[Aritomi, Yuhang, Yaochin]

First we checked CC2 correction signal. Correction signal is 8.2 Vpp (Pic. 1). As you can see from the picture, it is saturating. This may be saturation of servo.

Then we injected this correction signal to ADC CH13 directly and tried to feedback to input test mass. We just set the gain -0.5 for filter. Surprisingly, the test mass feedback worked well without any filter. Pic. 2 shows CC2 correction signal when gain is 0 (blue), -0.5 (green), -1 (red). CC2 correction signal is suppressed when the loop is closed. CC2 control is more or less stable with test mass feedback now. We will improve CC2 with proper filter. Pic. 3 is CC2 in loop phase noise when CC2 is stable with test mass feedback (CC2 error signal is 56.4 mVpp). Note that free running phase noise and in loop phase noise are measured at different day. Turbo pump was ON.