Vibration isolation systems for the beam splitter and signal recycling mirrors of the KAGRA gravitational wave detector

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Abstract:: KAGRA is an underground interferometric gravitational wave detector which is currently being commissioned. This device relies on high performance vibration isolation systems for holding its main optical components. These suspensions come in three different configurations, of which the Type-B is used for the beam splitter and signal recycling mirrors. The Type-B suspension comprises the payload, three geometric anti-spring filters for vertical isolation and one inverted pendulum for horizontal isolation. The payload comprises the optic, its marionette and their recoil masses which hold local displacement sensors and coil magnet actuators used for damping the resonant modes of oscillation of the suspension itself. The beam splitter version has a modified lower section to accommodate a wider optic. The payload also relies on an optical lever to monitor the tilt and the longitudinal displacement of the optic from the ground. All four suspensions have now been installed in vacuum chambers. We describe the mechanical, electrical and control design, and the measured performance compared to requirements.

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Notes and Changes:: More corrections to the main text were done and some errors in the author list were corrected. This version will be submitted to Classical and Quantum Gravity.