High current spark channels

Measurements have been made on high current (up to 265 kA) spark channels in air, argon and hydrogen. The voltage gradients existing in the channels were determined by oscillographic measurements and were found to increase with increasing current in the range studied. Power inputs of tens of megawatts per centimetre length of channel were derived from the measured voltage gradients. Rotating-mirror photographs of the discharges were taken, using a camera with a resolution better than 1/5 μs. The photographs obtained show a number of interesting features which are peculiar to these high current discharges, the chief one being the bright central core of the discharge, which was photographed in every case. Temperatures of about 10 5 · K were estimated from electron mobility considerations. The central core of the discharge appears to be due to the self-magnetic "pinch" effect, and calculations based on this inference suggest that high ion densities (similar 10 19 per cm 3 ) exist in the centre of the core; the energy requirements for such conditions are compatible with the measured power inputs.