Modelling of an argon plasma jet generated by a dc arc

The modelling of a dc plasma source operating at low power and at low mass flow rate is presented. The physical description of the electric arc in volume with chemical and thermal non-equilibrium conditions is given: two-temperature model, ionization-neutralization process and arc-gas interactions are discussed. The modelling assumptions are justified by the local non-dimensional numbers characterizing the system (Damkholer, Reynolds and Knudsen numbers). Special attention is focused on the influence of the arc power on the thermal non-equilibrium between electrons and heavy particles and the resulting ionization rate. The kinetic thermal non-equilibrium is shown as a decreasing function of the arc discharge current and it is established that the electron density never reaches equilibrium conditions, even at the throat exit. Calculations have been performed for a stationary arc confined to the throat. The gas is argon and the flow is axisymmetric and stationary.