Theory of Langmuir Probe Used in a Re-entry Vehicle Surrounded by a Flowing Continuum Plasma

Abstract

The present piece of work reviews the theory of Langmuir probes in free-molecular stream with a classical approach and attention is accorded to the interpretation of data for the probes in saturation region, and to plasmas in which the characteristic ion and electron energies are comparable. Various methods for interpreting the probe measurements are enumerated. This information is employed in the subsequent theory for cylindrical and spherical probe in a flowing continuum plasma for an electron current collection, which concerns the performance of Langmuir probes flown abroad re-entry vehicles. The sheath region is considered as collisionless and rest of the plasma as collision dominated. The one-dimensional fluid equations are solved with the proper Poisson's equation. The theory deals with the probe at arbitrary potential and under the conditions that the drift velocity is greater than the electron thermal velocity and probe radius to mean free-path ratio, greater than unity. The theoretical results are in agreement with some known experimental results.