Reproducible control of the voltage of Langmuir probes in steady-state and afterflow plasma (regulation circuit)

A regulation circuit is described that makes possible very accurate probe measurements by virtually eliminating work function drift and plasma potential fluctuation effects on the probe characteristic. By the use of a reference probe and repeated measurement of the floating potential of the active probe in time intervals that are short compared to the time constant of the work function drift, a voltage scale can be established for the probe with an accuracy and repeatability of a few mV. As an application of the method, the rapid thermalization of the electrons and the appearance of the fundamental diffusion mode in a hydrogen afterglow are shown.