Study of electron waves in electrical discharge channels

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Abstract
The fast luminous pulses experimentally observed to propagate in electrical discharge channels, and believed to have a significant role in the process of electrical breakdown, are investigated, using a plasma fluid approach. These pulses fall in two regimes characterized by different average velocities of 106 and 108 m/s. We concentrate on the lower velocity pulses. A nondimensional analysis is used to show that these waves can be considered as longitudinal electron fluid waves driven by electron pressure gradients in weakly ionized plasmas. Model equations are derived considering each additional term in the momentum equation as a small but finite perturbation. In all cases, standard nonlinear fluid model equations are obtained as possible solutions. Electric forces lead to the Korteweg-deVries equation, viscosity to Burgers equation, and electron-neutral collisions to a damped wave equation. The propagation and attenuation of fluid waves along preionized channels is naturally associated with the formation of steps. It is suggested that thermalization must be associated with the injection of electrons from a source external to those in the preionized channel.

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