  We constructed and operated a double phase (liquid-vapour) pure argon Large
Electron Multiplier Time Projection Chamber (LAr LEM-TPC) with a sensitive area
of 10x10 cm$^2$ and up to 30 cm of drift length. The LEM is a macroscopic hole
electron multiplier built with standard PCB techniques: drifting electrons are
extracted from the liquid to the vapour phase and driven into the holes of the
LEM where the multiplication occurs. Moving charges induce a signal on the
anode and on the LEM electrodes. The orthogonally segmented upper face of the
upper LEM and anode permit the reconstruction of X-Y spatial coordinates of
ionizing events. The detector is equipped with a Photo Multiplier Tube immersed
in liquid for triggering the ionizing events and an argon purification circuit
to ensure long drift paths. Cosmic muon tracks have been recorded and further
characterization of the detector is ongoing. We believe that this proof of
principle represents an important milestone in the realization of very large,
long drift (cost-effective) LAr detectors for next generation neutrino physics
and proton decay experiments, as well as for direct search of Dark Matter with
imaging devices.
