Simulations of cosmic ray propagation

TL;DR

This paper reviews numerical methods for simulating cosmic ray propagation, including phenomenological and self-consistent models that incorporate complex physical processes and are used to interpret observational data and understand galactic evolution.

Contribution

It introduces advanced algorithms for kinetic cosmic ray propagation models, integrating MHD and particle evolution for the first time in a comprehensive manner.

Findings

Development of algorithms for CR propagation in kinetic models

Application of models to galactic wind and magnetic field amplification

Insights into cosmic ray influence on galactic evolution

Abstract

We review numerical methods for simulations of cosmic ray (CR) propagation on galactic and larger scales. We present the development of algorithms designed for phenomenological and self-consistent models of CR propagation in kinetic description based on numerical solutions of the Fokker-Planck equation. The phenomenological models assume a stationary structure of the galactic interstellar medium and incorporate diffusion of particles in physical and momentum space together with advection, spallation, production of secondaries and various radiation mechanisms. The self-consistent propagation models of CRs include the dynamical coupling of the CR population to the thermal plasma. The CR transport equation is discretized and solved numerically together with the set of magneto-hydrodynamic (MHD) equations in various approaches treating the CR population as a separate relativistic fluid within the two-fluid approach or as a spectrally resolved population of particles evolving in physical and momentum space. The relevant processes incorporated in self-consistent models include advection, diffusion and streaming well as adiabatic compression and several radiative loss mechanisms. We discuss applications of the numerical models for the interpretation of CR data collected by various instruments. We present example models of astrophysical processes influencing galactic evolution such as galactic winds, the amplification of large-scale magnetic fields and instabilities of the interstellar medium.