The transport of timehyphen;dependent current between electrodes in contact with a large laboratory magnetoplasma is examined experimentally. Single electrodes biased with respect to the chamber wall or pairs of electrically floating electrodes are used to produce pulsed currents (ohgr;ciLt;2pgr;/Dgr;tLt;ohgr;ce). The associated magnetic field vector,B(r,t), is measured in space and time, and the total current density is calculated fromJ(r,t)=nabla;times;B(r,t)/mgr;0. The current front is found to propagate at a characteristic wave speed, which does not depend on current amplitude or polarity. The transient current spreads acrossB0within a conical region, which depends on source geometry and plasma parameters. It is shown by Fourier transformingB(r,t) intoB(k,ohgr;) that the transient fields consist of a spectrum of oblique lowhyphen;frequency whistler waves. In Fourier space, the inductive and space charge electric fields are calculated from Faradayrsquo;s law and the assumption thatEtot=Eind+EscalongB0is negligible. Inverse transforming yieldsE(r,t). The transient wave fields (B,J,E) exhibit multiple induction effects and the formation of space charges. The results are relevant to pulsed Langmuir probes, beams, and antennas as well as moving steadyhyphen;state magnetic/current sources such as particle collectors on spacecraft and magnetized asteroids (e.g., Gaspra).
展开▼
