Hybrid drift instabilities and energy coupling in long-risetime Saturn, aluminum, implosions

Summary form only given, as follows. Two recent series of Al:Mg wire array Z-pinch experiments were conducted on the Saturn pulse-power generator, which was operated in a long pulse-risetime mode. In these experiments, in which current risetimes were in excess of 150 ns, absorbed energy enhancements were observed that varied between factors of 2 to 4 times the energy input expected from j/spl times/B work alone. In the past, it was conjectured that some form of anomalous resistivity was needed to account for the extra energy input, while recently, a new idea was proposed based on the buildup of internally generated flux-tubes of magnetic field energy. In fluid dynamic modeling of Z-pinch implosions, energy from the generator flows into the pinch through the pinch surface where, it has been argued, a lower-hybrid-drift instability is generated that can significantly increase the electrical resistivity. Temperature increases at the pinch surface, which are driven by Ohmic heating, lead to density decreases. Since these temperature increases reduce Spitzer resistivity while density decreases lead to drift-wave resistivity increases, this latter resistivity can be made to greatly exceed the Spitzer resistivity. We will show how this development has the potential to produce large increases in the energy coupled to the Z-pinch load. Tradeoffs in this coupling mechanism occur since increases in plasma resistivity speed the diffusion of the current into the plasma, thereby lowering the Ohmic heating at the surface. These tradeoffs will be discussed and illustrated. It will be shown that large variations in the calculated energy coupling are potentially possible and that these variations can mirror the pinch behavior seen in the Saturn experiments.