Analysis of single array experiments on sphinx machine in 6 MA-800 ns regime for radiation effects and hedp studies

Abstract

Summary form only given. The Sphinx machine (F. Lassalle et al., 2008) is a 6 MA, 1 ?s driver based on the LTD technology, used for Z-pinch experiments. Despite the long implosion time (600 to 900 ns), Sphinx wire arrays with large radius (>40 mm) have already shown to behave and to be controlled by the same physical processes as faster Z-pinches. The use of a multi-microsecond current prepulse (H. Calamy et al., 2008) in addition to the classical nested wire array configurations have led to strong improvements of radiation output. Total power per unit length is multiplied by ~6 and FWHM is divided by ~2.5. This prepulse dramatically changes the ablation phase leading to a better axial homogeneity of both the implosion and the final radiating column. Nested arrays were previously used to mitigate the RT instabilities during the implosion phase but recent experiments with single arrays have shown that the benefit of the long prepulse technique is enough to allow stable implosions. As a result, using single array can lead to more efficient loads in terms of K-shell output since the implosion remains stable and, at the same time, the ?-parameter can be increased by reducing the mass of the load. Experimental results of single wire array loads of typical dimensions 50 mm in height with implosion time between 700 and 900 ns and radius varying between 40 and 80 mm are given. Parameters of the loads were varied in terms of radius and number of wires as well as material of wires. Comparisons with nested wire array loads are done and trends are proposed. Characteristics of both the implosion and the final radiating column are shown. MHD numerical simulations of single array become easier since there is no more interaction between the outer flow with the inner array and the complexity of the load description is reduced. This allows a systematic study using a mass injection scheme to benchmark simulations with experiments, providing basic physics understanding of such loads.