Sheila, Jenne, Matt, Stefan, Evan

List of things done today:

• EY L2 now has a rolloff filter (FM7+FM8 in the L2L drivealign) to remove the unwanted L2/L3 crossovers around the violin resonances.
• We switched the BS M2 coil drivers to the low-noise state.
• We spent some time investigating in-vac REFL9 as a CARM sensor:
  • We drove a line into MCL at 48 Hz and then tuned the analog delay line to minimize the apperance of the line in REFL9Q. We found that the best extinction we could get was REFL9Q/REFl9I ≈ 1/5, which seems abysmal.
  • We switched the CARM sensor to REFL9I (settings attached for 23 W operation), but the high frequency DARM noise is worse than with REFLAIR9I.
• We were able to switch control of the common dofs of the test mass ASC into the hard/soft actuation basis (not measured, but calculated from the cavity geometry).
  • This new acutation scheme works fine when engaging the ASC and when powering up (at least to 10 W).
  • The gains of cHard pitch and yaw were adjusted (to -10 and -20 ct/ct, respectively) so that the loops have bandwidths of something like 300­–500 mHz (measured by step response). A bandwidth of 500 mHz will allow us to set reasonable bandwidths for the cSoft loops (perhaps 100 mHz or so?) while still maintaining the appropriate gain hierarchy between the loops. (According to simulation, the hard mode must be suppressed before the transmission QPDs become good error signals for the soft mode.)
• We also looked at the DARM spectrum as a function of DARM offset. Evidently, at lower offsets, the low end of the spectrum improves while the high end gets worse.