Behavior of electron-emitting plasma probes in the space-charge-limited regime

Abstract

The properties of cylindrical electron‐emitting plasma probes are reviewed. Poisson's equation is formulated and solved for a cylindrical emissive probe biased several volts negative of plasma potential and operating in the space‐charge‐limited regime. It is shown that in this regime the emitted current at fixed voltage is proportional to the reciprocal of the Debye length. The theory is shown to be in good agreement with experimental results. Expected deviations of probe behavior from the theory and the theory's limitations are discussed. Due to the emission limitations of such probes the technique appears useful only for those plasmas whose Debye length is greater than about 10⁻² cm.