The effect of current prepulse on wire array Z-pinch implosions

The effect of a prepulse current on the behavior of wire array Z pinches is investigated. The experiments were performed on the MAGPIE generator (1 MA peak current at 240 ns) [I. Mitchell, J. M. Bayley, J. P. Chittenden , Rev. Sci. Instrum. 67, 1533 (1996)]. A linear ramp current, similar to 500-ns long, was used as a prepulse. The array consisted of 32 15-mum aluminum wires, 23-mm long arranged in a 16-mm diameter circle. With a prepulse of 1 kA/wire, a low density precursor plasma column (n(e)similar to 2x10(17) cm(-3)) is formed on the array axis before the start of the main current. Later, the soft x-ray emission shows the growth of an m=1 helical instability in the precursor plasma, which indicates the presence of a current. Without a prepulse current, the precursor plasma on axis is uniform and does not show any instability. The x-ray pulse at stagnation on axis is at least 30 times smaller with a prepulse current than without. (C) 2002 American Institute of Physics.