J. Kissel

Charge measurements have been completed for today. ETMX remains at a low effective bias voltage, though the expected slow-and-steady charge accumulation has begun. ETMY, after last week's single-cycle TMDS discharge use (see LHO aLOG 38524), show consistent *reduced* effective bias voltage, but not nearly as well mitigated as on ETMX with a three cycle discharge. 

It's still most interesting that while ETMX's discharge has drastically reduced the (non-limiting) unexpected ISI ST2 to DARM coupling (see LHO aLOG 38507), ETMY's discharge appears to have reduced *the* mystery noise (LHO aLOG 38540), via unidentified coupling.

Just for ease of "one number reporting" I again take the mean of all pitch and yaw data points, and compute their standard deviation to form a ball-park uncertainty:
         2017-08-31     2017-09-08     2017-09-11    
ETMY      51+/-34        -21+/-12       -22+/-12 
ETMX      -4+/-3          -4+/-3         -4+/-2

Since we're replacing both ETMs in due time, I think we just don't care what the charge is beyond tomorrow, for the forseeable future.
   (a) We know that we can use the TMDS system to discharge an optic at vacuum in ~2 days
   (b) We know we can use the Bias voltage over a long time period to control / minimize the effective bias voltage
   (c) We now will be using conductive gloves in chamber, as well as plenty of dry-N2 gunning.
So may we just take this off our list of things to care about once Post O2 commissioning ceases until a pre-O3 detector begins to appear.

Thanks to T. Vo, T. Shaffer, and J. Warner for running measurements while I was out, see LHO aLOGs 38593 and 38576 for ETMX and ETMY respectively.