Use of linear wire array Z pinches to examine plasma dynamics in high magnetic fields

Planar arrangements of tungsten wires, with a flat, closely positioned current return surface, were driven by the Magpie generator (1 MA,240 ns) [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1553 (1996)]. This “linear array” configuration was expected to increase the magnetic field and forces experienced by the wires to the same level as created in experiments at the 20 MA Z facility. The wires in the linear array ablated, on average, (5–6)× faster than in 1 MA cylindrical array experiments—consistent with the expected increase in force at the wires. Streams of coronal plasma flowed from the wires to form a precursor column offset from the plane of the linear array. The dynamics of the column suggested that a much larger fraction of current flowed through it than in cylindrical array experiments (∼20%–30% cf. <7%). Inductance determined the division of current between the wires of the array; the lower inductance edge wires experienced higher currents and magnetic fields than the center wires, further increasing the ablation rate of the edge wires, resulting in an earlier start to their implosion. Timing of the implosion provided evidence that the “ablation velocity” of plasma in an array does not change with the level of drive current.