J. Kissel

Following the same procedure outlined in LHO aLOGs 9453 and 9079, I balanced the coils on SUS ITMY UIM/L1, ITMX PUM/L2, and ITMX UIM/L1. The final balanced gains are

             ITMX UIM     ITMY UIM    ITMY PUM
UL            -0.965      -0.997       +1.028
LL            +1.025      +0.976       -0.911
UR            +0.970      +1.019       -1.091
LR            -1.030      -0.998       +0.968

The precision on the ITMX UIM and ITMY PUM numbers is within the usual +/- 0.5%, but for some reason I was able to get a crazy amount of SNR on ITMY UIM, so the numbers are good to with 0.05%. 

This balancing has reduced the L3 P and Y caused by pringle excitation at 4 [Hz] by
Optic    Stage      DOF       Reduction Factor @ 4.0 [Hz]
ITMX      UIM        P               > 24.2 (peak below noise, totally incoherent)            
                     Y               > 1.39 (already balanced well, totally incoherent after balance)

ITMY      PUM        P               25.6 (peak still 95% coherent*)
                     Y               37.4 (peak still 80% coherent*)

ITMY      UIM        P               > 124.2 (peak still 68% coherent, but buried)
                     Y               19. 0 (peak still 90% coherent)

* For ITMY PUM, I could not reduce the Q phases to as small as I normally get, implying there is some other noise contributing to the imbalance unrelated to the knob I'm tuning. Unclear what that could be, but I guess this is why I couldn't reduce the imbalance low enough that the excitation became buried in the noise as I could with the other stages.

I attach the figures of merit for reducing the imbalance. All SUS have had these values captured in there safe.snaps, which have been committed to the repository... except for ITMY PUM which I found not stored while writing this entry. Will store them ASAP.