Numerical Investigation of the Interaction of an Expanding Plasma Plume with Ambient Gas using Direct Kinetic Simulations

The interaction of a laser pulse with a material surface induces the formation of a plasma plume that expands away from the surface. Understanding laser ablation is key to enhancing the efficiency and performance of pulsed laser deposition, laser propulsion, inertial confinement fusion, and laser-induced breakdown spectroscopy. Such plumes split and sharpen upon interacting with a background gas of intermediate pressure, and a definitive mechanistic explanation remains an active area of research. The highly transient process is amenable to direct numerical simulation, which can probe plume–gas interactions and provide detailed physical insights inaccessible by other means. This requires the adoption of appropriate numerical methods and models. Most studies have employed particle kinetic methods, such as the direct simulation Monte Carlo method, which are subject to statistical noise and are suboptimal for transient flows. Direct kinetic methods solve the Boltzmann equation in an Eulerian fashion and more accurately resolve time-evolving flows. In this work, a direct kinetic solver is used to simulate a two-species mixture as a model problem for laser-induced plume expansion. A weakly ionized plume is initially concentrated at one end of the simulation domain and allowed to expand into ambient low-pressure gas of a distinct species. The roles of key parameters such as the plume–gas pressure ratio and the degree of ionization are investigated, along with sensitivity to underlying collision models.