Simulationen zur Untersuchung nichtlinearer Diffusion in vorgegebener und selbstgenerierter Turbulenz
Final Report Abstract
The heliosphere and the interstellar medium are filled by very energetic charged particles (mainly protons). These particles are not stopped by collisions, but they interact with the magnetic field that is permeating the interplanetary and interstellar medium. These magnetic field are highly turbulent and the interaction with the particles is, therefore, a very complicated process. Within this project we tried to identify the main transport processes by combining the simulations of magnetised fluids (MHD) and particles. The project was divided into two halves: One was focussing on the evolution of turbulence in MHD fluids itself, while the other half was devoted to the actual transport of the charged particles. In the field of turbulence evolution it was investigated, how anisotropy is forming in a magnetised, turbulent fluid and how the turbulence initiated by a particle beam is evolving and dissolving. Important results were a detailed discussion of the evolution of turbulence in magnetised fluids and the exploration of the effect of pseudo-Alfvén waves on the transport of charged particles. The understanding of plasma turbulence evolution is of importance since many physical systems - not only the ones studied here - are turbulent and turbulence plays an important role in the way they work. While turbulence is itself important, the understanding is, due to the nonlinear nature of turbulence, still. Plasma turbulence is a very important field of study, since turbulence is present in many systems and is also a crucial element in the physical processes of these systems. Since turbulence is a strongly nonlinear phenomenon, our understanding of it is still very poor. We probed a specific parameter range for turbulence, where different mechanisms of evolution could be verified and the theory of Goldreich & Sridhar was recovered. This research helps in understanding also satellite observations, which may cover only small parts of the turbulence regime. From this point on test particles were used to test the transport of particles. Here a method was used, that produces a more realistic physical scenario, which is on the other hand numerically far more expensive. Using this method previous results could be recovered, while additionally resonant interaction with so-called pseudo-Alfvén waves could be detected. This allows for changes of the transport of particles moving perpendicular to the magnetic field. During the project we discovered that the actual quantities used to describe particle transport were only poorly defined for real particles in real turbulence, since they were only valid for the quasilinear approximation. We tried to overcome this problem by a set of newly derived analysis techniques for particle distributions moving in turbulent magnetic fields.
Publications
- “Simulation of Charged Particle Diffusion in MHD plasmas”, ASTRA, 7, 2011
Spanier & Wisniewski
- “Diffusion of Energetic Particles in Turbulent Magnetohydrodynamic Plasmas”, Astrophysical Journal, 750, 2012
Spanier & Kissmann
(See online at https://doi.org/10.1088/0004-637X/750/2/150) - “Evolution of plasma turbulence excited with particle beams”, Astronomy&Astrophysics, 546, 2012
Lange & Spanier
(See online at https://doi.org/10.1051/0004-6361/201219579) - “Semi-analytical model of cosmic ray electron transport”, ASTRA, 7, 2012
Ivascenko & Spanier
- “Particle scattering in turbulent plasmas with amplified wave modes”, Astronomy&Astrophysics, 553, 2013
Lange, Spanier, Battarbee, Vainio & Laitinen
(See online at https://doi.org/10.1051/0004-6361/201220804) - “Turbulence evolution in MHD plasmas”, Journal of Plasma Physics, Volume 79, Issue 5, pp. 597-612, 2013
M Wisniewski, R Kissmann, F Spanier
(See online at https://doi.org/10.1017/S0022377813000147)
