Langmuir probe response to periodic waveforms

The behavior of a Langmuir probe modulated by an externally applied signal differs from its static behavior owing to the presence of additional steady and alternating components of probe current. These may be interpreted to yield data on such plasma parameters as electron temperature and density and electron velocity distribution. Considerable progress has been made recently in this branch of plasma diagnostics. This work is surveyed here and is extended by an analysis of a new ac method of determining electron density and temperature. The new method depends on the measurement of probe admittance and should have useful applications to ionospheric probing by rockets and satellites. Details of an illustrative example are given. Some of the implications of the theory presented bear on the accuracy of probe measurements of electron velocity distributions made by second derivative methods. These errors are discussed briefly.