Implosion dynamics of long-pulse wire array Z pinches

Recent improvements in Z-pinch wire array load design at Sandia National Laboratories have led to a substantial increase in pinch performance as measured by radiated powers of up to 280 TW in 4 ns and 1.8 MJ of total radiated energy. Next generation, higher-current machines will allow for larger mass arrays and comparable or higher velocity implosions to be reached, possibly extending these results. As the current is pushed above 20 MA, a conventional machine design based on a 100 ns implosion time results in higher voltages, hence higher cost and power flow risk. Another approach, which shifts the risk to the load configuration, is to increase the implosion time to minimize the voltage. This approach is being investigated in a series of experimental campaigns on the Saturn [C. Deeney et al., Phys. Plasmas 6, 3576 (1999)] and Z [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] machines. In this paper, both experimental and two-dimensional computational modeling of the first long implosion time Z experiments will be presented. The experimental data shows broader pulses, lower powers, and larger pinch diameters compared to the corresponding short pulse data. By employing a nested array configuration, the pinch diameter was reduced by 50% with a corresponding increase in power of >30%. Numerical simulations suggest that load velocity is the dominating mechanism behind these results.