Pulsed currents carried by whistlers. IX. {bold {ital In situ}} measurements of currents disrupted by plasma erosion
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States)
In a magnetized laboratory plasma described in the companion paper [Stenzel and Urrutia, Phys. Plasmas {bold 4}, 26 (1997)], a large positive voltage step (V{gt}kT{sub e}/e) is applied to electrodes. The current front propagates in the whistler mode in the parameter regime of electron magnetohydrodynamics. The topology of the current density is that of nested helices. Large transient currents in excess of the electron saturation current can be drawn. A transient radial electric field associated with the current rise, excites a compressional, large amplitude, radially outgoing sound wave, which leaves the current channel depleted of plasma. The current collapses due to the density erosion. Electric field reversal excites a rarefaction wave which leads to a partial density and current recovery. Periodic plasma inflow and outflow cause the current to undergo strong relaxation oscillations at a frequency determined by the electrode diameter and the sound speed. In addition, a broad spectrum of microinstabilities is observed in regions of high current density. For drift velocities approaching the thermal speed, the spectrum extends beyond the ion plasma frequency ({omega}{sub pi}) up to the electron plasma frequency ({omega}{sub pe}). Correlation measurements above {omega}{sub pi} reveal modes propagating along the electron drift at speeds above the sound speed but well below the electron drift speed. {copyright} {ital 1997 American Institute of Physics.}
- OSTI ID:
- 434296
- Journal Information:
- Physics of Plasmas, Vol. 4, Issue 1; Other Information: PBD: Jan 1997
- Country of Publication:
- United States
- Language:
- English
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