Transport of time-varying plasma currents by whistler wave packets

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Abstract
In a large laboratory plasma the properties of time-varying current systems have been studied experimentally. The parameter regime of interest involves magnetized electrons and unmagnetized ions. In the laboratory complete measurements of three-dimensional, time-varying vector fields of the total current density are obtained from magnetic probe measurements. Pulsed currents are observed to propagate at the speed of whistler wave packets. Their field structure forms flux-rope-like configurations which are electromagnetically force-free. Moving sources induce eddy currents which excite waves and form Cerenkov-like whistler wings. The radiation patterns of moving magnetic antennas and electrodynamic tethers have been investigated. The current closure between tethered electrodes across B/sub 0/ has been mapped. Nonlinear effects of large-amplitude, antenna-launched whistler pulses have been observed. These involve a new modulational instability in which a channel of high conductivity is formed which permits the wave/currents to penetrate deeply into a collisional plasma.