POS experiments in the MHD and EMH regimes

Summary form only given, as follows. Plasma dynamics are characterized in a long-conduction-time planar plasma opening switch (POS) using measurements of the magnetic field and electron density. In the first set of experiments, the POS is operated near the theoretical intersection of the predicted MHD and EMH regimes. In qualitative agreement with MHD theory, a hydrodynamic snowplow is observed to translate axially down the switch and reach the load end at the start of the opening phase. Theory modifications to include ion losses bring the plasma dynamics into quantitative agreement with MHD theory. In the second set of experiments, the POS is operated in a regime where EMH effects are expected to control the switch conduction. For the measured electron density minimum in the radial center of the switch, magnetic field convection into the plasma is predicted near the anode with expulsion near the cathode. In conflict with the model, measurements show extensive field penetration across the switch, with broad, predominantly radial, current channels. To further isolate possible EMH effects, the switch polarity was reversed. Measurements again show broad, predominantly radial, current channels similar to those measured with the original polarity. The measurements indicate that while some effects are present that may be attributable to EMH, the conduction phase of the POS operated in this regime is controlled by other processes.