Canal-ray positive-ion sources

The paper deals with the positive-ion output available from cold-cathode glow discharge tubes with a canal drilled through the cathode. The importance of obtaining large canal-ray currents for high-voltage positive-ion bombardment work is stressed, and a brief preliminary discussion of previous work given. The reasons for adopting canal-ray sources are then discussed. A study of the discharge mechanism of such sources reveals several interesting features. In the measurement of intense positive-ion currents, precautions were taken to avoid errors due to secondary emission of electrons from the collector, and, a satisfactory technique having been developed, exhaustive measurements were taken on canal-ray sources of two types differing in detail from each other. The necessity for using a low gas output is stressed, and the effect on yield of varying the canal-flow impedance is studied. Some interesting results were obtained by the use of a focussing diaphragm in the source, e.g. yields were considerably increased, but with a higher tube pressure. Total ion currents up to 2 ma. in strength were obtained. The presence in the canal-ray beam of large numbers of neutral particles was shown by an experiment on electrostatic deflection of the rays after leaving the canal. The final part of the paper deals with magnetic deflection of the beam and its analysis into different groups of ions. This work was done with a high-voltage cascade acceleration tube, and qualitative data on collision processes in molecular hydrogen are given.