Study on the two thermodynamic states of large-scale RF plasma discharge

This study focuses on argon discharge in the inductively coupled plasma (ICP) generator of the Experimental Research Apparatus for Electromagnetic Science of Hypersonic Vehicle Plasma in Near-Space. Discharge models under local thermal equilibrium (LTE) and thermodynamic nonequilibrium (NLTE) conditions are developed to reveal the discharge behavior of a high-power ICP generator under different thermodynamic states. In the LTE model, electrons and heavy particles are assumed to share the same temperature, i.e., the plasma temperature. Compressible turbulent flow is described using the Navier–Stokes equations, and electron density is calculated using the Saha equation. In contrast, the NLTE model assumes different temperatures for electrons and heavy particles. The electron density is obtained by solving the drift–diffusion equation, while heavy particle transport is modeled using a mixture-averaged diffusion coefficient approach. The results show that from the coil region to the outlet, the peak plasma temperature in the LTE model decreases by 6.4%, whereas in the NLTE model, the gas and electron temperatures decrease by 12.7% and 26.2%, respectively. The peak electron density decreases by 42% in the LTE model and by as much as 80% in the NLTE model. Comparison with spectroscopic diagnostic results indicates that the normalized trends of electron temperature and electron density are more consistent with the LTE model predictions. These findings provide theoretical insight for optimizing the design of ICP generators.