Properties of a high-current discharge in alkali-metal-seeded rare gases.
Ellington, Henry I.
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ELLINGTON, H.I. 1969. Properties of a high-current discharge in alkali-metal-seeded rare gases. Robert Gordon's Institute of Technology, PhD thesis.
This thesis is an account of a detailed investigation of the properties of a recently-discovered gas discharge - a discharge that operates at a few volts or tens of volts, and which carries a current of the order of amps through a mixture consisting of a hot, atmospheric-pressure rare gas (the "diluent") to which a small amount of alkali metal vapour has been added as an easily-ionised "seed". It is shown that the establishment of the discharge under study is brought about by the breakdown of the gas, which occurs at a breakdown voltage that depends mainly on the electrode spacing, seed pressure, and choice of diluent gas. The discharge itself is shown to consist of two main regions, namely, a constricted, cylindrical positive column that extends from the anode to within a short distance of the cathode, and a thin, glowing sheath that covers the entire cathode surface; the two regions are separated by a dark space. The positive column is shown to expand as current increases, while the value of its electric field is shown to depend mainly on the discharge current, seed pressure, and choice of diluent gas, and hardly at all on the gas temperature or choice of seed metal. The cathode fall is shown to depend mainly on the discharge current, seed pressure, and choice of seed metal. The breakdown of the gas, the positive column of the discharge, and the cathode regions of the discharge are discussed in successive chapters.