A control strategy for seismic noise reduction on advanced LIGO gravitational-wave detector

The differential seismic motion between the internal seismic isolation platforms on the advanced laser interferometer gravitational wave observatory, affects the sensitivity of the detector at lower frequencies (below 1 Hz), because each platform moves independently. This induces noise inside the cavities of the auxiliary optics placed on the platforms, which translates into a higher control effort to maintain stability and resonance. This paper shows that the differential motion between the platforms can be efficiently measured by the capacitive position sensors installed on each platform. We investigate how we can use these sensors to modify the seismic control configuration and help reduce the differential motion between the platforms, reduce the control efforts and help maintain the cavities in resonance. Reduced differential motion is expected to reduce control noise thereby improving sensitivity and improve detector duty cycle by preventing actuator saturation, resulting in loss of optical cavity resonance.