Development of hollow-cathode radiation sources. Part 2. Study of the effect of a cylinder placed in the cathode cavity on the emitted light intensity

Abstract

The effect of placing cylinders of different lengths and diameter in the cavity of hollow-cathode radiation sources on the light intensity emitted by the cathode material and the cylinder is examined. It was found that a cylinder of optimum length (e.g., 12–13 mm length in a cavity of 25 mm length and 5 mm i.d.) can take over the sample-holding role of the wall of the hollow cathode, i.e., it is the material of the cylinder and not the wall of the hollow that is predominantly evaporated and excited. When the surface area of the cylinder is increased and the correct voltage and current is chosen, only the tip of the cylinder or the sample placed there is excited. In this way the introduction of the sample is simple and reproducible. The effect of placing cylinders in the cavity on the electric field (the potential curves and lines of force) formed in the cathode and the excitation temperature of the metal vapour along the axis was determined. The potential curves penetrate only to the free tip of the cylinder placed in the cavity and the lines of force are also concentrated there. The maximum excitation temperature of the metal vapour (and the temperature maximum gradient) as well as the maximum line intensities emitted by the cylinder material are obtained when the length of the cylinder is about half the length of the cavity.