Jenne, Sheila, Kiwamu, Terra, Lisa

We had another long lock at 50W tonight (7 hours so far), and we did several things (list below).

MICH feed forward retuning and IMC WFS offset adjustment had a clear impact on the noise; the IMC WFS offset tuning reduced several peaks in the noise between 500 Hz and 1kHz, and kept the noise above 4 kHz at the minimum. The noise floor is still significantly higher than it should be in the 500Hz-1kHz region, so there is clearly more to do there. Also, unclear at this point how stable these offsets actually are.

Here is the full list of things we did/tried:
Improved MICH subtraction - the best MICH FF gain with the current filters is -15.9 (-13.9 was loaded in the guardian, Jenne updated it) 
IMC WFS offset tuning: Sheila's entry will follow, bottom line is that the noise above 4 kHz is now much more stationary, and we reduced several peaks in the jitter noise between 500 Hz and 1 kHz;
we closed the POP beam diverter (it is still open in normal operation because we are using POPX, we just made a test by opening the ASC POPX loop for a few minutes, from Sep 22, 5.36 UTC to 5.41UTC); we don't think closing the beam diverter made a difference - we opened it again, once we transition to REFL we can close it permanently; 
 we explored different DARM offsets, no real impact on the noise; 
 we run A2L again, it does what is supposed to, but we noticed that the optimal tuning doesn't last long 
 we reduced the ITM ESD bias by a factor of 2 (Sep 22, 5.45  UTC - 5.48 UTC), we didn't see any change in the noise; 
 Jenne explored the dependence of DARM vs OMC alignment by adding offsets to the OMC ASC loops - nothing exciting 
 Terra turned off for a few minutes all the drives for the PIs - no effect on DARM 
 On going: Kiwamu is doing a thermal test by slightly changing the CO2 power - we want to see if we can minimize laser noise couplings this way.
  

Note:  we have a typically big 40.94 Hz ; we found past entries referring to the 40.93 Hz PR2 roll mode; we improved the band stop that it is already in the PR2 M2 actuation path by 40 dB at the exact frequency, but that didn't help; need to follow up on that, the line is big and it is modulated. 

We never had to worry about bounce and roll during the lock, so good job on the tuning  earlier in the afternoon! .