J. Kissel

As mentioned yesterday/Monday, I fixed a bug that Shivaraj and Saravanan found in the time-dependent correction factor calculations for the optical plant (see LHO aLOG 46260). Woo!
We managed to recover the IFO and hit nominal low noise this evening for about 30 minutes while I was present. Woo!
I was looking around the new system for success, and for about 10 seconds prior to the lock loss, it was all "working" roughly as expected. This time period was surrounding Jan 10 2019 at 01:15:54 UTC -- see attached screenshot of kappa_C, f_C, f_S, and Q_S -- the optical gain, the DARM coupled cavity pole frequency, the detuned signal recycling cavity's optical spring frequency, and its Q.

There still things left to be fixed before it "works" enough to start considering applying these to DELTAL_EXTERNAL:
(1) Obviously, the signs are wrong (negative) on the optical gain (kappa_C) and spring Q (Q_S). This is a problem remaining with the signs of the reproduction of the various reference model parameters (aka "EPICs Records"). These have been created and installed using new(-ish) python code of which all the sign errors have not yet fully shaken out when replicating the current, mixed DARM actuation scheme. Evan and team are still actively working on this (see G1900019).

(2) The gating system (which smoothes out the TDCF for application to DELTAL_EXTERNAL) and override system (which allows us to bypass non-functional parts) don't yet have all settings turned ON in such a way that the relative actuator strength changes -- a.k.a. kappa_UIM, kappa_PUM, and kappa_TST -- are spitting out live values. In this brief moment in time where the optical plant parameters were working, all of the actuator kappas were bypassed and spitting out +1.0.

(3) We're still using a pre-ER13 measurement to determine the DARM loop reference model, which in turn determines the EPICs records, which determine the calculated TDCFs. The actuator measurements were quick and dirty. The IFO was still at 20 watts. Thus -- when I see that the corrective gains, the kappas for both actuator and optical plant, have magnitudes at the 10-30% level, I'm not yet sad. Now that we're electing to stick at 30W input for a while, while we hunt for noise, we should re-take -- or in some cases take for the first time -- quality measurements that will get the system to levels needed for ER14 / O3. 

However, with all the above qualifications -- we made good progress today. We can comfortably (albeit imprecisely) say that the optical gain needs ~10% correction, the DARM coupled cavity pole is at ~420 Hz, the optical spring is at ~15-20 Hz, and the Q is very close to critical at ~1.