Sheath structure near a probe in a flowing plasma

Summary form only given, as follows. In most space applications, the electrostatic probes move with the spacecraft relative to the ambient plasma. In low Earth orbit, the relative velocity (~8 km/s) is highly supersonic with respect to the ion-acoustic speed (⩽1 km). The effects of such a relative motion on the sheath structures of a cylindrical probe in both magnetized and unmagnetized plasmas were studied by means of numerical simulations. For positive probe potentials, the sheath structure shows double-layer-type potential distributions. The current collections by the probe for the cases with and without the magnetic field were compared, showing a significant enhancement of currents due to the cross-field transport of electrons. This transport is facilitated by the E×B drifts in a highly asymmetric potential structure around the probe for nonzero magnetic fields. For the case with the magnetic field, the time-averaged current was found to vary approximately linearly with the flow velocity V₀. For the typical value of V₀ (~8 km/s) in low Earth orbit, the enhancement of the current through cross-field plasma transport was found to be an appreciable fraction of the current predicted by previous models, which do not account for cross-field plasma transport