Measurement of the transfer function of the steering filter of the Virgo super attenuator suspension

Abstract

The optical elements of the Virgo antenna are supported and isolated from seismic noise disturbances by super attenuator (SA) suspensions. The steering filter (SF) is a component of the SA, designed for the mirror control. The dynamical properties of the SF are described by transfer functions, which have been measured in order to define the control strategy; the results have made it possible to set and tune the parameters of a simulation of the SA. The measuring devices were linear voltage differential transducers: they were found to be quite effective and flexible in usage. An auto-regressive model was used to fit the experimental data, implementing the linear relation between the input forces and the resulting motion. The ability of the model to reproduce the experimental behavior was a clear indication of the good data quality, showing that the contaminating noise was under control. The simulation was able to reproduce the qualitative behavior, and the simulation parameters were estimated, with 10% and 20% accuracy. The estimations were later found to be consistent with the measurements taken on a full SA equipped with the same steering filter. Unknown spectral structures were found only above 20 Hz. (C) 2001 American Institute of Physics

First results of the low frequency facility experiment

“…Regarding the payload (see the payload window in figure 1): one of the mirrors is suspended on-axis in the same way as a VIRGO mirror (VM), from the so-called 'marionetta' [8]. The 'marionetta' is suspended from the last stage of the suspension (the so-called 'steering filter' [9]) by a steel wire in the usual VIRGO way. The second mirror of the FP (auxiliary mirror AM) is suspended off-axis from a steel dummy marionetta.…”

The inertial damping of the VIRGO superattenuator and the residual motion of the mirror

“…The VIRGO target thermal noise [11] has also been plotted in terms of force from the marionette. The slope of the thermal force is positive because, around 10 Hz,ζ m (f ) ∝ f −5/2 (since the pendulum thermal noise dominates in this range), while G(f ) ∝ f −4 (since the mechanical system behaves as a double pendulum [5,12]). Therefore G(f ) ∝ f 3/2 .…”

“…In order to avoid saturation of the readout electronics of the VIRGO interferometer, the tolerable root mean square (rms) motion of the suspended mirrors is ∼10 −12 m. A hierarchical control strategy is needed to cover the entire dynamic range (for a nice introduction to this problem see [2]): feedback forces can be exerted on three points of the SA (the inverted pendulum (IP) [3], the marionette [4,5] and the mirror itself, by means of a recoil mass). The control on the three points is operated in different ranges of frequency and amplitude.…”

Compact vibration isolation and suspension for Australian International Gravitational Observatory: Local control system

“…Control forces are applied indirectly to through a control mass from which the test mass is suspended, in similar fashion to the VIRGO marionetta. 13 In order to provide a flexible platform capable of satisfying the various control requirements, a digital control system was implemented on a Sheldon Instrument digital signal processor ͑DSP͒ board, 14 running on a peripheral component interconnect ͑PCI͒ bus. Each vibration isolator is integrated with an independent digital control system.…”