  ICARUS T600 liquid argon time projection chamber is the first large mass
electronic detector of a new generation able to combine the imaging
capabilities of the old bubble chambers with the excellent calorimetric energy
measurement. After the three months demonstration run on surface in Pavia
during 2001, the T600 cryogenic plant was significantly revised, in terms of
reliability and safety, in view of its long-term operation in an underground
environment. The T600 detector was activated in Hall B of the INFN Gran Sasso
Laboratory during Spring 2010, where it was operated without interruption for
about three years, taking data exposed to the CERN to Gran Sasso long baseline
neutrino beam and cosmic rays. In this paper the T600 cryogenic plant is
described in detail together with the commissioning procedures that lead to the
successful operation of the detector shortly after the end of the filling with
liquid Argon. Overall plant performance and stability during the long-term
underground operation are discussed. Finally, the decommissioning procedures,
carried out about six months after the end of the CNGS neutrino beam operation,
are reported.
