Pulsed currents carried by whistlers. VI. Nonlinear effects
- Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States)
In a large magnetized laboratory plasma ({ital n}{approx_equal}10{sup 11} cm{sup {minus}3}, {ital kT}{sub {ital e}}{ge}1 eV, {ital B}{sub 0}{ge}10 G, 1 m {times} 2.5 m), current pulses in excess of the Langmuir limit (150 A, 0.2 {mu}s) are drawn to electrodes in a parameter regime characterized by electron magnetohydrodynamics ({omega}{sub {ital ci}}{lt}{omega}{lt}{omega}{sub {ital ce}}). The transient plasma current is transported by low-frequency whistlers forming wave packets with topologies of three-dimensional vortices. The generalized vorticity, {bold {Omega}}, is shown to be frozen into the electron fluid drifting with velocity {ital v}, satisfying {partial_derivative}{bold {Omega}}/{partial_derivative}{ital t}{approx_equal}{nabla}{times}({ital v}{times}{bold {Omega}}). The nonlinearity in {ital v}{times}{bold {Omega}} is negligible since {ital v} and {bold {Omega}}({ital r},{ital t}) are found to be nearly parallel. However, large currents associated with {ital v}{ge}(2{ital kT}{sub {ital e}}/{ital m}{sub {ital e}}){sup 1/2} lead to strong electron heating which modifies the damping of whistlers in collisional plasmas. Heating in a flux tube provides a filament of high Spitzer conductivity, which permits a nearly collisionless propagation of whistler pulses. This filamentation effect is {ital not} associated with density modifications as in modulational instabilities, but arises from conductivity modifications. The companion paper [Stenzel and Urrutia, Phys. Plasmas {bold 3}, 2599 (1996)] shows that, after the decay of the transient wave magnetic field, magnetic helicity remains in the plasma due to temperature-gradient driven currents. {copyright} {ital 1996 American Institute of Physics.}
- OSTI ID:
- 285578
- Journal Information:
- Physics of Plasmas, Vol. 3, Issue 7; Other Information: PBD: Jul 1996
- Country of Publication:
- United States
- Language:
- English
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