Properties of electric discharges sustained by a uniform source of ionization

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Abstract
A theoretical examination is made of the class of discharges which are sustained by a uniform source of electron and ion pairs produced between plane‐parallel electrodes. The calculations account for drift, diffusion, and recombination of the charge carriers, ionization of the gas by electrons, and distortion of the applied field due to space charges. It is found that the number and current‐density profiles of electrons and positive ions in the gaseous discharge are of three different types, where (i) the electron density is several orders of magnitude lower than the positive‐ion density at all interelectrode positions, (ii) a plasma region exists, but the electric field in the plasma is negligible compared with that in both electrode sheaths, and (iii) significant ionization occurs in the cathode‐sheath region. Examples of such discharges for which numerical solutions are given are as follows: for type (i), a γ‐ray photoionization chamber with a current density j2; for type (ii), a fission fragment ionization chamber used as a neutron detector where j∼1 mA/cm2; for type (iii), a discharge similar to that of a gas laser sustained by ionization from an electron beam where j for the laser ∼1 A/cm2. Derived current‐voltage characteristics for discharges in argon corresponding to types (i) and (ii) are in reasonable agreement with experiment and also with characteristics derived analytically by considering the cathode‐sheath region only and neglecting diffusion and ionization by electrons.