Modeling and analysis of a dual channel plasma torch for industrial, space, and launch applications

Abstract

Dual-channel thermal plasma torches can operate with air, argon, or combustible gases to produce high temperature plasma flows. This plasma torch can be used in various important applications such as metal industry recycling, surface coating and hardening, space operations using controlled thrust, and macroparticle acceleration based on the electrothermal nature of thermal torches and electrical-to-thermal energy conversion. Power for this torch is supplied from the electric mains and the voltage is stepped up to 6 kV. However, the torch can also operate in DC or in pulsed mode. The electrical operation is characterized by the VoltAmpere relationship to determine the power rating of the torch and diagnose the dynamic behavior of the plasma. Experiments on the torch using air and argon have shown plasma temperatures of 1 eV and 0.5 eV, respectively, with plasma number densities in the range of 10 24 -10 25 /m 3 , indicating a dense plasma regime with the plasma tending to be weakly nonideal. Plasma kinetic temperature and electron number density were obtained from optical emission spectroscopy using the relative line method as the plasma is near local thermodynamic equilibrium (LTE) condition. The plasma temperature is at a maximum for low flow rates and decreases for increased flow rates. The torch modeling was conducted using an electrothermal plasma code to simulate and predict the parameters for pulsed mode operation. Simulation was conducted on a single channel as the dual torch is symmetric. Code results for extended pulse lengths show a plasma temperature between 0.6 eV and 0.8 eV for nitrogen, oxygen and helium, which are in good correlation with plasma temperatures obtained from optical emission spectra and measured plasma resistivity. A set of computational experiments using short pulses at higher discharge currents have shown temperatures in the range of 2.0-2.5 eV for nitrogen and helium.