SEISMIC VIBRATIONS MECHANICAL FILTERS FOR THE GRAVITATIONAL-WAVES DETECTOR VIRGO

VIRGO is a detector of gravitational waves based on a laser interferom eter with 3 km long arms, now under construction. In order to detect g ravitational waves down to 10 Hz, the seismic noise has to be reduced by several orders of magnitude. New mechanical filters using cantileve r springs as elastic elements have been developed for the VIRGO seismi c isolation system. The spring total stiffness is reduced by more than one order of magnitude using magnetic antispring. A control system al lows one to keep the spring length constant. The new filters provide a n attenuation greater than or equal to 40 dB each for frequencies abov e 10 Hz and, compared to the previously adopted solution (gas springs) , are much less sensitive to temperature changes. (C) 1996 American In stitute of Physics.