Effect of discrete wires on the implosion dynamics of wire arrays

Summary form only given. The 3-D topology of the magnetic field in wire array z-pinches, combined with the core-corona structure of the plasma formed from the wires, results in the implosion dynamics being significantly different from the implosion of a thin plasma shell. A phenomenological model of wire array Z-pinch implosions, based on the analysis of experimental data obtained on the MAGPIE generator will be presented. The data show that during the first /spl sim/80% of the implosion the wire cores remain stationary in their initial positions, while the coronal plasma is continuously flowing from the wire cores to the array axis. This phase of implosion ends when gaps in the wire cores are formed, which occurs due to non-uniformity of the ablation rate along the wires. After formation of the gaps a rapid snowplough implosion of the precursor plasma, previously injected in the interior of the array, occurs. The radial density distribution of the precursor plasma at the start of this final implosion phase is peaked on the axis, which improves stability of the implosion. It is possible that the highest powers of the X-ray pulse are obtained in this implosion scenario, without merging of the wires into a thin shell, as this is less prone to the development of the Rayleigh-Taylor instability than the shell-like implosions. The model suggests modified "initial" conditions for 2-D (r-z plane) radiative-MHD codes and a possible scaling of the model to larger drive currents and array diameters will be discussed. The experimental data on the formation of the precursor plasma flow in wire arrays and interaction of this plasma with foam targets will be also presented.