When PRMI is locked on REFL 165 I&Q signals MICH rms is dominated by the 60 Hz line and harmonics. It comes from demodulation board.
To increase SNR ZFL-100 LN amplifier (+23.5dB) was installed in LSC analog rack. MICH 60 Hz and harmonics are improved as shown on the plot "mich_err"
I have also added a few resg at low frequencies. MICH rms is not 3*10-10. In Optickle I simulated power dependence in PRC and ARMs on MICH motion. Plot is attached.
I think we need to stabilize MICH even more, down to ~3*10-11 . We can think about increasing RF amplifier gain, modulation index and power on BB PD.
CARM offset reduction was a little better today due to improved MICH RMS. Power in arms increases up to 15 and than starts to oscillate up to 70 and then PRMI looses lock.
Tomorrow we need to discuss where to put RF amplifier. Current design has several drawbacks: