 2x change in the cavity power.
You can see that Peter's tweak up happens with the temperature high and so the power degrades again as soon as he leaves the PSL and the temperature changes.
The PMC, on the other hand, has almost no temperature dependence to its transmission.
Options:
- Take a couple weeks to diagnose what is wrong with the optical mounts in the refcav path.
- Block the beam to the refcav/FSS as LLO and 40m have done.
- Redesign the FSS & IMC loops to be stable with 3x gain fluctuations.
