The VIRGO suspensions: design and recent performance measurements

The success of the VIRGO interferometer to detect gravitational waves, starting from a few Hz, depends on the ability of its suspension systems to isolate the test masses from seismic noise and to maintain them actively at a working position with relative displacement of ∼10-12 m rms on a time scale of several hours. For this purpose, considerable development effort has been dedicated to realize a multi-stage vibration isolator to suspend the test masses: the SuperAttenuator (SA). It has been designed to provide an attenuation of more than 10 orders of magnitude starting from about 4 Hz. Hierarchical control forces, exerted via coil-magnet actuators placed at three different stages of the SA, damp the fundamental mechanical modes of the system (all below 2 Hz) and maintain the relative orientation and position of the test mass for interferometer alignment and locking. In this Letter a description of the SA is given and recent experimental results are presented