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

A. Takamori, P. Raffai*, S. Márka, R. DeSalvo, V. Sannibale, H. Tariq, A. Bertolini, G. Cella, N. Viboud, K. Numata, R. Takahashi, Mitsuhiro Fukushima

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)


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, ∼12 mHz 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 12 mHz), 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 (∼60 Hz 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 ∼0.1to ∼50 Hz, covering the micro-seismic peak. The extremely soft IP requires minimal control force, which simplifies any needed actuation.

Original languageEnglish
Pages (from-to)683-692
Number of pages10
JournalNuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Issue number2
Publication statusPublished - 2007 Nov 21
Externally publishedYes


  • Gravitational wave
  • Isolation
  • Seismic

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Instrumentation


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