Sheila, Evan, Koji

• Tonight evan spent some more time on damping the 1stharmonic violin modes, more details coming later.  
• Several times today we increased the recycling gain by moving the ITMs in pitch (most moving ITMX down in PITCH), and each time we lost the lock.  Twice we were adjusting the alingment slowly, things seemed stable and we had sudden lock losses, April 16 22:05:49 UTC and April 17 8:42:35.  In both of these cases the ASC MICH P loop starts to have problems before the lockloss, although there isn't an oscialltion that grows, and there doesn't seem to be a satration in the suspension until after the problem has already started.  A next step to understanding why we are unstable with a recycling gain above 30 might be to make a good emasurement of the MICH ASC loops.  
• We have spent some more time looking at the noise that is contaminating the spectrum from 100- 50 Hz, which has been coming and going today.  We think that part of the story is as Gabriele suggested, (17912) SRCL noise which has a non stationary coupling that could be realted to dETM motion, or at least is predicted well by the AS45I YAW signal.  Evan and Gabriele added a more agreesive boost to DHARD YAW, which is not turned on by the guardian, which supresses motion in DHARD yaw, but does not make the SRCL coupling at 90 Hz stationary.  We also tried adding a bandstop to the SRCL loop around 100 Hz, this does not change the level of noise, so it seems that this mechanism can't expalin all of the non stationary noise we are seeing.  We also tried adding an offset to the DHARD YAW error point, by doing this we were able to make the noise a bit worse.  We would like to double check the phasing of the ASA 45 WFS.
• We measured the coupling from PRCL noise to DARM using a white noise excitation.  At 50 Hz this is approximately at the level of 3e-20, it should not be the limiting noise in DARM anywhere but now we can add it to the noise budget.