Abstract
The paper analyzes two concepts of conduction in a low-density plasma opening switch: based on the formation of a bipolar space charge layer subject to unlimited cathode emissivity (bipolar model) and of a unipolar ion layer due to electron motion off the cathode under an electric field induced by magnetic field penetration into the plasma (unipolar model). A comparison of unipolar-model expressions with widely known experimental data shows that the conduction current behaves strictly as Ic µ n1/2 at any plasma bridge length in the range of plasma densities from ~1011 cm-3 to ~1014 cm-3 and current rise rates from ~0.3 kA/ns to ~4 kA/ns. Holding the conduction current constant at any bridge length l requires that nl2 be constant. As the magnetic field rise rate is varied, the conduction current follows Ic µ Ḃ1/2. These results differ radically from what is predicted by the bipolar model. Also presented in the paper are arguments of why the axial current channel width varies nonmonotonically during a pulse and estimates of the electron temperature at different plasma densities and field rise rates.