Symmetric aluminum-wire arrays generate high-quality Z pinches at large array radii

Abstract

A Saturn-accelerator study of annular, aluminum-wire array, Z-pinch implosions, in the calculated high-wire-number plasma-shell regime ͓Phys. Rev. Lett. 77, 5063 ͑1996͔͒, shows that the radiated x-ray pulse width increases from about 4 nsec to about 7 nsec, when the radius of the array is increased from 8.75 to 20 mm at a fixed array mass of 0.6 mg. Eulerian radiationmagnetohydrodynamic code ͑E-RMHC͒ simulations in the r-z plane suggest that this pulse-width increase with radius is due to the faster growth of the shell thickness ͑that arises from a two-stage development in the magnetic Rayleigh-Taylor instability͒ relative to the increase in the shell implosion velocity. Over the array radii explored, the measured peak total x-ray power of ϳ40 TW and energy of ϳ325 kJ show little change outside of a Ϯ15% shot-to-shot fluctuation and are consistent with the E-RMHC simulations. Similarly, the measured peak K-shell ͑lines plus continuum͒ power of ϳ8 TW and energy of ϳ70 kJ show little change with radius. The minimal change in K-shell yield is in agreement with simple K-shell radiation scaling models that assume a fixed radial compression for all initial array radii. These results suggest that the improved uniformity provided by the large number of wires in the initial array reduces the disruptive effects of the Rayleigh-Taylor instability observed in small-wire-number imploding loads.

Wire array Z-pinch insights for enhanced x-ray production

“…The E-RMHC simulations show that over the mass-and radius-range measured, which spanned an implosion time of 40 to 90 ns, the shape of the simulated total-radiated-power pulse tracks the initial pulse measured [12,13). Moreover, the implosion time of the simulated pulse agrees with that measured, within a shot-to-shot variation of only 2 ns.…”

“…These simulations simultaneously generate a second quasi-convergence as shown in Figs. 10A and 10B. The use of the nominal electron-,* photon coupling in the E-RMHC simulations is denoted by E-RMHC:N. Radiation pulseshapes at the first peak, however, using either coupling agree with one another [12], and thus indicate that (aside from the double bounce, which is sensitive to the coupling) the dynamics creating the puiseshape of the first pulse are relatively independent of the radiation emission, in these simulations.…”

“…1lC and 11D). In the second series, the array mass was held fixed, near a value which maximized the peak power from the first series, and the array radius was varied [13]. This series showed that when the radius is increased from 8.6 to 20 mm, for a mass of 0.6 mg in 136 wires, the total radiated pulsewidth (Fig.…”

“…These experiments were designed to better understand the conditions that optimize the total radiated power in this regime [41]. In the first series, the radius was held fixed at 12 mm and the mass was varied over the range 0.42 to 3.4 mg [12]. This series showed that when the .…”

“…Importantly, the intense radiation generated from the high wire-number pinches is used to test radiation-drive geometries relevant to the ICF program [7,8], such as in the static hohlraum concept of Olson [9,10] or the dynamic hohlraum concept described in Ref. 10 by Nash, Derzon, Chandler et al In this manuscript, changes in total radiated x-ray power as a function of wire number [11], array mass [12], and load radius [13], generated from Saturn experiments with imploded 20-mm-long aluminum-wire arrays that led to these breakthrough hohlraum results are reviewed and contrasted with models and simulations. Because much of the wire-number analysis is new, this material is emphasized.…”