After resetting all ISI and suspensions to a working state, aligning the IFO and spending two hours to gte DRMI to lock despite a good alignment, I could retuned the P2L of all test masses. I first tried to inject some DHARD_P noise and tune all four gains, but this didn't work out very well.
So I injected noise on the L2_LOCK_P channel of each test mass indipendently, and tuned the P2L gain. The one that got changed most is ETMY (it was compeltely wrong, sign included).
The table below show the old and new values
| Old | New | |
|---|---|---|
| ITMX | 1.848 | 1.850 |
| ITMY | 0.945 | 1.050 |
| ETMX | 1.269 | 1.200 |
| ETMY | 0.433 | -0.090 |
The attached plot shows the transfer function from DHARD_P (measured with noise) before and after. The coupling is reduced by aboput 15 dB above 14 Hz. A bit less below, as usual due to the phase rotation created by the roll mode band stops. In the plot, the two DARM spectra are both with noise injection, same amplitude.
