I compared the temp of ETMX IM and TR_IRX in today's data. Obviously, they are related to each other.

During PRFPMI + RF lock, IMC_OUT was around 1.3W. TR_IRX was around 150. So, how much power in one arm ??. 

PRFPMI+RF seemed to be locked from the last night, then the temp of ETMX IM kept increasing. There is no sign to reach saturation at present.

Anyway, we need to take the active balance between the IM heating power to keep ~30K at TM for rejecting N2(?) frosting on the HR surface during lock acquisition and the actual heat-up feature of each TM.

Fig.1 shows one day data on EXC/TMSX vacuum level, ETMX IM temperature and ETMX TM OPLEV length.

Even if the PRFPMI+RF was unlocked and the ETMX IM temperature decreased, the ETMX TM Oplev Len value is increasing. While the vacuum level at EXC and TMSX is improving and recording the ever-best values. 

So, improving the vacuum level can be one of the solutions to defrost H2O?? on windows?

Two days of data from now on the temperature of ETMX IM and WAB.

It shows the temp enhancement of WAB itself when the PRFPMI was locked as ETMX IM. Because WAB is far from ETMX from the point of view of the mechanical contact thermal conduction, this heat up energy may be supplied by the scattered light from the ETMX? 

In contrast with the slow temp enhancement of ETMX IM, the WAB temp shows a quick response with the PRFPMI lock and it reaches the equilibrium temp soon. At least, this means that the thermal anchor for WAB is strong enough. In addition, about 2 hours of oscillation can be found in the WAB temp. At least 8K radiation shield bottom temp did not show such ~2 hours oscillation.

Assuming 1.3W IMC out and 150 buildups for each FP arm cavity, ~ 10kW level intracavity power is expected. However, it is not so easy to estimate the fraction to the scattered light of ~10kW.

Yes, even during cooling of EX payload, the WAB temperature varied with respect to the interferometer lock.

> At least, this means that the thermal anchor for WAB is strong enough.

I would say the lesson learned at the WAB test back to 2016(? I do not remember well...) is well reflected to the current implementation.

> about 2 hours of oscillation can be found in the WAB temp. At least 8K radiation shield bottom temp did not show such ~2 hours oscillation.

This is interesting. why oscillating...??