Transport of Cosmic Rays in the Universe

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To explore the interaction between energetic particles and magnetized plasmas is important in astrophysics and space science. Plasmas can be found everywhere in the universe ranging from the solar wind plasma to the interstellar and extragalactic medium. Electrically charged particles, such as cosmic rays, experience scattering if moving through the plasma due to the interaction with turbulent magnetic fields. Therefore, the particles move diffusively and a simple calculation of particle trajectories is no longer possible. Understanding the diffusion process is relevant in order to understand the propagation but also diffusive shock acceleration of cosmic rays. The latter mechanism is responsible for the creation of cosmic particles and it was mentioned in the literature that to understand the origin of cosmic rays is one of the most important problems in the physics of the 21st century. In order to explore particle diffusion one can use two different tools. In analytical theory one combines fundamental equations with different assumptions and approximations. Eventually one finds analytical forms for diffusion coefficients describing the motion of the particles. Such forms can then be used in studies of space weather, cosmic ray propagation, and diffusive shock acceleration. The second tool is provided by test-particle simulations. Due to the increase of computing power in the late 20th and early 21st centuries, one can now solve the Newton-Lorentz equation for an individual particle numerically. By repeating this approach for thousands of test-particles, one can obtain diffusion parameters from such simulations. Both approaches have their advantages and disadvantages but they also complement each other. My group uses both tools, analytical theory to improve our understanding of the transport and to obtain formulas which can be used in different applications, as well as simulations to obtain diffusion parameters with high accuracy. To explore the interaction between energetic particles and plasmas is not just important for improving our understanding of fundamental processes in the universe. Diffusion theory results are also relevant for space weather investigations. To predict cosmic radiation intensities will be important for manned missions to Mars in the future but also to prevent the failure of technical equipment on Earth as well as satellites. For Canada, as a northern country, this is in particular important. Furthermore, the more fundamental aspect of our work is also relevant for optimizing fusion devices such as tokamaks. The goal of the proposed work is to improve our understanding of how energetic particles interact with astrophysical plasmas by using sophisticated analytical and numerical tools. We consider different applications with the aim to explain measured cosmic ray spectra and different observations in the solar system as well as in our own and external galaxies.