Formation and Role of a Hollow-Cathode Plasma Plug in Mass-Spectrometric Analysis

Abstract

The use of plasma electron and ion sources based on a glow discharge is often restricted by a too high plasma-forming gas pressure in the process volume. Experiments with a new design of a hollow cathode, a type of glow discharge, are described in this paper. It was found that, if a cap with an orifice is arranged at the vertex of a cylindrical hollow cathode (the orifice diameter is 10 to 90% of the inner diameter of the hollow cathode), a plasma plug, which offers resistance to a plasma-forming gas flow from the cathode hole to the vacuum chamber, is formed in the cathode hole near the orifice. As a result, a pressure drop is formed between the cathode hole and the vacuum chamber. This pressure drop depends on the orifice diameter, and it can be as high as three orders of magnitude with the use of a hollow cathode with an internal diameter of 20 mm and an orifice diameter of 4 mm in the cap at the cathode vertex.