An analysis of the anomalous high-current cathode emission in pseudospark and back-of-the-cathode lighted thyratron switches

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Abstract
An analysis of the anomalously large cathode emission recently observed in the superdense glow of pseudospark and back-lighted thyratrons is presented. These switches are low-pressure (27 Pa H2) glow-discharge pulsed-power devices. After operating at peak discharge currents of 6–8 kA and pulse durations of 0.5–1 μs, the surface surrounding the cathode hole was found to have been homogeneously melted within a radius of ≊4 mm indicating that the discharge is a superdense glow discharge, not an arc, with a cross-sectional area on the order of 1 cm2. This conclusion is also supported by streak camera measurements. The current density at the cathode surface under these conditions is 5–10 kA/cm2, several orders of magnitude larger than that of thermionic cathodes in common thyratrons. This high-current density is explained by intense cathode heating from a high-current density ion ‘‘beam’’ produced in the cathode fall during the initial stage of current buildup. The surface heating resulting from this ‘‘beam’’ yields a significant field-enhanced thermionic emission of electrons.

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