Characteristics of the Plasma Resonance Probe

Abstract

The plasma resonance probe was first studied by Takayama and his co‐workers in 1960. Since that time several attempts have been made to determine precisely the experimental and theoretical behavior of the resonance. This paper reviews the various contributions made so far, and develops further the explanation advanced in 1963 by Harp. Detailed experiments have been carried out to confirm the predictions: (i) that the resonance frequency lies below the local electron plasma frequency, (ii) that it is dependent on probe potential and probe size and, (iii) that the resonance should be highly damped when probe dimensions are smaller than a few electronic Debye lengths. If the resonance probe is to be of great practical importance, a simplified theoretical model describing its behavior is desirable. The theory of such a model is presented and compared to experimental results. The paper concludes with a discussion of improved methods of applying the resonance probe, and suggests a ringing technique which provides electron density measurements in laboratory discharges in times of the order of a few cycles at the electron plasma frequency.