Full-wave FEM simulations of electromagnetic waves in strongly magnetized non-homogeneous plasma

Abstract

Electromagnetic wave propagation in anisotropic media has been widely studied over the last decades since there are several applications where anisotropy plays an important role. This paper presents a procedure to carry out three-dimensional (3D) finite element method (FEM) full-wave simulations of the electromagnetic field in inhomogeneous magnetized plasma of an electron cyclotron resonance ion source (ECRIS). We used COMSOL Multiphysics software and MATLAB to model a cold anisotropic magnetized plasma, described by full-3D non-uniform dielectric tensor, enclosed by the metallic cylindrical cavity where the plasma is formed. A proper mesh generation, exploiting FEM-based COMSOL versatility, allowed us to optimally model ECRIS cavity and microwave waveguide launching structure, with a good computational efficiency and high resolution of the solution especially around the resonance regions. Numerical simulations have been performed in the frequency domain: in the resonance regions especially, the material properties exhibit a spatial variation that leads to a large sparse ill-conditioned matrix which is solved by MUltifrontal Massively Parallel Solver (MUMPS) direct method. We implement a method to perform full-wave simulations considering a cold plasma model for the constitutive relations; the obtained results show that the presence of ECR layer, along with the cavity walls, strongly influences the shape and strength of the electromagnetic field distribution, featuring a strong non-uniformity of the main electromagnetic parameters.