One of the fundamental waves in magnetized plasmas is the shear Alfven wave. This wave is responsible for rearranging current systems and, in fact all low frequency currents in magnetized plasmas are shear waves. It has become apparent that Alfven waves are important in a wide variety of physical environments. Shear waves of various forms have been a topic of experimental research for more than fifteen years in the large plasma device (LAPD) at UCLA. The waves were first studied in both the kinetic and inertial regimes when excited by fluctuating currents with transverse dimension on the order of the collisionless skin depth. Theory and experiment on wave propagation in these regimes is presented, and the morphology of the wave is illustrated to be dependent on the generation mechanism. Three-dimensional currents associated with the waves have been mapped. The ion motion, which closes the current across the magnetic field, has been studied using laser induced fluorescence. The wave propagation in inhomogeneous magnetic fields and density gradients is presented as well as effects of collisions and reflections from boundaries. Reflections may result in Alfvenic field line resonances and in the right conditions maser action. The waves occur spontaneously on temperature and density gradients as hybrids with drift waves. These have been seen to affect cross-field heat and plasma transport. Although the waves are easily launched with antennas, they may also be generated by secondary processes, such as Cherenkov radiation. This is the case when intense shear Alfven waves in a background magnetoplasma are produced by an exploding laser-produced plasma. Time varying magnetic flux ropes can be considered to be low frequency shear waves. Studies of the interaction of multiple ropes and the link between magnetic field line reconnection and rope dynamics are revealed. This manuscript gives us an overview of the major results from these experiments and provides a modern prospective for the earlier studies of shear Alfven waves.

The many faces of shear Alfvén wavesa)

Trapping (capture) into resonance and scattering on resonance: Summary of results for space plasma systems

Experimental results on current-driven turbulence in plasmas - a survey

Dispersion curves are plotted for the extraordinary branch of the electron- and ion-cyclotron harmonic waves propagating perpendicularly to the static magnetic field in a non-relativistic, hot Maxwellian plasma, without invoking the electrostatic approximation. It is found that, except in the vicinity of the cyclotron harmonics and the hybrid resonances, either the cold-plasma or the electrostatic approximation are accurate representations of the exact solution. The hybrid resonances of the cold-plasma model become monotonically shrinking regions of low group velocity as the temperature is increased, till all discernible evidence of these resonances disappears as the parameters corresponding to the thermonuclear plasmas are approached.

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Dispersion Curves for the Generalized Bernstein Modes

¯ e/2. The wave thus propagates from a region where Landau damping is significant to where ion-cyclotron damping dominates. Detailed two dimensional measurements of the wave magnetic field morphology are presented. The measured wavelength decreases in accord with WKB solutions of a modified wave equation. Wave damping is also observed and dissipation by both ions and electrons is required in the WKB model to fit the data. Suppression of the damping via electrons in the model results in a predicted wave magnetic field amplitude twenty times larger at the ion-cyclotron resonance point than observed. © 2001 American Institute of Physics. @DOI: 10.1063/1.1389092#

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Shear Alfvén waves in a magnetic beach and the roles of electron and ion damping

Skin Effect and Anomalous Resistivity Accompanying Turbulent Heating

rf PLASMA HEATING IN A MIRROR MACHINE AT FREQUENCIES NEAR THE ION CYCLOTRON FREQUENCY AND ITS HARMONICS.

Radio frequency heating at powers up to 1 MW and pulse widths of ∼700 μsec was applied to a turbulently preheated hydrogen plasma in a large pulsed mirror machine. Energy analysis of charge exchange neutrals indicates that resonant heating occurred when the radio frequency matched either the ion cyclotron frequency or one of its harmonics. The behavior of the induced rf fluctuations in the plasma was observed by means of microwave scattering. These measurements show resonance phenomena and the presence of rf fluctuations at harmonics of the rf heating frequency. Diamagnetic loop measurements indicate that 310 ≤ (Te+Ti) ≤ 380 eV as a result of the heating, while measurements of the ion energy distribution by charge exchange energy analysis shows the ion energy distribution to be non‐Maxwellian with a low temperature component of Ti ∼ 320 eV. Microwave interferometer measurements indicate densities of ∼2 to 3 × 1013 cm−3.

High power fundamental and harmonic resonant ion cyclotron heating in a mirror machine

Parametric Study of Turbulent Heating in a Linear Discharge

Multichannel neutral atom energy spectrometers for energies of 0.3-10 keV for use on fast pulsed plasma experiments are described. The spectrometers consist of a gas stripping cell, a fixed or variable magnetic prism, and a row of scintillator-photomultiplier detectors. Calibration, data analysis, and some operating experience are described.

S. Robertson

Papers

Skin Effect and Anomalous Resistivity Accompanying Turbulent Heating

rf PLASMA HEATING IN A MIRROR MACHINE AT FREQUENCIES NEAR THE ION CYCLOTRON FREQUENCY AND ITS HARMONICS.

High power fundamental and harmonic resonant ion cyclotron heating in a mirror machine

Parametric Study of Turbulent Heating in a Linear Discharge

Multichannel Neutral Atom Energy Spectrometers for Plasma Diagnostics