Adiabatic efficiency of aa supersonic Faraday MHD (magnetohydrodynamic) generator and its relation to Joule dissipation in the MHD channel were studied in a shock tube experiment. The adiabatic efficiency of 39.7% was obtained at the enthalpy extraction of 8.3%. A dissipation process, which reduces the adiabatic efficiency, is examined by evaluating loading parameters and entropy productions caused by the Joule dissipation. At low load resistances, large Faraday currents in the channel upstream cause extremely large Joule dissipation in both the main flow and the region near the electrodes. It is confirmed experimentally that a high loading parameter yields a high adiabatic efficiency because Joule dissipation is small throughout the MHD channel.

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The production of non-equilibrium plasma and the fluid flow with the MHD interaction are examined experimentally with a shock-tube driven disk channel with no loading electrodes. For low magnetic flux density and low seed fraction, where non-uniform and unsteady plasma is generated, the static pressure decreases onotonically in the radial direction, although the pressure increases in the entire region of the channel in comparison with the value under no MHD interaction. For magnetic flux density and seed fraction above some critical values, a fairly uniform plasma is produced. The static pressure, however, is found to increase abruptly in the channel and the total pressure is considerably reduced at the location, where the abrupt pressure increase ocuurs. These facts imply that steady and uniform plasma should be produced without locally constricted strong Lorentz force to improve the adiabatic efficiency of a disk MHD generator.

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The effects of externally applied radio-frequency (rf) electromagnetic field on the non-equilibrium and the performance of a disk MHD generator were examined experimentally. As a preliminary experiment, the plasma production by applying the rf electromagnetic field was attempted in the disk generator (Disk-PIA), in which rf induction coils were embedded in one-side disk wall, under the conditions of no seeding, no flow and no magnetic filed. From the result of the preliminary experiment, it was confirmed that the argon plasma (_??_110Torr) was produced uniformly in the azimuthal direction by the rf electromagnetic field even in the presence of exposed anodes in the faced disk wall and metallic support at the disk center. In MHD power generation experiments with the Disk-PIA installed in the shock-tube facility, the increase in the electrical output and more indiscrete discharge attributed to the rf electromagnetic field were verified with well reproducibility for the first time.

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Magneto-acoustic Instability of nonequilibrium plasma in a disk MHD generator was investigated experimentally and analytically. At a low load resistance, a striated discharge structure was observed and it was found that the resonance line spectrum of cesium and recombination radiation fluctuated simultaneously under the conditions of some seed fractions. Furthermore, it was found that the fluctuation of recombination radiation became smaller when a high enthalpy extraction was obtained. On the other hand, at a high load resistance, a large fluctuation of static pressure with frequency of 2[kHz] which was thought of a magneto-acoustic wave was observed and it seemed that the pressure wave propagated upstream against the flow. Optical measurements suggested that the fluctuation of electron density did not depend on the fluctuation of electron temperature in the case of existence of the pressure wave. In addition, growth rates of magneto-acoustic wave were calculated by a liner perturbation theory, and the growth rate was found to get smaller with increase of seed fraction because the Hall parameter becomes lower at higher seed fraction. This analytical prediction agreed well with the experimental result. The analysis also indicated that the wave was amplified by a spatial gradient of the collision force between electrons and heavy particles which was caused by an increase in local collision frequency.

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In order to investigate effects of plasma behaviors on fluid-dynamical predictions of generator performance, local steady-state analytical calculations have been conducted. Effective Hall parameter and effective electrical conductivity have been estimated by taking a linear theory on the ionization instability into account. The numerical calculations have been compared with experimental results. Although a fully ionized seed (FIS) condition which suppresses the instability provides the highest generator performances, the FIS plasma could be realized only under the condition of high seed fraction in the experiments. The theoretical analysis implies that the instability due to the insufficient or the excessive electron temperature is a performance-limiting factor. It is possible to estimate effects of the plasma condition on the generator performance by the present simple analysis.

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