SYMMETRICAL ALUMINUM-WIRE ARRAYS GENERATE HIGH-QUALITY Z-PINCHES AT LARGE ARRAY RADII

A Saturn-accelerator study of annular, aluminum-wire array, Z-pinch im plosions, in the calculated high-wire-number plasma-shell regime [Phys . Rev. Lett. 77, 5063 (1996)], shows that the radiated x-ray pulse wid th 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 radiation-magnetohydrodynamic code (E-RMHC) simulations in the r-z plane suggest that this pulse-width increase with radius is du e to the faster growth of the shell thickness (that arises from a two- stage development in the magnetic Rayleigh-Taylor instability) relativ e to the increase in the shell implosion velocity. Over the array radi i explored, the measured peak total x-ray power of similar to 40 TW an d energy of similar to 325 kJ show little change outside of a +/-15% s hot-to-shot fluctuation and are consistent with the E-RMHC simulations . Similarly, the measured peak K-shell (lines plus continuum) power of similar to 8 TW and energy of similar to 70 kJ show little change wit h radius. The minimal change in K-shell yield is in agreement with sim ple K-shell radiation scaling models that assume a fixed radial compre ssion for all initial array radii. These results suggest that the impr oved uniformity provided by the large number of wires in the initial a rray reduces the disruptive effects of the Rayleigh-Taylor instability observed in small-wire-number imploding loads. (C) 1998 American Inst itute of Physics. [S1070-664X(98)01510-9].