Session H20 - Gravitational Radiation - Experiment.
MIXED session, Sunday morning, April 30
102A, LBCC
The frequency band of some interesting and possibly frequent gravitational wave events spans a low frequency range of up to 10 Hz. The main limit in this band is seismic noise, which requires a good isolation system to supress it down to the thermal noise level. We are developing a Seismic Attenuation System (SAS) for LIGOII to realize this low frequency isolation. The SAS, essentially a passive mechanical filter, is designed to provide low frequency isolation starting at 10-100 mHz for all degrees of freedom. The main obstacle for the isolator is to support heavy test masses, while retaining the softness of the system for low frequency attenuation, which is achieved by a Geometric Anti-Spring Filter (GASF) technique. The GASF consists of cantilever blades linked to a load using a geometric anti-spring effect. It can achieve an ultra low resonant frequency (\sim100 mHz), supporting a mass of a few hundred kg. The mechanical setup and materials used are specially selected to reduce creep, excess noise, and high vacuum compatibility. The prototype filters have been fabricated already, and their isolation performance measured. These results would be presented in this talk.