A Nested Inverted Pendulum as a Possible Pre-Isolator for the ET-LF Seismic Isolation System

The third-generation instrument era is approaching, and the Einstein Telescope (ET) giant interferometer is becoming a reality, with the potential to be installed at an underground site where seismic noise is about 100 times lower than at the surface. Moreover, new available technologies and the experience acquired from operating advanced detectors are key to further extending the detection bandwidth down to 2-3 Hz, with the possibility of suspending a cryogenic payload. The New Generation of Super-Attenuator (NGSA) is an R&D project aimed at the improvement of vibration isolation performance for thirrd-generation detectors of gravitational waves, assuming that the present mechanical system adopted for the advanced VIRGO interferometer (second generation) is compliant with a third-generation detector. In this paper, we report the preliminary results obtained from a simulation activity devoted to the characterization of a mechanical system based on a multi-stage pendulum and a double-inverted pendulum in a nested configuration (NIP). The final outcomes provide guidelines for the construction of a reduced-scale prototype to be assembled and tested in the "PLANET" laboratory at INFN Naples, where the multi-stage pendulum-equipped with a new magnetic anti-spring (nMAS)-will be hung from the NIP structure.