Theory of Ion Boundary Layers

Abstract

Theories are presented for the electric boundary layers that form on flat-plate and cylindrical probes aligned parallel with a high speed flow, when the probe potential is large and negative. Both slightly ionized continuum flows and collisionless plasmas are considered. In the former case, the probe potential is supposed sufficiently large to make the electric boundary layer thick compared with the viscous boundary layer. The corrections arising from the presence of the viscous boundary layer are calculated. The cases considered are solved either by an integral method, or by a quasi-one-dimensional method. The results obtained can be used to determine the freestream ion density from the current measured experimentally. A comparison is made between theory and some available experimental data.