Free-molecule Langmuir probe and its use in flow-field studies.

Abstract

Experiments were performed in a steady, low-density flow of argon plasma to determine the behavior of small cylindrical Langmuir probes in high-speed flows. In particular, the dependence of the ion current on the probe radius and on flow speed was investigated and correlated with the ratio of probe radius to Debye length and the ratio of flow speed to the ion acoustic speed. The probes were then employed to study the electron temperature and number density distributions in the stagnation region of a flat-nosed cylinder in supersonic flow. The Reynolds number Re^ based on model diameter and viscosity at stagnation temperature, was in the range 70 to 125, whereas the Langmuir probes were free molecular. The charged-particle number density distribution measurements provided a graphic demonstration of the merging of the bow shock and the boundary layer at Re^ ^ 100, and also furnished some evidence of the diffusive separation of the ions and atoms in the shock wave. Nozzle and free-jet flowfields were probed also. Nomenclature