After retuning the ISI feedforward controllers (poorly tuned at the first try - https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=6763) and slightly modifying the blend filters, I re-measured the motion of stage 1 and stage 2 in the following configuration:
Stage 1:
- Damping engaged
- Blend at 250mHz with T240 in the super sensor in all DOFs. 2 notch filters were added in CPS low pass complementary filters at 1.05Hz and 3.5Hz
- Isolation level 3 - UGF: 40Hz
- Sensor correction - STS-2 to stage 1 - In X, Y, Z directions
- Feedforward HEPI to stage 1 - X, Y, Z directions
Stage 2
- Damping engaged
- Blend at 250mHz in all DOFs. with and without notch filters. 2 notch filters were added in the CPS low pass complementary filters at 1.05Hz and 3.5Hz
- Isolation level 3 - UGF: 32Hz
- Sensor correction - stage 1 (T240) to stage 2 - In X, Y, Z directions
I have attached spectra of the stage 2 motion in the X&Y and Z directions. Except the at low frequency (below 100mHz), it is within requirements.