Vibration isolation systems in adva

Vibration isolation systems in advanced LIGO feature active isolated platforms using various vibration sensors and actuators for feedback and feedforward controls. Figure 2.16 shows schematic and CAD drawings of the vibration isolation systems for the core optics, which are placed inside and around vacuum envelops called the Basic Symmetric Chambers (BSC). Three systems are cascaded to provide up to seven stages of seismic isolation to the core optics; the Hydraulic External Pre-Isolator (HEPI), the Internal Seismic Isolation platform (ISI) and the quadruple pendulum suspension. HEPI and ISI provide precise positioning and active isolation of a suspension platform, from which the core optic is suspended. The platform is isolated from the seismic vibration from low frequency (0.1 Hz) down to the level of ∼ 10 −12 m/ √ Hz at 10 Hz. The seismic isolation systems were installed in the detectors and their robustness and effectiveness have been proved through years of commissioning on the interferometers. The detailed control strategy and measured performance of this active isolation system can be found in reference [49].