William D. Dorland
University of Maryland
Small-Scale Electromagnetic Fluctuations in the Solar Wind
I will discuss recent simulations of small amplitude electromagnetic fluctuations in a weakly collisional plasma that is permeated by a magnetic field whose strength is such that the magnetic field energy is comparable to the plasma pressure (beta ~ 1). Such fluctuations have been observed in the solar wind, and are expected in a variety of astrophysical systems. The collisional mean free path in the solar wind is approximately 1 AU, which is much, much greater than the observed fluctuation scales, which can be measured in (hundreds of) kilometers. Transverse to the magnetic field, the observed fluctuation spectra change character when the fluctuation wavelengths are comparable to the proton Larmor radius. Under these conditions (magnetized but weakly collisional), a magnetohydrodynamic description is inadequate. Our theory and simulations are developed in the "gyrokinetic" limit, which has been rigorously derived and explored in the laboratory magnetic confinement fusion program. I will explain what the "gyrokinetic" limit is, present some simulation results and our methodology, compare the simulation results with observations, and discuss the implications of this work.* Questions and discussion are invited.
* G. G. Howes, W. Dorland, et al., PRL, Vol 100, 065004 (2008).