Electromagnetic coupling dissipation between mirrors and reaction masses in Virgo

We discuss in detail the constraints on the structure of the reaction mass used to control the mirror position in the Virgo interferometer. In particu lar, we present the measurement performed to test the limit imposed by the eddy currents on the pendulum quality factor when the Virgo reaction mass a nd the mirror are coupled by electromagnetic actuators. The low frequency l imits imposed on the sensitivity of the full scale Virgo interferometer are discussed. We conclude that for Virgo a dielectric reference mass should b e used. (C) 1999 Elsevier Science B.V.