The dynamics of wire array Z-pinch implosions

Wire array Z-pinch dynamics are studied in experiments with 16-mm diameter arrays of between 8 and 64, 15-mu m diameter aluminum wires, imploded in 20 0-260 ns by a 1.4-MA current pulse. Side-on laser probing shows early devel opment of noncorrelated m=0-like instabilities with an axial wavelength sim ilar to 0.5 mm in individual wires. End-on interferometry (r-theta plane) s hows azimuthal merging of the plasma with a density of 10(17) cm(-3) in 90- 65 ns for 8-64 wires, respectively. At the same time low-density plasma rea ches the array axis and forms a precursor pinch by 120-140 ns. At 0.7-0.85 of the implosion time a global m=0 instability with a wavelength of 1.7-2.3 mm was detected in soft x-ray gated images, laser probing, and optical str eaks. The time when the instability reaches the observable level correspond s to the number of e-foldings for the growth of the classical Rayleigh-Tayl or instability of integral gamma dt similar to 5.6-7. The scaling of this n umber with the number of wires is consistent with the instability growth fr om the seed level determined by the averaging of uncorrelated density pertu rbations in individual wires. Preliminary results from a 4X4 array permit t he simultaneous observation by laser probing of the characteristic bubble a nd spike structure of the magneto Rayleigh-Taylor instability. (C) 1999 Ame rican Institute of Physics. [S1070-664X(99)90705-X].