Abstract:

I tuned PRC ASC and it seems to work well now, at least short term.
To check the long-term stability, I will keep PRFPMI_RF_LOCKED state today.

Detail:

As reported in klog35355, I investigated ASC.

First, I checked the phasing of REFL RF45 signals by injecting 13.125Hz sine signals from PRCL error point.
To avoid the unwanted coupling from DARM and MICH, I added resonant gain at FM4 of DARM2 and MICH1, which was enabled during the measurement.
Phasing seems fine except for REFL QPD1 RF45 SEG1, so I only change REFL RF45 QPD1 SEG1 phase from 68.396 to 108.396 (40 deg rotation).
Figure 1 shows the spectra of each segment after phasing, and all I signals have larger signals than Q signals.

Then, I measured the spectrum of REFL 17/45 QPD1/2 PIT/YAW and POP 17 QPD1/2 PIT/YAW signals to check which signals can detect each suspension motion largely.
Following tables are the rough summary of the measured data (original data can be found at /users/Commissioning/data/ASC/2025/1024/ with the file name of WFS_*).

Above values are the TF measurement from oplev signals of each suspensions when exciting to each WFS signals.
For PIT, REFL_QPDA2_RF17_I is not decoupled well for IMMT2 and PR3 but I ignored it because PR3 ASC gain is much higher than that of IMMT2, which reduce the effect of coupling.
For YAW, REFL_QPDA1_RF45_I is not decoupled well for PR3 and BS, so I decoupled it by adding REFL_QPDA1_RF45_Q signals to I signals.

Based on these measurement, I set the matrix element for PRC1 as shown in fig1 (PIT) and 2 (YAW).
The absolute value of the matrix element was decided so that the WFS signals are roughly calibrated in the unit of urad of PR3 angular motioin.
I also set the output matrix element from ORC1 to PR3 as shown in fig3 and 4.

Then, I modified the filter bank of PRC1_{P,Y} to achieve the 0.6Hz UGF loops for PRC ASC as shown fig 5 (FM1,2,3 was added for adjusting gain and the others were not changed because the integrator was already implemented).

After the ASC tuning, ASC seems stable at least for a short term.
So, I will keep IFO in PRFPMI_RF_LOCKED state to check the stability of new ASC loop.