Charged particel transport in interstellar plasmas: Improved theory for scattering of cosmic rays in turbulent fields

点击翻译按钮获取中文摘要

Cosmic rays, charged dust particles and turbulent magnetic fields are important constituents of the interstellar medium. Understanding and predicting the transport of charged particles in turbulent media is a key challenge in a number of related disciplines, ranging from magnetic confinement fusion research to astrophysics. In astrophysics, it is the scattering, acceleration and spatial diffusion of cosmic rays in interstellar magnetic fields. The purpose of this proposal is two-fold:First, we want to investigate the transport of fast particles in cosmic magnetic fields, applying scaling concepts which were developed recently in the context of tokamak physics based on the percolation theory. This can be done since although the turbulent scales are extremely different, the scattering mechanisms perpendicular to the background field are basically the same.Secondly, we want to develop an improved weak turbulence transport theory of fast charged particles in a partially turbulent magnetic field, that avoids the usually made quasilinear approximation to the particle orbits, and properly takes into account recent nonlinear improvements. Three statistical properties of the magnetic turbulence are adopted: (1) quasi-stationary turbulence, (2) the existence of a finite turbulence decorrelation time, and (3) spatially homogenous turbulence. In contrast to the scaling theory, weak turbulence transport theories often make use of the Corrsin independence hypothesis allowing one to express a fourth order correlation function in terms of the product of two second order correlation functions. Two central goals of this proposal are (1) the calculation of cosmic ray scattering rates from weak turbulence and scaling transport theories, respectively, and (2) their comparison to verify or disprove the validity of the Corrsin hypothesis for cosmic turbulent magnetic fields. The so improved transport theory will be applied to selected interstellar phenomena such as the diffusive shock acceleration of cosmic ray particles in the presence of large scale parallel spatial gradients of the guide magnetic field.