Kinetic Physics of Homogeneous Turbulence in Collisionless Plasmas

University Of California-San Diego, La Jolla CA

Investigators

Abstract

The is a jointly funded project between the National Science Foundation and the Department of Energy. The multi-scale nature of turbulence poses a severe computational challenge for kinetic simulations. This project will aggressively push the limits of full particle simulations of turbulence in plasmas. A recently developed parallel, implicit, full particle kinetic simulation code will be used to perform simulations that will show how long wavelength modes non-linearly cascade to shorter wavelengths. The focus of this project is on the least understood and most controversial aspect of turbulence, namely the transition of long wavelength turbulence to short, kinetic scales and the properties of turbulence at wavelengths shorter than this transition. The goal is to address the physics of how the long wavelength modes cascade from the inertial range to the short wavelength range in the solar wind. The inertial range is fairly well described by single-fluid, magnetohydrodynamic (MHD) models, which have proved to be a very effective approach to describing long-wavelength fluctuations in the solar wind. Observations have shown that the wavenumber at the spectral break, where the inertial range ends, corresponds to the ion inertial length. The ion inertial length marks the breakdown of single fluid theory and kinetic effects become dominant in this regime. As a result, the short wavelength regime has remained the least understood component of solar wind turbulence and many basic questions such as the physics controlling the breakpoint are not completely understood. The proper treatment of the so-called ?dissipation range? requires a fully kinetic treatment. Turbulence is ubiquitous in plasmas, occurring in a variety of settings such as interstellar medium, accretion disks, planetary magnetospheres, and the solar wind. The main theoretical focus has been on long wavelength turbulence where MHD is a good approximation. This project will use a tandem of wave turbulence theory and state-of-the-art full particle kinetic simulations with unmatched computational resources to investigate the evolution of turbulence from the inertial range down to the short wavelength regime characterized by whistler waves. The proposed activity will enhance the infrastructure for research. The project will use cutting edge simulations including cell-based technology to push the limits of full particle-in-cell (PIC) simulations. These advances will pave the way for the plasma physics community to transition to new techniques for simulations using cell-based computers. The codes will be made available through a free GNU General Public License (v2), via the Google Code project. The web site will include not only the code and sample input files, but it also include (i) a brief description of the code and its methods, (ii) a wikipedia-style manual on how to use the code with an extensive description on how to set up a problem and run it, and (iii) sample graphics files to read and plot the results.