Modeling of non-equilibrium effects in inductively coupled plasma discharges

The extreme heat loads imposed on a thermal protection shield during hypersonic re-entry are often reproduced by placing a sample of a thermal protection material in a hot jet of plasma. An important class of plasma wind tunnels is the ICP (inductively coupled plasma) facility which offers a large volume of contamination-free plasma for a considerable amount of time as it does not require electrodes to generate the plasma. An important aspect in the modeling of ICPs is the possible impact of Non-Local Thermodynamic Equilibrium (NLTE) effects. Most of the ICP studies reported in the literature assume that LTE conditions prevail. This assumption, however, breaks down at low pressures due to lowering of collisional rates among gas particles. Under these circumstances, the availability of accurate NLTE kinetics models is of paramount importance.

The present work investigates on the study of non-equilibrium effects in inductively coupled plasmas (ICP) using state-of-the-art multi-physics computational framework developed at the Center for Hypersonics and Entry System Studies at UIUC. The framework couples a plasma solver with an electromagnetic solver to model the magneto-hydrodynamics in the ICP facility. Simulations performed using 2-T NLTE model reveals significant non-equilibrium effect in the ICP torch. Further, investigations using state-of-the-art collisional radiative (CR) models show non-Boltzmann population distribution of the internal states (e.g. electronic and vibrational states) of the species. Capturing these NLTE effects are of utmost importance for accurate modeling of the ICP facility experiments as well as in understanding the dynamics of plasma inside the ICP torch.