Spectroscopic study of a helium microwave discharge produced by the axial injection torch.

This work shows the experimental characterization of a helium atmospheric pressure microwave plasma produced by the Axial Injection Torch (TIA design) at 2.45 GHz. The axial and radial description of the discharge is made under different microwave power and gas flow-rate conditions. For that, the electron and gas temperature and the electron density are determined by using optical spectroscopic diagnostics. The flame produced by the TIA is a non-thermal plasma, which is characterized by electrons with kinetic energies that are much higher than those of the ions, atoms or molecules. Since features of departure from Saha-Boltzmann equilibrium are detected, the possible deviation from equilibrium has been taken into account in order to interpret the results correctly. Specifically, spectroscopic measurements combined with theoretical results obtained by a collisional radiative model were used to determine the radial distribution of the electron temperature and electron density in the flame. As the TIA produces a free expanding plasma, species from the surrounding air enter the discharge. Therefore, a preliminary study of the role of the molecules incoming in the plasma is presented.