AN ULTRA-LOW-NOISE, LOW-FREQUENCY, 6-DEGREES-OF-FREEDOM ACTIVE VIBRATION ISOLATOR

To extend the operating frequency band of earth-based interferometric gravitational wave (GW) detectors down to 1 Hz, an unconventional syst em is required that provides approximately a factor of one million vib ration isolation for the horizontal and more for the vertical, startin g at 1 Hz. To this end, a three-stage ultra-low-noise, high-performanc e active and passive isolation system is being designed and constructe d in order to demonstrate that a high degree of reduction can be achie ved for vibrations at the support points of a GW detector's final pend ulum system. The first stage of this system has been fully characteriz ed and is the main subject of this article. It is an equilateral trian gular platform, 1.1 m on a side, with a total mass of 460 kg, includin g the vacuum system that will contain the other two stages. Active iso lation is achieved by six servocontrol loops, using signals from low-f requency displacement sensors to feed back to noncontacting force tran sducers. The first stage has been actively isolated from vibrations in all six degrees of freedom by at least a factor of 100 at I Hz and ab ove. The system noise limitations at 2 Hz and above are roughly 2x10(- 11) and 5x10(-11) m/root Hz for vertical and horizontal translations, respectively. (C) 1997 American Institute of Physics.