Kevin, Evan, Elenna, Dan

After the long lock we had at 70W (input to IMC power) last night we tried to push it further today. After fixing some ASC issues (68519) that were causing locklosses about 30 minutes into the lock we decided to try staying at 75W this evening. We found after about 45 minutes some 14Hz buzing in the LSC signals which a few minutes later caused a lockloss. This is due to the factor 4 loss in 9MHz at POP which we are currently not fixing in the guardian, we should comissioning the UGF servo for PRCL. We switched on LSC OSC1 to drive at 245Hz so that we could see how the POP and REFL signal changed over time (From top to bottom, POP9I, POP9Q, REFL9I, REFL9Q, time markers show when we engaged a PRCL bandpass which we forgot to switch on). There is a change in the REFL9 Q signals and a large drop in POP9 I. You can somewhat see REFL9Q starting to rise faster before the T2 marker which also matched with faster changes in some of the ASC offsets, we suspect if we had left it this would have caused a lockloss again. We boosted the PRCL digital gain by 4 and things appeared to level off. We went to nominal low noise and shortly after had a fast lockloss.

We suspect that just bumping up the PRCL gain every power step will probably help a little but the large degradations in the 9 are obviously affecting ASC sensing which will no doubt require tweaking the further we push it but we will try this weekend. I don't expect that the CO2 or ETM RH will help our 9 buildup as it never really fixed it before. Evan tried some PRC2, PRM, PR3 alignment offsets but that did not help.

We are leaving the IFO to lock back up to 70W for the night.