Betsy, Sheila, Travis, Evan
Something about the following coils appears to be unhealthy: PRM M1 RT&SD, PR3 M1 T1&T2. See attached OSEM sensor spectra.
According to Betsy, this high-frequency junk started around 2015-08-29 15:00:00 Z. On the control side, this junk dominates the rms of the PRM M1 LF drive (it is about 10000 ct).
Probably this is related to the problem that Kiwamu saw last night with PRM M1 DAMP L.
The first plot below is a trend of PRM DAMP L showing the start of the noise - the noise started in the middle of the lock stretch from Sat morning. The second plot shows the 4 OSEM Sensors - it's hard to see it in any of the sensor trends, except PRM RT.
For Richard: yes, all 4 of these noisy signals are on the same cable set and Sat box line.
It looks like this high-frequency noise is due to the shadow sensors. We paused in LOCK_DRMI_1F with the PRM aligned, and turned off the top stage damping. In this state there were no digital signals going to the coil driver (MASTER_OUTs were zero), and the NOISEMON and FAST_IMON readbacks were flat. But the inputs from the RT and SD OSEMs had the high-frequency noise. See attached spectra. So, it doesn't look like it's a bad coil driver (this would have been three in as many weeks)...maybe it's an issue with the satellite box?
With the top stage damping enabled, the noise is large enough that it passes through the damping filters and shakes the M1 stage, but it's so high frequency that I don't think we are shaking the optic. There's no sign of the noise peaks in the PRCL error signal. No reason to think we can't run like this until Tuesday maintenance.
We have seen this before at LLO back in July 2011: https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=1262