A Semi-implicit Particle-in-cell Expanding Box Model Code for Fully Kinetic Simulations of the Expanding Solar Wind Plasma

Abstract

We address the challenges that come with fully kinetic Particle-In-Cell (PIC) simulations of the expanding solar wind by introducing a semi-implicit, Expanding Box Model (EBM) approach to the study of solar wind kinetic physics. Plasma propagation and expansion are dealt with via the variable change of the EBM. In this way the large separation between scales of interest and domain size is addressed by including solar wind propagation and expansion as time-dependent coupling terms and coordinate stretching. The semi-implicit discretization, in the widely used Implicit Moment Method (IMM) flavor, promises to increase the simulated domain size and duration with respect to explicit discretization. The EBM IMM equations are derived and tested against expected behavior of expanding plasma.