Spatial Characteristics and Application of Atmospheric Pressure Microwave Nitrogen Plasma Torch

Abstract. Microwave (MW) torches are typically used to produce equilibrium plasmas for various environmental or industrial applications. We use Litmas Red MW torch (2.45 GHz, 3 kW), which is able to generate plasma in a state close to Local Thermodynamic Equilibrium (LTE) in temperature range of 1000-5000 K at atmospheric pressure. We present spatial characteristics of the generated MW plasma and an example of its application. We employ optical emission spectroscopy (OES) as a main diagnostic tool. Thanks to the movement ability of the optical bench we are able to get spectra from various distances from the plasma axis and to analyze horizontal profiles of plasma after Abel inversion. We mostly observed NO, N2 and CN spectra. From the measured and the Abel-inverted horizontal profiles we found out that the emissivity decreases with increasing distance from the plasma axis. Emissivity also decreases with increasing height, but the shape of the profiles is kept. As an example of atmospheric pressure microwave nitrogen plasma application we present the first tests of carbon benefication. The diagnostics of carbon samples was performed by SEM equipped with WDX element analyzer and FTIR spectroscopy. The plasma heat treatment causes a mass loss, a composition change and a structure change of the carbon waste.