P. Puppo

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.

Measurement of the VIRGO superattenuator performance for seismic noise suppression

Below a few tens of hertz interferometric detection of gravitational waves is masked by seismic vibrations of the optical components. In order to isolate the mirrors of the VIRGO interferometer, a sophisticated suspension system, called superattenuator, has been developed. Its working principle is based on a multistage pendulum acting on seismic vibrations as a chain of second order mechanical low-pass filters. A complete superattenuator has been built and tested. This apparatus allows extending the VIRGO detection band down to a few Hz. A detailed description of the attenuation system and its performance are presented in this article.

Suspension last stages for the mirrors of the Virgo interferometric gravitational wave antenna

We describe the design of the last stage suspension for the mirrors of the Virgo gravitational wave detector and, in particular, its key mechanical elements: the marionette and the reaction mass. Since the whole suspension system is an electromechanical device, we present both its mechanical and electromagnetic components. The main features of the fully assembled prototype and those worked out for the Virgo final design are discussed.

The Virgo Project

The Virgo project is a Italian-French collaboration aiming at the construction of a long baseline interferometric antenna for the detection of gravitational radiation signals of cosmic origin. We describe the principles of the system, and high-light the technical challenges we need to overcome for reaching a sensitiity as low as 10−23Hz−1/2.The gravitational clustering of collisionless particles in an expanding universe is modelled using some simple physical ideas. I show that it is possible to understand the nonlinear clustering in terms of three well defined regimes: (1) linear regime; (2) quasilinear regime which is dominated by scale-invariant radial infall and (3) nonlinear regime dominated by nonradial motions and mergers. Modelling each of these regimes separately I show how the nonlinear two point correlation function can be related to the linear correlation function in hierarchical models. This analysis leads to results which are in good agreement with numerical simulations thereby providing an explanation for numerical results. Using this model and some simple extensions, it is possible to understand the transfer of power from large to small scales and the behaviour of higher order correlation functions. The ideas presented here will also serve as a powerful analytical tool to investigate nonlinear clustering in different models.

The VIRGO interferometer for gravitational wave detection.

The Virgo gravitational wave detector is an interferometer with 3 km long arms in construction near Pisa in Italy. The accessible sources at the design sensitivity and main noises are reviewed. Virgo has devoted a significant effort to extend sensitivity to low frequency reaching the strain level h = 10−21 Hz−1/2 at 10 Hz while at 200 Hz h = 3 · 10−23 Hz−1/2. Design choices and status of construction are presented.

Monitoring the acoustic emission of the blades of the mirror suspension for a gravitational wave interferometer

We monitored the acoustic emission activity of the steel blades to be used for the mirror suspension system of a gravitational wave interferometer. We have collected several sets of events getting evidence of a material memory effect (Kaiser effect) associated to the dislocation motion in the steel. This result is more evident when we apply a standard fractal analysis procedure (box counting method) to the timing series of acoustic emission bursts. We conclude that a significant reduction of the emission rate is obtained by applying a few stress cycles to the elastic blades.

Observation of the Brownian motion of a mechanical oscillator by means of a back action evading system

Abstract We present the results of noise measurements performed using a back action evading (BAE) system to detect the random motion of a resonator cooled to 4.2 K. The frequency spectrum of the data shows a peak with bandwidth and amplitude in agreement with the theoretical prediction of the Brownian motion of the resonator. As expected from the theory of BAE transduction, this mechanical signal is present on only one phase of the output and is free from the back action noise of the amplifier.

The Archimedes project: a feasibility study for weighing the vacuum energy

Archimedes is a feasibility study to a future experiment to ascertain the interaction of vacuum fluctuations with gravity. The future experiment should measure the force that the earths gravitational field exerts on a Casimir cavity by using a balance as the small force detector. The Archimedes experiment analizes the important parameters in view of the final measurement and experimentally explores solutions to the most critical problems.

CHARACTERIZATION OF MECHANICAL DISSIPATION SPECTRAL BEHAVIOR USING A GRAVITOMAGNETIC PENDULUM

Abstract We have developed an experimental method based on the reaction of a magnetic mass with respect to a dc biased coil to change the frequency of a pendulum. In a preliminary experiment this method has allowed us to investigate the mechanical dissipation of nylon pendulum wires over the 0.1-1.4 Hz frequency range. According to the procedure shown in this paper, it is possible to deduce from the measurements whether the dissipation process is viscous or not. The method is generally applicable and adaptable to be used to characterise the behaviour of the suspension systems developed for gravitational waves detectors.

Experimental upper limit on the estimated thermal noise at low frequencies in a gravitational wave detector

A. Di Virgilio, L. Barsotti, S. Braccini, C. Bradaschia, G. Cella, V. Dattilo , M. Del Prete, I. Ferrante, F. Fidecaro, I. Fiori, F. Frasconi, A. Gennai, A. Giazotto, P. La Penna, G.Losurdo , E. Majorana, M. Mantovani , F. Paoletti, R. Passaquieti, D. Passuello, F. Piergiovanni, A. Porzio, P. Puppo, F. Raffaelli, P. Rapagnani, F. Ricci, S. Solimeno, G. Vajente, F. Vetrano INFN, Sez. di Pisa, Pisa, Italy 2 EGO, European Gravitational Observatory, Cascina (Pi) 3 Universita’ di Pisa, Italy 4 INFN Sezione di Firenze, Sesto Fiorentino, Italy 5 Università di Roma1, and INFN-Roma1, Roma Italy 6 Universita’ di Siena, Italy 7 Università di Urbino, Urbino, Italy 8 Coherentia, CNR-INFM, and CNISM Unitá di Napoli 9 INFN, Sez. di Napoli, Università di Napoli 10 Scuola Normale Superiore, Pisa