Abstract:

I modified the ASC filters to reduce the residual RMS of effor signals for ARM ASC.
It seems to work well, so I would like to keep IFO in PRFPMI_RF_LOCKED state to check the stability of IFO.

Detail:

As reported in klog35093, ASC loop gain seems to decrease from the nominal value, so I changed the overall gain of ASC by checking WFS error signals.
Based on the measurement in klog35093, I increased the gain of DHARD_P, DHARD_Y, and CHARD_P by a factor of 2 and CHARD_Y by a factor of 1.5.
Gains are set at FM7(6dB), FM3(6dB), and FM7(6dB) for DHARD_P, DHARD_Y, and CHARD_P, respectively.
For CHARD_Y, I modified the FM8 from 3dB gain to 6.5dB gain to increase the CHARD_Y loop gain by a factor of 1.5.

In addition to this, WFS error signals had a large peak at 0.08Hz, so I implemented resG at 0.08Hz with Q=3 and depth =20dB.
These filters are implemented at FM1, FM9, FM1, FM6 of DHARD_P, DHARD_Y, CHARD_P, and CHARD_Y, respectively.
I also tested resG for CSOFT_Y and DSOFT_Y but it doesn't seem to make significant changes, so I turned them off today.

Figure 1 shows the error signals of HARD loops before (blue) and after (red) filter modification.
As you can see, RMS of all error signals are significantly reduced.

I checked if the IFO relock canbe done automaically after my changes and confirmed that it can reach PRFPMI_RF_LOCKED state.
So, I keep this condition tonight and see the long-term stabiity.