Modelling of sheaths, presheaths, current-voltage characteristics and double probes in low-pressure plasmas in coaxial and concentric geometries

Abstract

The theory of positive column is generalized including additional non-emitting electrodes within the plasma and at the wall. Taking into consideration cylindrical and spherical geometries yields a theory of current carrying sheaths and presheaths and a theory of asymmetric double probes. Single probe operation in bounded plasmas can be approximated. A steady state compressible two-fluid model is used throughout the plasma. Various conditions for probe operations can be described as collision dominated and collisionless plasmas, the thick and the thin sheath regime and the transition regions. The radii of the regions of electron collection and of ion collection for the inner and outer walls are calculated. Detailed results are given for number densities, drift velocities, the electrical potential and the current-voltage characteristics. The floating potentials depend on the curvature of the electrode as shown analytically and numerically.