Origin and impact of ion heating in the cathode sheath of direct-current argon discharges at moderate pressures

Abstract

In this article, we analyze the impact of ion dynamics in the sheath of argon DC plasma discharges at moderate pressures (13, 65, and 130 Pa), where the ion mean free path is smaller than the sheath width. Our analysis reveals that the evolution of the ion temperature profile plays a major role in regulating the sheath formation process, influencing plasma species density and ion fluid velocity at the cathode. Through meticulous comparison of simulation data from one-dimensional self-consistent fluid models with Particles-In-Cell 1D3V (one dimension in space and three dimensions in velocity) kinetic models, we demonstrate the necessity of considering ion-neutral collisions in fluid models to accurately simulate the glow discharge. In particular, we emphasize the necessity of self-consistent ion temperature profile calculations, particularly in the sheath region. Notably, even at moderate neutral gas pressures, the ion temperature within the cathode sheath can significantly exceed background gas temperature. Kinetic simulations demonstrate the role of ion-neutral collisions in the progressive spreading of ion velocities in directions perpendicular to the cathode sheath electric field.