New Applications of Langmuir Probes

Abstract

In this work, two new possibilities for standard probe diagnostics are described. The first one can be used to study isotropic, collisionless low-pressure plasma in which the electron energy distribution function is close to a Maxwellian one. In such plasmas, the Boltzmann law, Bohm effect, and 3/2 power law are valid. Use of corresponding system of equations for cylindrical Langmuir probes allowed for measurements of probe sheath thicknesses and the mean ion mass. The solution of this task was provided by accurate probe diagnostics of inductive xenon plasma at pressure p = 2 mTorr that resulted in the determination of the Bohm coefficient C_BCyl = 1.22. The second possibility of probe diagnostics includes a method and device for evaluation of ion current density to a wall under a floating potential using a radially movable plane wall Langmuir probe simulator. This measurement in the same xenon plasma served as the basis for development of an ion source in which the given wall was represented by an ion extracting electrode of the ion extraction grid system.