New generation of Superattenuator for Einstein Telescope: preliminary studies

Seismic noise and local disturbances are dominant noise sources for ground-based Gravitational Waves detectors in the low frequency region (0.1 to 10 Hz) limiting their sensitivity and duty cycle. With the introduction of high-performance seismic isolation systems based on mechanical pendula, the 2nd generation laser interferometric detectors have reached the scientific goal of the first direct observation of GW signals thanks to the extension of the detection bandwidth down to 10 Hz. Now, the 3rd generation instrument era is approaching, and the Einstein Telescope giant interferometer is becoming a reality with the possibility to install the detector in an underground site where seismic noise is 100 times smaller than on surface. Moreover, new available technologies as well as the experience acquired in operating advanced detectors are key points to further extend the detection bandwidth down to 2 Hz with the possibility to suspend cryogenic payload and then mitigating Thermal Noise too. Here, we present a preliminary study devoted to improving seismic attenuation performance of the Advanced VIRGO Superattenuator in the low frequency region of about five orders of magnitude. Particular care has been carried on in analyzing the possibility to improve the vertical attenuation performance with a multi-stage pendulum chain equipped with magnetic anti-springs that is hung to a double Inverted Pendulum in nested configuration. The feedback control requirements and possible strategies to be adopted for this last element will be presented.