Implosion dynamics of long-pulse wire array Z pinches

Recent improvements in Z-pinch wire array load design at Sandia National La boratories have led to a substantial increase in pinch performance as measu red 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 mas s arrays and comparable or higher velocity implosions to be reached, possib ly extending these results. As the current is pushed above 20 MA, a convent ional machine design based on a 100 ns implosion time results in higher vol tages, hence higher cost and power flow risk. Another approach, which shift s 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 ex perimental 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)] machin es. In this paper, both experimental and two-dimensional computational mode ling of the first long implosion time Z experiments will be presented. The experimental data shows broader pulses, lower powers, and larger pinch diam eters compared to the corresponding short pulse data. By employing a nested array configuration, the pinch diameter was reduced by 50% with a correspo nding increase in power of > 30%. Numerical simulations suggest that load v elocity is the dominating mechanism behind these results. (C) 2000 American Institute of Physics. [S1070-664X(00)96005-1].