Improved large diameter wire array implosions from increased wire array symmetry and on-axis mass participation

Abstract

Aluminum wire array, Z-pinch experiments have been performed on an 8 MA generator using arrays consisting of 24, 30, and 42 wires. These experiments were designed to scan through a region of ͑array mass, implosion velocity͒ space in which greater than 30% conversion of the implosion kinetic energy into K-shell x rays was predicted to occur ͓Thornhill et al., Phys. Plasmas 1, 321 ͑1994͔͒. Array masses between 120 and 2050 g/cm were used in these experiments. An analysis of the x-ray data taken using 24 wire arrays, shows a one-to-one correspondence between the observed kilo-electron-volt yields ͑5-64 kJ͒ and the fraction of initial array mass ͑0.3%-60%͒ that is radiating from the K shell. The 30 and 42 wire experiments demonstrated that tighter pinches with increased radiated powers were achieved with these larger wire number, improved symmetry arrays. In addition, increases in the implosion mass and array diameter in the 30 and 42 wire number cases resulted in increases in the radiated yield over the corresponding 24 wire shots, up to 88 kJ, which can be interpreted as due to improved coupling and thermalization of the kinetic energy. Moreover, spectroscopic analyses of the 30 and 42 wire experiments have shown that the increased wire numbers also resulted in K-shell radiating mass fractions of greater than 50%.

Compact wire array sources: power scaling and implosion physics.

“…The total Al K-shell yield was about 17 kJ at a load current of 5.5 MA (Table 3.1). Table 3.5 summarizes the results of the two Al 5056 planar array loads that have been fielded on Saturn (3688, 3748) as well as the cylindrical wire array from short-pulse Saturn with the highest published Al K-shell yield at 83 kJ [20]. More typical Al K-shell yields on Saturn are ≥ 60 kJ.…”

“…The range in η for planar arrays corresponds to assuming 100% or 50% mass participation in the implosion. [20]. Table 3.6.…”

“…In fact we obtained 5-6 MA in the 2008 planar array experiments. The Saturn short-pulse mode [20] typically exhibits a peak in the load current waveform at < 60 ns, and so while are able to access higher current, the implosion times are now significantly shorter than on Zebra or Z. However, the final data set extends over significant ranges of current, implosion time, and array width, and so we are able to extract fairly solid conclusions about power and yield scaling of multi-MA planar wire arrays as will be discussed.…”

“…For shot 14, E jxB is calculated from the η value in Ref. [20]. K-shell model parameters are calculated using c (Z = 13)=47, scaled from the Ar value in Ref.…”

Planar wire array performance scaling at multi-MA levels on the Saturn generator.

“…A high level of azimuthal symmetry (i.e. high wire number in a cylindrically symmetric configuration) is believed to be important in producing high x-ray powers as a symmetrical implosion produces a more uniform shell with smaller radial width, better convergence of the mass and current, and a higher level of mass participation in x-ray production [4,5].…”