J. Driggers, J. Kissel, T. Sadecki We've been unable to recover further than Corey's last note in his log,LHO aLOG 50772, namely, we've been in 2W DC readout, and begin the power up sequence and lost lock 3 times. We've since gone through an initial alignment -- and been having finnicky, intermittent and thus surpassable issues with ALS_XARM green WFS -- and are now struggling even to recover DRMI, without any knowledge of why. Assuming that some other problem hasn't cropped up, I write the rest of this aLOG assuming we'll just push through these annoying lock-losses and eventually get back to debugging the power up. Jenne and I are running out of steam for today, but we still have a few fox holes to look into. Here're those ideas such that others can continue work. List of current suspects: (1) Alignment looking through the SDF system, there's honestly too much different between the safe.snaps and current EPICs values to understand what's wrong and what's normal. However, one thing that caught our attention was the IMC optic's alignment. Because the IMC was functional after Peter, Niko, and Jason's hard work (see LHO aLOG 50779), Kissel and Corey didn't restore those optics. (2) ISS 2nd Loop The diffracted power is taking quite a dip during IMC lock losses, and we lose lock right at the start of powerup with the full IFO. We should check health / settings of the ISS second loop. The theory being that if the ISS 1st loop is in a bad state / flaky, then the 2nd loop won't work. We know at least that we've gone through initial alignment several times, so we can successfully power up with the 1st loop on, but increase power with the IFO is the first real test of the 2nd loop/ (3) DRMI Buildups trend the POP18 and POP90 values at DC readout (ENGAGE_DC_VIOLINS), see if they're the same as previous successful locks before this morning issues (4) Violin Modes We noticed while in DC readout that ETMY MODEs 1 and 6 were particularly rung up. So, maybe some PD is saturating once we start to increase the power a bit. (5) 9 MHz EOM driver Just looking at the wall FOM for the 9 MHz EOM modulation index driver, it looks a little higher. would be good to compare the current ASD against prior-to-outage ASD.
ISS 2nd loop looks OK to me.
Slow bumping of the diffracted power is the indication that there was a DC change coming from the 2nd loop into the 1st loop board when the 2nd loop was OFF or when it was On but was AC coupled. This happens when turning 2nd loop first, or turning 2nd loop off.
1st loop is extremely slow to respond to this kind of nudging due to that the 2nd loop signal comes downstream of the analog whitening of 1st loop PDs (whitening is built into the 1st loop PDs).
Update: ASC oscillation at 0.55-0.56Hz somewhere (Travis, Keita)
I feel as if ALS is sort of flakey, but once we get passed the stage where we need ALS, we're stable at 2W until ASC slowly starts oscillation at 0.55~0.56Hz.
We lost lock three times due to this when we were trying to damp violin in DC 2W (first attachment).
Third time I reduced the overall ASC gain from 1 to 0.8 to 0.7 or so right before it lost lock, and that made the oscillation somewhat better in e.g. 18MHz buildup peak-to-peak but the IFO lost lock anyway (2nd attachment). It's not clear which DOF is doing a bad thing (maybe MICH_P = AS_A 36Q?).
After the 3rd lock loss from 2W DC, I adjusted dark offset of all AS and REFL WFSs (but actually only RF36 sensors were bad as in dark offsets from Q and I before rotation ~ 50 or so counts).
I need to leave now.