Z-pinch discharges in aluminum and tungsten wires

A series of experiments on Z-pinch plasmas, driven by a pulsed power genera tor that delivers 160 kA with a rise time (10%-90%) of 65 ns are reported. Tungsten wires of various diameters were used and results are compared with 15 mu m diameter aluminum wire. The expansion of the pinch is studied as a function of wire diameter and material. Schlieren observations show that t he coronal plasma of various diameters of tungsten wires expands with the v elocity of (9.4+/-1.0) x 10(3) m/s. The aluminum pinch expands at least a f actor of 2 faster. The m=0 perturbations appear at about 8 ns for the alumi num compared with 20 ns for the tungsten pinch. The wavelength and diameter of the perturbations increase with time for both types of wires, and relat ively faster for the aluminum pinch. The short wavelength perturbations (si milar to 200 mu m) persist for a longer time for larger diameter tungsten w ires. Bright spots are seen to appear after 60 ns from the current start fo r tungsten wires, whereas for aluminum wires, bright spots appear after 40 ns. The decay time of bright spots is 40 ns for the smallest diameter tungs ten wire compared with only a few nanoseconds for larger diameter wires. Ha rd x-ray emission above 6 keV was observed from tungsten wire pinches, but it was not observed from either bright spots or the plasma column for the a luminum pinch. However, hard x-ray emission from the anode due to an electr on beam was observed for wires of both materials. (C) 1999 American Institu te of Physics. [S1070-664X(99)03506-5].