Characterization of transversely confined electron beam-generated plasma using two-dimensional particle-in-cell simulations

Abstract

Electron beam-generated plasmas (EBPs) have been used to modify the surface properties. In certain applications, EBPs are transversely confined and their properties are of value to the treatment. In this paper, the characteristics of an electron beam-generated argon plasma, confined within a narrow gap, are investigated using a two-dimensional particle-in-cell simulation. The employed particle-in-cell/Monte Carlo collision model accounts for the electron and ion kinetics, as well as collisions between electrons and the background gas, including the elastic scattering, excitation, and impact ionization. Our simulations reveal a strong correlation between the plasma density and the beam density within the plasma bulk. The excitation of obliquely growing waves is observed, which is found to have a significant impact on the transport of beam electrons, thereby leading to the non-uniformities of plasma density and electron temperature. Specifically, the obliquely growing waves increase the local plasma density while reducing the electron temperature. These contrasting effects compensate for each other, and therefore, to some extent, smooth out the distributions of ion flux and energy flux. We further examine the variations of plasma parameters with respect to the beam current density, beam energy, and gas pressure. Increasing the beam current density or decreasing the beam energy results in higher plasma density and electron temperature, while increasing pressure leads to a higher plasma density but electron temperature scarcely changes. Based on the simulation results, we propose an approach to achieve independent control of the ion flux and energy flux by adjusting beam current density, beam energy, and pressure.