Evolution of the structure of the dense plasma near the cross point in exploding wire X pinches

The dynamics of the dense plasma near the cross point of an X pinch has bee n investigated using 1 ns x-ray backlighting images at different moments re lative to the start of 100 ns [full width at half maximum (FWHM)] 200 kA cu rrent pulses. If the two metal wires are fine enough (e.g., 10 mu m W or 17 .5 mu m Mo) to form a pinch at the cross point, accompanied by an x-ray bur st, with the available current pulse, then the images show three stages of development: a radial explosion/expansion phase; an implosion during which a dense Z pinch of 200-300 mu m length forms at the cross point together wi th plasma jets which move axially away from that point; and a breaking up o f the Z pinch, coincident in time with one or two x-ray bursts, after which a 300 mu m gap opens up. For W, the backlighter minimum sensitivity is 10( 17)/cm(2) areal density, and the dense Z pinch is estimated to have a volum e density close to 10(21)/cm(3). Shock waves appear to be expanding at abou t 50 mu m/ns from the end points of the collapsing Z pinch, where the plasm a was the most dense. (C) 1999 American Institute of Physics. [S1070-664X(9 9)00307-9].