Characterization of magnetohydrodynamic effects in a plasma opening switch

Abstract

Plasma dynamics are characterized in a long-conduction time plasma opening switch [Phys. Fluids B 4, 2368 (1992)] operated with densities and currents near the theoretical intersection of the magnetohydrodynamic (MHD) [IEEE Trans. Plasma Sci. PS-19, 400 (1991)] and electronmagnetohydrodynamic (EMH) [Phys. Fluids B 3, 1908 (1991)] regimes. In agreement with MHD theory, a hydrodynamic snowplow is observed to translate axially and reach the load end of the switch at opening. The axial motion of the front agrees with one-dimensional analytic predictions if the carbon plasma possesses an average ionization of 1, but is significantly less than theory if higher ionization levels are present. The axial motion of the plasma center-of-mass is significantly less than that expected from theory for any ionization level. The reduced center-of-mass motion is attributed to an ion loss mechanism in the unconfined switch plasma, an effect also observed in the total particle inventory, which saturates while the source plasma flux remains relatively constant. An ion lifetime of 450±15 ns (290±23 ns) for Z=1 (Z=2) results in a predicted center-of-mass motion in agreement with the measurements. Only minimal EMH effects are observed indicating, in contrast to theoretical predictions, that the switch is MHD dominated in this regime.