Test particle simulations of cosmic rays. (arXiv:1910.01172v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Mertsch_P/0/1/0/all/0/1">Philipp Mertsch</a> (Aachen)
Modelling of cosmic ray transport and interpretation of cosmic ray data
ultimately rely on a solid understanding of the interactions of charged
particles with turbulent magnetic fields. The paradigm over the last 50 years
has been the so-called quasi-linear theory, despite some well-known issues. In
the absence of a widely accepted extension of quasi-linear theory,
wave-particle interactions must also be studied in numerical simulations where
the equations of motion are directly solved in a realisation of the turbulent
magnetic field. The applications of such test particle simulations of cosmic
rays are manifold: testing transport theories, computing parameters like
diffusion coefficients or making predictions for phenomena beyond standard
quasi-linear theory, e.g. for cosmic ray small-scale anisotropies. In this
review, we seek to give a low-level introduction to test particle simulations
of cosmic rays, enabling readers to run their own test particle simulations. We
start with a review of quasi-linear theory, highlighting some of its issues and
suggested extensions. Next, we summarise the state-of-the-art in test particle
simulations and give concrete recipes for generating synthetic turbulence. We
present a couple of examples for applications of such simulations and comment
on an important conceptual detail in the backtracking of particles.
Modelling of cosmic ray transport and interpretation of cosmic ray data
ultimately rely on a solid understanding of the interactions of charged
particles with turbulent magnetic fields. The paradigm over the last 50 years
has been the so-called quasi-linear theory, despite some well-known issues. In
the absence of a widely accepted extension of quasi-linear theory,
wave-particle interactions must also be studied in numerical simulations where
the equations of motion are directly solved in a realisation of the turbulent
magnetic field. The applications of such test particle simulations of cosmic
rays are manifold: testing transport theories, computing parameters like
diffusion coefficients or making predictions for phenomena beyond standard
quasi-linear theory, e.g. for cosmic ray small-scale anisotropies. In this
review, we seek to give a low-level introduction to test particle simulations
of cosmic rays, enabling readers to run their own test particle simulations. We
start with a review of quasi-linear theory, highlighting some of its issues and
suggested extensions. Next, we summarise the state-of-the-art in test particle
simulations and give concrete recipes for generating synthetic turbulence. We
present a couple of examples for applications of such simulations and comment
on an important conceptual detail in the backtracking of particles.
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