Seismic Attenuation Technology for the Advanced Virgo Gravitational Wave Detector

The current interferometric gravitational wave detectors are being upgraded to what are termed ‘second generation’ devices. Sensitivities will be increased by an order of magnitude and these new instruments are expected to uncover the field of gravitational astronomy. A main challenge in this endeavor is the mitigation of noise induced by seismic motion. Detailed studies with Virgo show that seismic noise can be reinjected into the dark fringe signal. For example, laser beam jitter and backscattered light limit the sensitivity of the interferometer. Here, we focus on seismic attenuators based on compact inverted pendulums in combination with geometric anti-prings to obtain 40 dB of attenuation above 4 Hz in six degrees of freedom. Low frequency resonances (< 0.5 Hz) are damped by using a control system based on input from LVDTs and geophones. Such systems are under development for the seismic attenuation of optical benches operated both in air and vacuum. The design and realization of the seismic attenuation system for the Virgo external injection bench, including its control scheme, will be discussed and stand-alone performance presented.