Electrical discharges

Abstract

Recent developments in electrical discharges are surveyed under the main headings: The Breakdown of Gases in Static Fields; High-Frequency Discharges; Cold Emission Phenomena; and The Regime of Space Charges. Investigations of the fundamental process of electrical breakdown at high and low pressures for long and short gaps by measurements of the growth of ionization current just prior to breakdown are described; a generalized view is made possible regarding breakdown as a consequence of the development of pre-breakdown ionization currents by primary and secondary processes which are themselves controlled by the nature and geometry of the cathode. Properties of E and H high-frequency discharges are outlined, and a general theory of high-frequency breakdown and of maintained discharges is given. It is shown how further knowledge of the behaviour of ionized gases is obtained which has led to a greater under-standing of collisional processes such as attachment and recombination. Various applications are indicated. Studies of the important role played by surface films in the cold extraction of electrons from electrodes are described, and applications of the results to arc discharges, high-voltage high-pressure breakdown, and cathode phenomena in breakdown are indicated. Work on the nature of radio-frequency plasma oscillations, and of the generation of noise by discharges, is described. An account of recent work on arc discharges is given, dealing particularly with cathode phenomena and the thermal and optical properties of the arc column.