Z-pinch discharges in aluminum and tungsten wires

A series of experiments on Z-pinch plasmas, driven by a pulsed power generator 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 the coronal plasma of various diameters of tungsten wires expands with the velocity of (9.4+/-1.0) x 10(3) m/s. The aluminum pinch expands at least a factor of 2 faster. The m=0 perturbations appear at about 8 ns for the aluminum compared with 20 ns for the tungsten pinch. The wavelength and diameter of the perturbations increase with time for both types of wires, and relatively faster for the aluminum pinch. The short wavelength perturbations (similar to 200 mu m) persist for a longer time for larger diameter tungsten wires. Bright spots are seen to appear after 60 ns from the current start for 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 tungsten wire compared with only a few nanoseconds for larger diameter wires. Hard 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 aluminum pinch. However, hard x-ray emission from the anode due to an electron beam was observed for wires of both materials. (C) 1999 American Institute of Physics. [S1070-664X(99)03506-5].