Wire core and coronal plasma expansion in wire-array Z pinches with small numbers of wires

Abstract

Wire core and coronal plasma formation and expansion in wire-array Z pinches with small numbers of wires have been studied on a 1MA, 100ns rise time pulsed power generator and a 500kA, 50ns 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 (∼10μm∕ns) coronal plasma, best seen in the laser images, surrounds the ∼100μm radius dense corona. These results are in agreement with computer simulations and modeling carried out by Yu et al. [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 5.1μm (0.1μm∕ns)to12.7μm diameter (0.3μm∕ns).