Ryan S, Camilla
Corey 82849, Ryan and I have had some issues with SQZ this morning. Corey adjusted the SHG temp to get enough green power to lock the OPO but after that the SQZ and range was bad. FR3 signal and FC WFS were very noisy.
Ryan tried to take SQZ out, checked OPO temp (fine), reset the SQZ angle from 220deg back to a more sensible 190deg and then put SQZ back in again but he couldn't get the FC to lock. Followed steps in the SQZ wiki to touch up FC1/2 alignment and got H1:SQZ-FC_TRANS_C_LF_OUTPUT to >120, plot. but we still were loosing the FC at TRANSION_TO_IR_LOCKING. THE FC also seemed unstable when locked on green. While we were troubleshooting, the IFO lost lost. Unsure if this is an ASC issue, FC_ASC trends attached (POS for Y and P were moving much more than usual), SQZ ASC trends (ZM4 PIT changes alot).
After the lock loss, the SQZ_FC seemed to lock stably in green with H1:SQZ-FC_TRANS_C_LF_OUTPUT = 160. Plot. This is higher than usual and it's not clear what changed!
Ryan mentioned that something happened to Oli at the weekend where the range was bad but SQZ unlocked and re-locked and it came back good, plot, but this seemed to the the OPO PZT changing to a better place (we know it likes ot be ~90 rather than 50s).
After relocking, everything was fine but the FC ASC wasn't turning on as the threshold was too low, 2.5. Ryan decreased H1:SQZ-FC_ASC_TRIGGER_THRESH_ON from 3.0 to 2.0, this has been slowly decreasing, maybe as we decreased the OPO trans from 80uW to 60uW last week. Plot. Ryan accepted in sdf and then checked SQZ_MANAGER, SQZ_FC, sqzparams to check this isn't set in GRD.
FC ASC lower trigger threshold accepted in SDF. It is not set anywhere by Guardian nor is this model's SAFE.snap table pushed during SDF_REVERT.
After a while, Camilla and I again dropped H1 out of observing as even after thermalization, BNS range and squeezing weren't looking good. We decided to reset the SQZ ASC and angle in case they were set at a bad reference point. I took SQZ_MANAGER to 'RESET_SQZ_ASC_FDS' and adjusted the SQZ angle to optimize DARM and SQZ BLRMS. To reset the angle servo here, I adjusted SQZ-ADF_OMC_TRANS_PHASE to make SQZ-ADF_OMC_TRANS_SQZ_ANG oscillate around 0 (ended with a total change of -10deg), then requested SQZ_MANAGER back to 'FREQ_DEP_SQZ' to turn servos back on, and finally accepted on SDF (attached) to return to observing. It's been about 20 minutes since then, and so far H1 is observing with a much better steady range at around 160Mpc.
What happened that needed the ADF servo setpoint to be updated with a different SQZ angle? Investigation is ongoing.
Attaching the plot from after Corey got the SQZ locked and it was bad, you can see it looks like one of the loops was oscillating, plot attached. Compare to normal SQZ plot.
