Aritomi, Tanaka
We performed some trials, mainly transition from 1f to 3f. But the trial was not work. We need more investigation.
### DRMI lock modification
This morning, DRMI lock got unstable for some reasons. One reason is that MICH loop is oscillated at SRM ADS frequency: ~6 Hz. At that moment, we were not sure of the cause of the oscillation. At once, we turned off only SRM ADS. Also, we changed the setpoints. Then, DRMI lock became stable a little. Another reason is that sometimes PRCL began the oscillation at ~100 Hz. After DRMI lock becoming stable a little, we measued the OLTFs. PRCL UGF increased to 100 Hz though the phase margin was less than 10 deg. So we lowered the gain. Similarly, SRCL OLTF seems to get better. We adjusted the gain. Current SRCL UGF is ~60 Hz (fig.1), PRCL UGF is ~40 Hz (fig.2).
Finally, the gains of the loop summerized the FM4 filter.
### Trial of the transition from 1f to 3f
To transit to 3f signal, we performed the phasing of 3f signals. we followed the procedure in klog32604. As for PRCL, we performed the phasing for REFL135 PD to maximize the I signal when PRCL was excited(fig.3). As for SRCL, we performed the phasing for REFL51 PD to maximize the I signal when SRCL was excited (fig.4). After that, we checked the RF51 signal when MICH was excited. Although the demod. phase is optimized for the SRCL signal, I signal was larger than Q signal when MICH was excited because BS motion is mixture with common and differential length change (fig.5). So we may need to decouple each motion. However, this time, we proceeded our work with this state.
We measued each relative gain and phase between 1f and 3f signals. the figures in the right lower 2 panes of fig. 3, 4, and 5 show each gain and phase of PRCL, SRCL, and MICH. As you can see, the relative phase of SRCL and PRCL seems to be 180 deg. But, the phase of MICH is 40 deg since there are some couplings. Anyway, we input these values in matrix (fig.6) and tried the transition. Then we succeeded PRCL and SRCL transition but failed MICH transition. So we moved the decoupling.
To decouple the DoFs, we excited the one DoFs, PRCL (left panel in fig.1) or SRCL (left panel in fig.2) and measued the relative gain and phase of between excited DoF error signal and others' error signal. From the results, I chosed CARM_IN1 as decoupled sensor for MICH 3F for the test, XARM_IN1 as decoupled SRCL 3F, and YARM_IN1 as decoupled PRCL 3F. After the decoupling, I measured the coupling but the ratio seems not to changed.
### DRMI ADS modification
This morning, we also found that DRMI began the oscillation at ~6 Hz just after engaging ADS. 6.3 Hz is the dither frequency of SRM YAW. The resG for SRM ADS in the MICH loop caused the oscillation. After decoupling the 1f error signals, MICH OLTF seems to got better than before. According to the MICH loop, current MICH UGF is around 10 Hz (fig.6). So I turned off the resG filter in engaging ADS. Then, ADSs seem to become stable.
### DRMI alignment Implementation to the INITIAL_ALIGNMENT guardian
After the modification of DRMI ADS, I implemented the DRMI alignment state with DRMI_1F_LOCKED into the INITIAL_ALIGNMENT guardian. I have not checked INITIAL_ALIGNMENT guardian behavior due to the earthquake.
