Wire core and coronal plasma formation and expansion in wire-array Z pinches with small numbers of wires have been studied on a 1 MA, 100 ns rise time pulsed power generator and a 500 kA, 50 ns generator. Two-frame point-projection x-ray imaging and three-frame laser optical imaging and interferometry were the principal diagnostic methods used for these studies. The x-ray images show that dense coronal plasma forms and is maintained close to each dense wire core in the array. A less dense, rapidly expanding (similar to 10 mu ms) coronal plasma, best seen in the laser images, surrounds the similar to 100 mu m radius dense corona. These results are in agreement with computer simulations and modeling carried out by Yu [Phys. Plasmas 14, 022705 (2007)]. Results are also presented for the dependence of the wire core and coronal plasma expansion rates on the wire diameter, number of wires and current through individual wires and the overall configuration for Al, Cu, and W wire arrays. For example, the W wire dense core expansion rate increases with increasing initial wire diameter from 5.1 mu m (0.1 mu ms) to 12.7 mu m diameter (0.3 mu ms). (C) 2007 American Institute of Physics.
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