POTENTIAL STRUCTURE NEAR A PROBE IN A FLOWING MAGNETOPLASMA AND CURRENT COLLECTION

The distributions of plasma and potential near an electric probe in a relative motion with respect to a magnetized plasma are studied by mea ns of three-dimensional (3-D) numerical simulations. The relative moti on is simulated by a plasma flowing past the probe across the ambient magnetic field. The plasma now is imposed by a convection electric fie ld (E) under bar(o). A probe with a positive potential bias is conside red. The prominent features of the potential distribution include (1) wings of positive potential perturbations extending along the magnetic field and swept forward in the direction of the plasma now and (2) a ''fan'' shaped structure in planes transverse to the magnetic field in the region where the convection electric field (E) under bar(o) is op posed by space charge electric fields. The wing-like structure can be interpreted in terms of electrostatic plasma waves belonging to the ob lique resonance cone in a magnetized plasma. The relative flow causes the formation of a ''bow shock'' in front of the probe, where plasma d ensity is enhanced due to the combined effect of the retardation of th e flowing ions and the modification in the (E) under bar x (B) under b ar drift of the electrons in the sheath of a positive probe. The elect ron collection by the probe is significantly enhanced above the theore tical upper bound current obtained from the conservation of energy and the canonical angular momentum for the case without the relative moti on The current in the plasma, contributing to the collection of electr ons by the probe, flows in a magnetic field-aligned channel in the vic inity of the probe where electric fields parallel to the magnetic fiel d are relativley strong. Electron flux is fed into the channel all alo ng its length by the (E) under bar x (B) under bar drift in the self-c onsistent electric field, considerably enhancing the current collected by the probe. The field-aligned current channel is localized near the probe where parallel electric fields dominate; it does not extend to infinity along the probe's magnetic shadow, unlike that for the case o f a nonflowing plasma.