Quiet Hydraulic Actuators for LIGO

Interferometric gravitational wave detection relies on precisely monitoring the distance between the test masses at the end of each arm which, conveniently, also serve as the end mirrors of the interferometer. For terrestrial detectors, this measurement is corrupted by seismic noise that is several orders of magnitude larger than the anticipated gravitational wave induced motion [1]. To reduce this disturbance and maintain the test mass at its operating point, the test mass is suspended from an alignment and isolation system. This system consists of several stages of isolation to effectively mitigate broadband seismic disturbances (Figure 2). The test mass hangs from a passive pendulum system which is supported by a multistage isolation and alignment system. At the Livingston site, external to the vacuum system, is the pre-isolator system which is intended to suppress large amplitude, low-frequency disturbances and maintain the interferometer at its operating point. This paper focuses on the design of the pre-isolator actuator and the control of the pre-isolator system.