A full test of the experimental set-up was foreseen, prior to its final installation at GranSasso. The test run took place in Pavia: the start-up operations begun on April 23rd, 2001.

This detector is essentially a large cryogenics pool equipped with an electronic readout system and it is an ideal device to study particle interaction: it is countinously sensitive, self triggering, cost effective and simple to build in modular form, sufficiently safe to be located underground (no pressure, no fiammable gas, etc.). This detector is also a calorimeter of very large granularity and high accuracy.

The main cryogenic container for the ICARUS 600-ton consists of two semi-independent and symmetric parallelepids of approximately 3.6 by 3.9 by 19.9 cubic meters. Its walls are made of aluminium honeycomb panels. The thermal insulation uses an innovative method requiring no vacuum and based on honeycomb insulating material with cold gas flowing through the cells.The read-out chambers (two TPC for each half-vessel) are mounted on the internal walls with the cathode at the centre, to maximise the LAr sensitive volume (corresponding to about 480 ton in mass).

The read-out chamber scheme consists of three parallel planes of wires (horizontal, +60 and -60 degrees). Information is read both by electric charge induction on the first two readout planes ncountered by drifting electrons and by electric charge collection on the last readout plane. The signals from the three wire planes, together with measurement of the drift time, provide a (redundant) full 3-D image reconstruction of the event. The main features of this type of chamber is that there is no charge amplification in the chamber, to allow the drifting electrons to induce signals on different wire planes. This requires a high quality electronics to maintain a good signal over noise ratio.