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 been investigated using 1 ns x-ray backlighting images at different moments relative to the start of 100 ns [full width at half maximum (FWHM)] 200 kA current 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 burst, 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 with plasma jets which move axially away from that point; and a breaking up of 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 volume density close to 10(21)/cm(3). Shock waves appear to be expanding at about 50 mu m/ns from the end points of the collapsing Z pinch, where the plasma was the most dense. (C) 1999 American Institute of Physics. [S1070-664X(99)00307-9].