The Virgo automatic alignment system

The automatic alignment system of the Virgo interferometer differs substantially from those used in similar experiments, since it uses a variant of the Anderson technique. This implies a completely different control topology with respect to other detectors, and the main feature is a strong coupling of different degrees of freedom in the optical signals. It also provides two extra output ports in which differential wave-front sensors can be placed, namely the light transmitted by the Fabry-Perot arm cavities. We report on the first experimental demonstration of this technique on a large scale recycled interferometer, and on the present status of the automatic alignment system.