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Register a new userGlobal Feed-Forward Vibration Isolation in a km scale Interferometer
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Using a network of seismometers and sets of optimal filters, we implemented a feed-forward control technique to minimize the seismic contribution to multiple interferometric degrees of freedom of the LIGO interferometers. The filters are constructed by using the Levinson-Durbin recursion relation to approximate the optimal Wiener filter. By reducing the RMS of the interferometer feedback signals below sim10 Hz, we have improved the stability and duty cycle of the joint network of gravitational wave detectors. By suppressing the large control forces and mirror motions, we have dramatically reduced the rate of non-Gaussian transients in the gravitational wave signal stream.
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We present a tabletop six-axis vibration isolation system, compatible with Ultra-High Vacuum (UHV), which is actively damped and provides 25 dB of isolation at 10 Hz and 65 dB at 100 Hz. While this isolation platform has been primarily designed to support optics in the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, it is suitable for a variety of applications. The system has been engineered to facilitate the construction and assembly process, while minimizing cost. The platform provides passive isolation for six degrees of freedom using a combination of vertical springs and horizontal pendula. It is instrumented with voice-coil actuators and optical shadow sensors to damp the resonances. All materials are compatible with stringent vacuum requirements. Thanks to its architecture, the systems footprint can be adapted to meet spatial requirements, while maximizing the dimensions of the optical table. Three units are currently operating for LIGO. We present the design of the system, controls principle, and experimental results.
A vibration isolation system called Type-Bp system used for power recycling mirrors has been developed for KAGRA, the interferometric gravitational-wave observatory in Japan. A suspension of the Type-Bp system passively isolates an optic from seismic vibration using three main pendulum stages equipped with two vertical vibration isolation systems. A compact reaction mass around each of the main stages allows for achieving sufficient damping performance with a simple feedback as well as vibration isolation ratio. Three Type-Bp systems were installed in KAGRA, and were proved to satisfy the requirements on the damping performance, and also on estimated residual displacement of the optics.
New generations of gravity wave detectors require unprecedented levels of vibration isolation. This paper presents the final design of the vibration isolation and positioning platform used in Advanced LIGO to support the interferometers core optics. This five-ton two-and-half-meter wide system operates in ultra-high vacuum. It features two stages of isolation mounted in series. The stages are imbricated to reduce the overall height. Each stage provides isolation in all directions of translation and rotation. The system is instrumented with a unique combination of low noise relative and inertial sensors. The active control provides isolation from 0.1 Hz to 30 Hz. It brings the platform motion down to 10^(-11) m/Hz^(0.5) at 1 Hz. Active and passive isolation combine to bring the platform motion below 10^(-12) m/Hz^(0.5) at 10 Hz. The passive isolation lowers the motion below 10^(-13) m/Hz^(0.5) at 100 Hz. The paper describes how the platform has been engineered not only to meet the isolation requirements, but also to permit the construction, testing, and commissioning process of the fifteen units needed for Advanced LIGO observatories.
This paper presents the results of the past seven years of experimental investigation and testing done on the two-stage twelve-axis vibration isolation platform for Advanced LIGO gravity waves observatories. This five-ton two-and-half-meter wide system supports more than a 1000 kg of very sensitive equipment. It provides positioning capability and seismic isolation in all directions of translation and rotation. To meet the very stringent requirements of Advanced LIGO, the system must provide more than three orders of magnitude of isolation over a very large bandwidth. It must bring the motion below 10^(-11) m/(Hz)^0.5 at 1 Hz and 10^(-12) m/(Hz)^0.5 at 10 Hz. A prototype of this system has been built in 2006. It has been extensively tested and analyzed during the following two years. This paper shows how the experimental results obtained with the prototype were used to engineer the final design. It highlights how the engineering solutions implemented not only improved the isolation performance but also greatly simplified the assembly, testing, and commissioning process. During the past two years, five units have been constructed, tested, installed and commissioned at each of the two LIGO observatories. Five other units are being built for an upcoming third observatory. The test results presented show that the system meets the motion requirements, and reach the sensor noise in the control bandwidth.
We present a numerical study on an enhanced periodic auxetic metamaterial. Rotating squares mechanism allied to precompression induced buckling give these elastic structures exotic properties. The static properties of the reference structure and the enhanced ones are first compared. After numerical analysis to ascertain the differences between several band calculation methods, we demonstrate the effect of precompression issued stress field on the dispersion diagram of the metamaterial. An optimization study is then performed to assess the potential vibration isolation improvement obtained with the new design. As a result, the bandgaps widths and range are found to be greatly increased by the geometric modifications proposed.
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