Computational model of collisional-radiative nonequilibrium plasma in an air-driven type laser propulsion

Abstract

A thrust power of a gas‐driven laser‐propulsion system is obtained through interaction with a propellant gas heated by a laser energy. Therefore, understanding the nonequilibrium nature of laser‐produced plasma is essential for increasing available thrust force and for improving energy conversion efficiency from a laser to a propellant gas. In this work, a time‐dependent collisional‐radiative model for air plasma has been developed to study the effects of nonequilibrium atomic and molecular processes on population densities for an air‐driven type laser propulsion. Many elementary processes are considered in the number density range of 1012/cm3≤N≤1019/cm3 and the temperature range of 300 K≤T≤40,000 K. We then compute the unsteady nature of pulsively heated air plasma. When the ionization relaxation time is the same order as the time scale of a heating pulse, the effects of unsteady ionization are important for estimating air plasma states. From parametric computations, we determine the appropriate conditions for the collisional‐radiative steady state, local thermodynamic equilibrium, and corona equilibrium models in that density and temperature range.