Plasma injection technique for species separation and magnetic field penetration experiments

Summary form only given. We are studying species separation and magnetic field penetration in current-carrying plasmas in a coaxial plasma opening switch geometry¹. PIC modeling has shown that these processes are dependent upon the radial density gradient and multi-species composition of the plasma². Historically, flashboards, cable guns³, or an inverse pinch source⁴ have been used to inject plasma into the switch region before the main power pulse is applied. In this case, the plasma is injected using Marshall guns⁵, allowing greater control of the initial density gradient and composition than with other injection methods. A ribbon beam interferometer, in a Mach-Zehnder configuration, passes axially through the 4-cm-long, 2-cm-wide switch region to measure the radial dependence of the line-integrated electron density as a function of time. Measurements are taken both for the guns alone and during short circuit plasma opening switch shots on NRL´s Hawk pulsed-power generator (640 kV, 700 kA, 1.2 μs rise time) to determine the initial density gradient and its evolution as the plasma interacts with the driving magnetic field. Experimental data are compared with previous opening switch experiments using Marshall guns and current particle-in-cell simulations.