Experimental Methods and Conditions

Abstract

The probe method, suggested by Langmuir in 1923, is still one of the most widely used methods in the determination of plasma parameters. There are several reviews and monographs [38-40] where the fundamentals of the probe method are given and references to earlier work are cited. In this method an electric probe, i.e., a small electrode of spherical, cylindrical, or planar shape, is introduced into a discharge and subjected to a potential lower or higher than the plasma potential V₀ in the region under investigation. If the probe is kept at a potential different from V₀, it produces in the surrounding space an electric field which accelerates charges of one sign and repels charges of the opposite sign. In general, the total current i reaching a probe has the ion i_i and electron i_e components.