Measurements of three-dimensional instability growth of the imploding mass distribution for single and nested wire arrays*

Radiographic measurements at 6.151 keV show that the imploding mass distribution of a wire array z-pinch has the character of the magneto-Rayleigh Taylor instability [1]. Although the instability wavelength $\lambda $ and amplitude $\Delta $ are similar on either side of the z-pinch axis, detailed instability features (individual bubbles and spikes) are misaligned, which indicates a partly three-dimensional character, with some azimuthal incoherence. The temporal characteristics of the x-ray power are correlated with the instability amplitude near the axis at stagnation. Tailoring of the radial mass density profile of the z-pinches using current-transfer nested-arrays [2] and axial CH$_{2}$ foams leads to improved pulse compression, smaller amplitude $\Delta $ and x-ray powers of up to 220-240 TW. The data may support a self-similar spatio-temporal evolution with $\lambda \sim \Delta $ during part of the implosion. [1] D. B. Sinars et al., Phys. Plasmas [2005], [2] M. E. Cuneo, et al., Phys. Plasmas [2006]