Filamentary magnetohydrodynamic plasmas

Abstract

We develop a filamentary construct of magnetohydrodynamical plasma dynamics based on the Elsasser variables. This approach is modeled after discrete vortex models of hydrodynamicai turbulence, which cannot be expected in general to produce results identical to ones based on a Fourier decomposition of the fields. La a highly intermittent plasma, the induction force is small compared to the convective motion, and when this force is neglected, the plasma vortex system is described by a Hamiltonian. For a system with many such vortices, we present a statistical treatment of a collection of discrete current-vorticity concentrations. Canonical and microcanonical statistical calculations show that both the vorticity and the current spectra are peaked at long wavelengths, and the expected states revert to known hydrodynamical states as the magnetic field vanishes. These results differ from previous Fourier-based statistical theories, but it is found that when the filament calculation is expanded to include the inductive force, the results approach the Fourier equilibria in the low-temperature limit, and the previous Hamiltonian plasma vortex results in the high-temperature limit. Numerical simulations of a large number of filaments are carried out and support the theory. A three-dimensional vortex model is outlined as weil, which is also Hamiltonian when the inductive force is neglected. A statistical calculi_tion in the canonical ensemble l lnstitute for Fusion Studies,

Fluctuations associated with a filamentary density depletion

“…It is becoming more apparent that microscopic filamentary structures [1][2][3][4] are a fundamental feature of magnetized plasmas that are far from thermal equilibrium. Magnetic field-aligned filamentary structures can consist of density depletions or enhancements, localized pressure changes, current channels, charged flux tubes, or combinations thereof, depending upon the specific boundary conditions and sources that drive the plasma away from thermal equilibrium.…”

Dynamics of narrow electron streams in magnetized plasmas

“…A stream is considered narrow if its transverse dimension is on the order of the larger of the electron skin-depth (c/ pe , where c is the speed of light and pe is the electron plasma frequency) or the ion gyroradius. This situation may be encountered in magnetic reconnection studies [1], dynamo models [2,3], satellite and rocket observations of depleted flux tubes in the auroral ionosphere [4,5], structured small-scale Alfven waves, and laboratory studies of striation formation. The low frequency (below the ion cyclotron frequency, i Ω < ω ) parallel electric fields associated with these environments are capable of producing large parallel drifts, v D , in the electron distribution function that are unstable to high frequency electrostatic modes (in the LH range).…”

Properties of drift waves in a filamentary density depletion

“…The broader interest in exploring the properties of drift waves in microscopic filaments is that, increasingly, it is being recognized [5][6][7][8][9][10][11] that filamentary structures are a fundamental feature of magnetized plasmas that are far from thermal equilibrium. Specifically, density depletions of the type investigated in this study have been observed in widely different environments including ionospheric heating experiments, 12 in situ measurements of the auroral iono-sphere by rockets 13 and spacecraft, 14 and in radar and rocket studies 15 of the equatorial F region.…”