Radius scaling effects in nickel wire array Z-pinches

Abstract

Nickel wire arrays of different masses and initial diameters have been imploded on the DNA/Double-EAGLE generator. Array masses and diameters were chosen to cause an implosion 10 to 20 ns before the peak current of 4 MA. The nickel L-shell radiated yield around 1 keV was found to be maximized at 35 kJ for an initial array diameter of 15 mm and a mass loading of 86 μg/cm. X-ray diagnostic data indicate that the 1-keV L-shell yield is maximized when the array diameter and mass are such that the implosion energy is just sufficient to thermalize on axis to a 3-mm diameter bulk plasma. This plasma is predominantly ionized into the L-shell with an ion density of 10 19 cm -3 and an electron temperature of 450 eV. Initial diameters larger than optimum result in hotter lower density plasmas. The reduced density causes a reduction in the yield. By contrast, for diameters less than optimum, the bulk thermalized plasma is too massive and too cold for efficient radiation from the L-shell. Localized “hot spots” do emit L-shell radiation, and consequently the total L-shell yield does not fall as precipitously with decreasing array radius as might be expected from the change in the bulk plasma parameters.