Optical characterization of Argon microwave discharge generated at sub-atmospheric pressure.
Résumé
Microwave Plasma Torch (MPT) are used since several decades as a efficient system to generate a
plasma medium of high energy density with elevated thermal and active species fluxes. The
evaluation of the operating parameters influence on the plasma parameters, namely electrons
density and temperature, remains a decisive task in order to optimize the working operation of
MPT.
The current experimental investigations address the characterization by means of standard optical
techniques of a regular MPT operating with Argon at sub-atmospheric pressure (1-100 mbar). Here,
the optical techniques have been specifically setup to record the light intensity coming from the
Argon plasma discharge, i.e. from the region where the plasma absorbs the transmitted microwave
power. The excitation temperature has been determined by means of Optical Emission
Spectroscopy (OES) technique at low resolution. The analysis of the distribution of population
density among excited energy levels has been conducted for a broad range of working conditions.
Evidences for a clear departure to equilibrium distribution has been obtained confirming the
ionizing plasma situation. Complementary high-speed imaging measurements have
been conducted to identify the features of the spatial extent of the discharge which exhibits a
specific morphology within the covered pressure range.