Komori, Tanaka

We found that phase margins of the SOFT mode controll, especially Yaw controll, got small. Fig.1-4 show the OLTFs of SOFT mode controll. (Note:Soft mode controll filtters were not changed yet. So the controlls are the same as the O4c ones) 

We considered that the PY coupling in TMS QPDs become larger than before. So we check the PY coupling by injection.

First, we started to check Y2P coupling in CSOFT mode. we injected a 50 mHz sine wave into the loop from the K1:ASC-CSOFT_Y_SM_EXC port and measured the error signal spectra of the CSOFT P and Y respectively. fig. 5 shows the result. The error signal spectra are shown in the left upper panel.  As you can see, 50 mHz peak is in both CSOFT_{P,Y} error even though only Yaw was excited. 

Second, we checked P2Y coupling in CSOFT mode. Fig.6 shows the results. There seems to be 50 mHz peak in CSOFT_P but the peak cannot be seen in CSOFT_Y.  

Similarly, we checked Y2P, P2Y couplings in DSOFT mode. Fig. 7 and Fig. 8 show the results when P and Y was excited, respectively. Like CSOFT mode, Y2P coupling can be seen but P2Y coupling cannot be seen.