Flush probe studies of plasma flow over a flat plate: theory

Abstract

The transient electrical properties of a planar probe which is immersed in a flowing continuum plasma and in which the flow velocity is parallel to the probe surface are studied theoretically. When the probe is pulsed negatively, the resultant ion current overshoots its final equilibrium value. The time constant for recovery from this overshoot is shown to yield the information about the plasma flow over the probe. When the plasma sheath edge is inside the hydrodynamic boundary layer it is able to directly probe the velocity structure of the hydrodynamic boundary layer. The theory used to describe the probe's electrical properties differs from other thick sheath theories in that both gas compressibility and ion/electron recombination effects are considered.