High density plasma opening switch experiments on Hawk

Previously, plasma opening switch (POS) experiments on the Hawk pulsed power generator have shown fast opening (<100 ns) into electron-beam diode loads, generating 1-2 MV after 0.5-1 /spl mu/s conduction time. The plasma density measured in these experiments was in the 10/sup 15/-10/sup 16/ cm/sup 3/ range. Plasma thinning by J/spl times/B forces during conduction reduces this density, ultimately leading to gap formation in the low density region. The Hawk experiments described here were designed to investigate this switching phenomenon with higher initial densities, in the 10/sup 17/ cm/sup -3/ range, to determine whether fast switching and high voltage could be sustained. This scaling is important for POS applications on future, higher energy generators. Experiments were performed with a relatively small center conductor radius (1.27 cm) and small plasma length (3 cm or 8 cm). Either 36 or 12 cable gun plasma sources were used to inject plasma into the coaxial switch region. The anode structure was varied to investigate techniques to increase the voltage when the switch opens. High voltage (1.5 MV) switching was observed at /spl sim/0.9 /spl mu/s conduction time when the radial gap between the inner and outer conductors in the switch region was reduced from 7 cm to 2 cm. These experiments demonstrate that, at least for some geometrical configurations, POS operation at 10/sup 17/ cm/sup -3/ density is similar to operation at one or two orders-of-magnitude lower density. Presumably, the plasma thinning mechanism results in a similar gap in all cases.