LIGO Document P070090-x0

Inverted pendulum as low-frequency pre-isolation for advanced gravitational wave detectors

Document #:
LIGO-P070090-x0
Document type:
P - Publications
Abstract:
We have developed advanced seismic attenuation systems for Gravitational Wave (GW) detectors. The design consists of an Inverted Pendulum (IP) holding stages of Geometrical Anti-Spring Filters (GASF) and pendula, which isolate the test mass suspension from ground noise. The ultra-low-frequency IP suppresses the horizontal seismic noise, while the GASF suppresses the vertical ground vibrations. The three legs of the IP are supported by cylindrical maraging steel flexural joints. The IP can be tuned to very low frequencies by carefully adjusting its load. As a best result, we have achieved an ultra low, ∼12mHz pendulum frequency for the system prototype made for Advanced LIGO (Laser Interferometer Gravitational Wave Observatory). The measured quality factor, Q, of this IP, ranging from Q∼2500 (at 0.45 Hz) to Q∼2 (at 12mHz), is compatible with structural damping, and is proportional to the square of the pendulum frequency. Tunable counterweights allow for precise center-of-percussion tuning to achieve the required attenuation up to the first leg internal resonance (∼60Hz for advanced LIGO prototype). All measurements are in good agreement with our analytical models. We therefore expect good attenuation in the low-frequency region, from ∼0.1 to ∼50 Hz, covering the micro-seismic peak. The extremely soft IP requires minimal control force, which simplifies any needed actuation.
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Notes and Changes:

Rev P070090-00-Z:
- Full document number: LIGO-P070090-00-Z
- Author(s): Akiteru Takamori; Peter Raffai; Szabolcs Marka; Riccardo DeSalvo; Virginio Sannibale; Hareem Tariq; A. Bertolini; G. Cella; Nicolas Viboud; Kenji Numata; Ryu Takahashi; Mitsuhiro Fukushima
- Document date: 2007-08-08
- Document received date: 2007-10-30
- Document entry date: 2007-10-30
- Citation reference: Nuclear Instruments and Methods in Physics Research A 582 (2007) 683-692

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