Stagnation Point Langmuir Probe in a Shock Tube-Theory and Measurements

Abstract

Langmuir‐type probes consisting of a flat‐headed circular cylinder with a collecting electrode at the stagnation point are placed in a shock tube and exposed to supersonic ionized air flow at ion mass fractions less than 10⁻⁴ and initial shock tube pressure of 1 cm Hg. Stagnation point measurements of ion current density are obtained using negative electrode potentials. The exact gasdynamic stagnation point boundary layer equations and the one‐dimensional Poisson equation are solved for an axially symmetric blunt body and ion mass fractions less than 10⁻². Calculations of the ion‐electron flow in the stagnation point boundary layer are presented for negative electrode potentials. The measurements and calculations agree within the experimental accuracy and the precision to which the physical constants are known.