The origin of the plasma in an electromagnetic shock tube

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Abstract
A pair of electrodes was placed in an electromagnetic shock tube to measure the electric field induced by the flow of an argon plasma through a transverse magnetic field. This investigation suggested that the plasma consisted of two regions, the first of which was non-luminous. Flow velocities, deduced from the variation of induced voltage with electrode separation, were compared with luminous front velocities measured photoelectrically. The first plasma region moved more slowly than the second, and its velocity and duration were consistent with shock-heating. The second region, which was dominant in most, experiments, flowed at the luminous front velocity, and had probably been ejected from the driver discharge. It is proposed that the flow velocity in the second region exceeded that in the first owing to an extensive leakage of gas through the boundary layer at the contact surface.