After the SR3 heater test last night seemed to improve our range, we were curious if the big effect really was thermal, or if it was alignment. With the SR3 heater on to 5, SR3 had moved about 5 urad in pitch, and since we were locked last night, the rest of the SRC ASC followed along. This evening, without the SR3 heater, we moved SR3 to the oplev values that it went to last night due to the wire heating. There was no real effect on the interferometer, which isn't too surprising since Anamaria reminds us that SR3 and SR2 are pretty degenerate.
On the way, there were some places that perhaps seemed a little bit better for the HWS clipping on a baffle, so SR3 is currently back to its slider value in yaw, and almost back in pit. Notably, for when we do the SRC alignment offsets, making the SRC2 yaw inmon negative seemed to roughly correspond to better range, although there were enough things moving around and converging that I can't promise this is repeatable. But, it's at least a direction to start in for this test we already wanted to do.
The first figure is a set of spectra with yellow as the nominal SR3 position reference, Gray is after I had moved in pitch (which was a lot), and red is after I had also moved in yaw (which was not a lot). You can see that for the most part there is no difference, except a bit above the ADS lines near ~25 Hz. The nominal pitch position was better than the candidate position.
The second figure is a set of time series from the start of my moves through the end. You can see that the DARM cavity pole increased a little bit with the pitch moves, and the kappa_c went down a very small amount. The third figure is a zoom of my way back, showing that perhaps we got some better range while the yaw loops were trying to catch up.
Overall conclusion: The improvement from the SR3 heater test last night must have been from the actual thermal effects, not alignment. Next to try is engaging the old SR3 pitch cage servo to keep the M3 OSEM angular readbacks constant while the heater is turned on.
