AURIGA: the suspensions


The tiny bar vibration induced by a passing g.w. is easily masked not only by the thermal noise (thus making the bar cooling a necessity) but also by the mechanical and acoustical noises. The acoustical noise coming from the laboratory environment is suppressed by placing the bar in a vacuum chamber: in AURIGA two vacuum chambers (the OVC and the IVC that houses the bar) provides for this insulation.

A more difficult task is to reduce the mechanical noise: this is due to floor vibrations, caused for instance by any nearby moving vehicle or walking person and by the intrinsic seismic noise. The AURIGA cryostat is placed on the top of a special platform, separated from the rest of the laboratory. The platform sits on a sand layer which reduces by 20dB the mechanical noise at the floor: this is measured to be **** around the AURIBA bar resonant frequency (which occurs at 920 Hz). Unfortunately this noise level is still too high for a g.w. experiment as AURIGA. 

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