Jenne, Evan, Terra, Sheila

Now that we are locking at least on RF, here is a summary of some of the problems we had and things we changed. It seems clear that the MICH ASC loop was not working well with the old TCS settings, and that changing TCS helped (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=29097).  The other significant changes we made in the last few hours that may havbe helped with locking were reverting the MICH ugf for 3F to the old value (unclear), and commenting out the CARM gain redsitrbution.

CARM gain redistribution

We commented out the CARM gain redistribution from the ANALOG CARM state today.  This gain redistribution was intended to keep the sliders all at positive gains for noise performance, but we saw that after the gain was resditributed we had large glitches in the MC2 drive.  These large glitches were not present before the vent, and are gone now that we have commented this out.'

The first attached screenshot shows that on August 1st, the drive to MC2 did not change much after we went through analog carm, but that over the weekend it was much noisier after we went through Analog CARM. The next screenshot shows the glitches showing up as we do the gain redistribution, and in the last one the analog  carm state has completed without large glitches once the gain redistribution is commented out. 

It might be good to swap out the common mode board, in case the problem is that some gain slider which used to work no longer works. 

DHARD gain peaking

Once we locked, we saw a a verry narrow line at 9.45 Hx once the ASC came on, which was due to gain peaking in DHARD.  The only change we know of to this loop was correcting the mistake in the notches for ETMX However, this bounce/roll notch is the same as the one that has been in use for all the other test masses.  For now we have commented out the gain increase in DHARD in the REFL POP WFS state, but we know that this will not be stable for powering up, so we will need to fix this.

We were able to engage the rest of the ASC except the soft loops, which have large offsets and cause the interferometer to move too fast for the SRM dither loop to keep up.  This is probably because our green reference changed. 

To summarize changes that we made over the last several days of trying to lock:

Changes that might matter:

• TCS change
• commenting out CARM gain redistribution
• increasing the MICH gain in 3F by a factor of 2, then reduced it back to the normal gain
• Moving the Yarm green camera reference
• ETMX bounce roll notch engaged, DHARD gain reduced (this will prevent powering up until fixed).
• POP A yaw offset added

Changes that shouldn't have mattered:

• SR3 moved, and moved back
• BS oplev glitching and temporary fix by turning up current
• DRMI ASC engaging change in the order (may have been needed because of bad TCS)
• accidental bounce mode damping gain increases commented out of gaurdian.
• HAM6 ISI changes

Things that we still need to fix:

• common mode board gain sliders
• large soft offsets may need to be adjusted
• DHARD loop shape not stable with notches correctly engaged, low bandwdith not stable for powering up
• OMC problem that Evan will write about