A compact triaxial active vibration isolator for cryogenic suspended interferometry

Suspended interferometry at cryogenic temperatures down to 10–20 K requires conductive cooling in addition to radiative cooling techniques, which is challenging due to vibrations emanating from the ground and direct force perturbations from the cryogenic system potentially acting back on the seismically isolated mirrors. In this work, the passive and active isolation performance of a triaxial cryogenic active vibration isolator designed to operate at temperatures below 10 K and ultra-high vacuum conditions with pressures below 10−9 mbar is investigated. While passive isolation of ground motion is effective for frequencies above 6.5 Hz, active suppression of motion and force disturbances can be achieved between 2.46 Hz and 21.4 Hz leading to a reduction of root-mean-square motion by one order of magnitude in the active control band. The performance limits of the current system are evaluated and compared with requirements of ETpathfinder, a prototype facility for investigating cryogenic technologies that enable the target low-frequency sensitivity improvement of the planned Einstein Telescope compared to current terrestrial gravitational-wave detectors.