F. Marion

The Virgo interferometer

The Virgo gravitational wave detector is an interferometer with 3 km long arms in construction near Pisa to be commissioned in the year 2000. Virgo has been designed to achieve a strain sensitivity of a few times at 200 Hz. A large effort has gone into the conception of the mirror suspension system, which is expected to reduce noise to the level of at 10 Hz. The expected signals and main sources of noise are briefly discussed; the choices made are illustrated together with the present status of the experiment.

Status of the VIRGO experiment

The VIRGO experiment was approved in September 1993. The goal of the French-Italian collaboration is to detect gravitational waves using a 3 km arm-length Michelson interferometer. The construction of this detector, which will be installed in Pisa, is under way. The experiment is planned to take data, in a large bandwidth (10 Hz-10 kHz), at the beginning of the year 2000 with nominal sensitivity close to h = 3 X 10-‘3/&. The motivations, detection principle, main sources of noise and status of the experiment are presented.

A VME BASED CCD IMAGING SYSTEM FOR THE VIRGO INTERFEROMETER CONTROL

Abstract Large interferometric detectors, like VIRGO, are planned to detect gravitational waves, by observing the motions of the suspended mirrors of a Michelson interferometer with kilometric Fabry Perot cavity arms. Due to the large sensitivity needed, the set-up requires a real time monitoring of its mirrors positions, and the analysis of beam shape during the alignment. In this paper, we present the development and the performance of a beam imaging system which uses a CCD camera interfaced to a VME board.

VEGA, AN ENVIRONMENT FOR GRAVITATIONAL WAVES DATA ANALYSIS

A new generation of large scale and complex Gravitational Wave detectors is building up. They will produce big amount of data and will require intensive and specific interactive/batch data analysis. We will present VEGA, a framework for such data analysis, based on ROOT. VEGA uses the Frame format defined as standard by GW groups around the world. Furthermore, new tools are developed in order to facilitate data access and manipulation, as well as interface with existing algorithms. VEGA is currently evaluated by the VIRGO experiment.

A camera based position control of a suspended optical bench used in a gravitational wave detector

The VIRGO gravitational wave detector uses several optical benches suspended inside a large vacuum system. One of these benches is placed at the interferometer output port and it includes all of the optics required to collect and filter the interferometer dark fringe beam. The position of this bench is controlled with respect to ground by means of a charge coupled device camera and 400 light-emitting diodes placed outside the vacuum tank. The read-out sensitivity is a few 10−8 m/√Hz for the translations degrees of freedom and 10−7 rad/√Hz for the rotational degrees of freedom. Displacements as large as ±10 mm and rotations at the level of ±5 mrad can be measured. The feedback is based on a digital architecture and it has been fully tested at the VIRGO site. It is able to control all the six degrees of freedom of the bench with a precision better than 1 μm for the translations and 0.5 μrad for all the rotations.

A SIMULATION PROGRAM FOR THE VIRGO EXPERIMENT

Within the VIRGO experiment we are developing a simulation program providing an accurate description of the interferometric antenna behaviour, taking into account all sources of noise. Besides its future use as a tool for data analysis and for the commissioning of the apparatus, the simulation helps finalizing the design of the detector. Emphasis is put at the present time on the study of the stability of optical components implied in the global feedback control system of the interferometer.

Photodiodes selection for the VIRGO detector the first step

Abstract In the framework of the gravitational waves detector VIRGO, we are developing the photo detectors system. The diodes we will use must satisfy at the same time quite unusual criteria, among them a good quantum efficiency at a wavelength of 1.06 μm and a good linearity at MHz frequencies for an incident light power of 100 mW. We present here the test method and the first very promising results we obtained towards these directions with commercially available diodes in InGaAs.

H∞ Control of a Gravitational Wave Detector Using Normalized Coprime Factor Plant Descriptions

Abstract This paper deals with large-scale gravitational-wave detector control. These detectors use multiple optical cavities and require a coherent control of several suspended mirror positions. In fact the mirrors forming the detector are oscillating around their equilibrium positions under the influence of the earth seismic noise. Hence a control system is needed in order to control the mirror positions at a certain precision level specified by the detection sensitivity. We present in this paper a H ∞ control approach of the detector, based on the H ∞ loop shaping design method of Glover and Mc-Farlane (D.McFarlane and K.Glover, 1992). The design method is first discussed and then the simulation results, obtained with the suspension simulation program, are commented.