Modified Snowplow Model for Coaxial Plasma Accelerators

Abstract

In order to explain previously observed deviations of measured plasma velocities from velocities predicted by computer solutions based on a snowplow model, the experimental and computer data are here extended over a much wider range of electrode configurations, capacitor potentials, and gas densities in the shock tube. At low densities the experimental velocity curves fall below the predicted curves because of material evaporated from insulation and electrodes. At high gas densities the experimental velocity curve for the largest center electrode coincides with the predicted curve, but for center electrodes of successively smaller diameter the measured curves lie progressively farther above, but parallel to, those predicted, up to a factor of 5.5 times for the smallest electrode used. These results are explainable in terms of a modified snowplow model postulating an effective annular region adjacent to the center electrode, whose thickness is of the same order as the electrode radius, such that the force due to the magnetic pressure inside this annulus acts on only the gas contained within it to produce the measured velocity.