Progress and Challenges in Kinetic Plasma Modeling for High Power Microwave Devices

We review progress in kinetic plasma modeling by electromagnetic particle-in-cell (EM-PIC) algorithms on unstructured grids. These algorithms are implemented in modular CONPIC and BORPIC C++ codes which integrate a matrix-free explicit finite-element (FE) Maxwell solver based on a parallel sparse-approximate inverse (SPAI) algorithm and a first-principles charge-conserving scatter algorithm to transfer charged particle information into dynamic variables on the grid. The Maxwell solver of the EM-PIC algorithm utilizes a mixed FE basis and discretizes the time-dependent coupled first-order Maxwell's system explicitly. The explicit solver approximates the inverse FE system matrix (“mass” matrix) using hierarchical sparsity patterns based on the sparsity pattern of the original matrix. The resulting algorithm effectively accounts for multiscale plasma phenomena. We discuss the application of the developed EM-PIC algorithm to the analysis of laboratory plasmas, vacuum electronic devices for generation of high power microwave signals, and RF electronics multipactor effects in harsh space environments.