Global stability analysis of thermal plasma jets in inductively coupled plasma facilities*

Understanding the hydrodynamic behavior of thermal plasma jets is important in several applications including plasma spray coating, detecting the composition of a chemical solution, and testing thermal protection systems at high temperatures. Of particular interest to us is the plasma jet issuing from an inductively coupled plasma (ICP) torch at the Plasmatron X ICP facility at the University of Illinois Urbana-Champaign. Several experimental campaigns have shown that the hydrodynamics of the jet depend heavily on the operating chamber pressure and input power and, in this work, we describe this behavior from the standpoint of global linear stability. We linearize our finite volume solver about an axisymmetric steady base flow obtained via direct numerical simulation, and we compute the modal and non-modal behavior of the resulting linear operator. Preliminary results suggest that there exist critical pressure and power combinations where the flow transitions from a linearly stable steady solution to an unsteady oscillatory one through a baroclinic torque instability.