Plasma evolution of a POS: comparison of theory and experiment on ACE 4 and HAWK

The evolution of the plasma in a high density, long conduction time POS can have a substantial effect on the performance of the switch. The motion of the plasma and its dependence on the geometry of the initial injection region and of the downstream vacuum feed influences not only the opening characteristics of the POS but also the timing of its interaction with the load. Two dimensional MHD-Hall calculations have been performed to determine the evolution of the POS plasma in the coaxial geometry of ACE 4 and of HAWK. The computations utilize initial conditions provided by interferometric diagnostics. Results of the calculations show the plasma densities, velocities, positions and other plasma parameters through and beyond the conduction phase following excitation by megampere level currents. The results for density are compared with measurements taken using axial and chordal interferometry; the latter probing regions that are downstream of the POS.