Status Report on Advanced VIRGO
Advanced VIRGO was discussed by Giovanni Losurdo (right). This is an upgrade of the Virgo interferometric detector, participated by France and Italy, the Netherlands, Poland, Hungary and Spain. The long-term goal is to be part of a second-generation detector array. The short-term goal is to join LIGO in the current run this year. Having been funded with two years of delay with respect to the American detectors, Virgo has maintained this delay throughout the data taking.
The main changes with respect to Virgo were a larger beam, heavier mirrors, higher-quality optics, a thermal control of aberrations, an improved vacuum, and others. The first generation detectors ran in the first decade of the 2000’s, not continuously, progressively improving their sensitivity. Virgo ran through 2011, when Ligo was already being decommissioned. The aim of the upgrades was to extend the sensitivity distance by one order of magnitude (as explained previously, these experiments define sensitivity as the maximum distance where they can see a neutron star merger event).
The technology of the mirrors has improved a lot recently, so the residual roughness is of 0.2 nanometers. The coating has also improved. The payload -the final part of the seismic isolation that suspends the mirrors- has been redesigned.
Some problems with the steel wires suspending the masses has been encountered, with some loss of sensitivity. The problem is understood, and right now Virgo is in the commissioning phase. The first milestone is the capability to run stably. The goal is still to join Ligo in the Autumn or Summer.