Sheila, Craig

CARM UGF ~ 22 kHz, Phase Margin ~ 45 degrees
IMC UGF ~ 100 kHz, Phase Margin ~ 25 degrees

Today we worked on locking the interferometer (surprise).

We increased the gains on the IMC servo board inputs by 8 dB each, increasing the UGF from 36 kHz to above 100 kHz.

TR_CARM gain was increased to 2, then decreased back to 1 as this was causing gain peaking at 500 Hz in CARM when lowering the offset.

START_TR_CARM has been improved so we no longer lose lock or saturate SRM.

When we reach RESONANCE, things are pretty wobbly according to the AS AIR camera and our PR_GAIN calculation.  We can improve this by engaging FM3 in DHARD_P and increase the gain to -30.

We increased the analog CARM loop gain by a factor of ten (it used to be ~ 2kHz) to allow us to engage the Common servo board compensation boost in the CARM_TO_ANALOG state.  We did this by increasing the REFL9I summing board gain to 23 dB.  In O2 it was 8 dB, and last night it was 14 dB. 

POP sensors were phased for DRMI (POP 45 to minimize SRCL in Q).  We then measured TFs between the REFLAIR 3f PDs and the POP 1f PDs, found a POP 1f sensing matrix relative to the REFLAIR 3f one, then switched DRMI to POP control.  The POP 1f sensing matrix has been touted as "pretty similar to O2" by Sheila.  Pics below.  The new values are in the guardian, loop measurements are attached for PRCL and SRCL.  We were manually stepping through the rest of the DRMI_ON_POP guardian state when we lost lock probably for unrelated reasons. 

Buildups were slightly worse today (TR_X_NORM ~ 930, implying a PR gain of about 28).

We were locked on CARM_TO_ANALOG for over an hour (August 7, 2018 6:30:00 to 7:39:00 UTC) while we did this, very stable even without ASC (except for DHARD_WFS and occasional BS touches).