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Magnetohydrodynamic experiments in an electromagnetic shock tube Driver, Harry Stephen Thackwray

Abstract

The flow conditions in a low attenuation electromagnetic shock tube are discussed and compared with those in pressure driven shock tubes and conventional electromagnetic shock tubes. The low attenuation electromagnetic shock tube differs from the conventional electromagnetic shock tube in that it incorporates a diaphragm separating the high pressure driver section from the low pressure expansion section. It was shown that the shock tube gives a plane shock front and a region of shock heated gas separated from the driver gas by a non-plane contact surface. The electrical conductivity of shock heated argon was measured for shock speeds of from Mach 8 to Mach 35, and downstream pressures of from 0.01 to 2.0 mm Hg, and was found to agree with theory at the higher downstream pressures but to fall below the theoretical values at the low pressures. The low values of conductivity were attributed to a non-attainment of equilibrium behind the shock front due to the greater relative importance of electron diffusion at low densities. The shock heated gas was used as the working fluid in two magnetohydrodynamic power generators. In the first the internal resistance of the generator was measured as a function of electrode area and generator current. It was concluded that at high currents a cathode spot was formed, and the measured resistances were related to a theory of cathode spot conduction. In the second generator some effects of the non-scalar conductivity of the plasma at high magnetic fields were investigated. It was shown that the values of Hall voltages in a magnetohydrodynamic generator agree with theory, and can be used to obtain an estimate of the electron density in the plasma. The reduction of the generator current by Hall currents was measured.

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