Recent progress on the R&D program of the seismic attenuation system (SAS) proposed for the advanced gravitational wave detector, LIGO II

High-performance Seismic Isolation Systems in gravitational wave interferometers are needed not only to increase the sensitivity of the detectors but also to guarantee long periods of stable operation. SAS is essentially a system which produces the required in-band seismic isolation by use of passive mechanical filters and actively reduces the out of band seismic noise using inertial damping. The passive isolation is achieved for all the 6 degrees of freedom, with an Inverted Pendulum and a chain of single wire pendula whose masses are the Geometrical Anti-Spring Filters (GASF). The active control is applied to reduce mainly the noise below 4 Hz and to damp the resonances of the chain acting from the inverted pendulum table. Here we present a brief overview of SAS and recent results achieved from the full scale SAS prototype. (C) 2001 Elsevier Science B.V. All rights reserved.