Electrical characteristics of a linear, nonequilibrium, MHD generator

Abstract

The purpose of this experimental study was to determine the electrical performance of a linear, segmented electrode, MHD generator. Various noble gases were shock-heated to plasma conditions that allowed MHD generator operation with Hall parameters ω e τ e ranging from 1 to 20 and ratios of electron to static gas temperatures of 1 to 2.5. For T e /T g > 1, the discharge structure in the generator was nonuniform. The major results were as follows. 1) By comparing the experiments with an MHD generator theory that included the effect of nonuniform extrathermal ionization, it was found that the Faraday generator operated in the normal mode, in which the current vector is approximately perpendicular to the axial flow direction, at all values of ω e τ e . The electrical performance of the generator at high ω e τ e was much better than that predicted for the shorted mode of operation in which the current vector is inclined in the axial Hall direction. 2) It was found that it was possible to obtain good agreement between the experiments and a simple uniform plasma, segmented electrode theory that included the Lorentz force effects, the electrode voltage losses, and the increased dissipation due to the plasma nonuniformities in the analyses. 3) Because of the relatively coarse electrode segmentation, it could not be established conclusively whether the effect of the electrothermal instabilities or the effect of finite electrode segmentation limited the maximum attainable Hall field.