For discussion and pictures of the electrical grounding of the ESD low voltage + high voltage chassis system that was modified today and documented in the above aLOG, check out the original installation in March 2019, LHO:47308, with (just uploaded) pictures of the install from Dec 2019 LHO:64637.

To enhance Fil's words, when he says "removed the removed the dedicated chamber ground to the ESD electronics," he simply disconnected the connection at the beam tube end (shown in this Dec 2019 pic from LHO:64637), bending the stiff low-gauge cable back such that it's literally floating in the air, with the black zip-tie holding it in place so it doesn't wiggle. The connections to the HV and LV chassis remain.

I think it's clear that the grounding cable was doing good things, and I propose we put it back. 

In the attached screenshot today (blue) there is much more noise at 60 Hz + harmonics than Monday (red).  I am comparing guardian state 520 (Max Power), since we have not yet achieved NomLowNoise post-maintenance, but I think it's already clear that we do like having that grounding cable in place.  I wonder a bit if this extra noise is part of the challenge in getting re-locked.  Georgia is going to ask Fil about putting it back after lunch.

I'm not sure that that grounding cable can have anything to do with the different spectrum at high freq, but that would be surprising.  Perhaps this indicates that there's something else also going on that we need to find?  Or, maybe I haven't quite captured the IFO in precisely the same configs on the two days.