The dynamics of single and nested nickel wire array Z pinch implosions

Experiments on the implosion dynamics of single and nested nickel wire arrays driven by the MAGPIE generator with a 1-MA, 240-ns current pulse are reported. Like aluminum and tungsten wire discharges, the plasma formed from individual wires has a core-corona structure. In a single nickel array, a wire core size of 75 μm before the implosion was measured by X-ray radiography. The precursor plasma is formed on axis and is m=1 unstable. The implosion of the array occurs later than predicted by the 0-D model, indicating that a fraction of current flows through the precursor plasma. This is in contrast with copper arrays (copper has the similar radiation properties as nickel, Z_nickel=28, Z_copper=29) where the precursor plasma is uniform and implosion time is as predicted by 0-D model. Experiments with nickel nested arrays show that the expansion of the wires in the outer and the inner array is similar and a precursor plasma is formed on the axis earlier than in single arrays. It appears from the experimental data that a significantly larger fraction of the current is flowing through the inner array.