Scaling of plasma temperature, density, size, and x-ray emission above 1 keV with array diameter and mass for aluminum imploding-wire plasmas.

Abstract

A series of five aluminum imploding-wire experiments were performed to investigate the dependence of plasma temperature, density, size, and x-ray emission above 1 keV on the initial wire-array diameter and mass per unit length. The plasmas were created by imploding cylindrical arrays of fine wires with the Blackjack 5 pulse generator. In these experiments the array diameter and mass per unit length were varied by factors of 2 and 4.5, respectively. The electron temperatures were determined from the slope of the free-to-bound continuum, the intensity ratios of selected x-ray-emission lines and strength of the continuum edges. The line ratios were interpreted by means of a collisional radiative equilibrium model. Plasma ion densities were obtained from the total x-ray emission above 1 keV. The size of the plasma that emits above 1 keV was inferred from x-ray pinhole photographs and from measurements of the line broadening caused by the finite source size. As the initial diameter of the wire array was increased, the array mass was decreased in order to maintain constant implosion time and optimum energy coupling from the pulse generator to the load. The larger-diameter, lower-mass arrays produced larger-diameter, higher-temperature, lower-density plasma pinches. With the simultaneous increase in array diameter and decrease in array mass, the electron temperature increased from 0.5 to 0.8 keV, the ion density decreased from 4\ifmmode\times\else\texttimes\fi{}${10}^{19}$ to 0.13\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, the diameter of the plasma column increased from 1.2 to 5.5 mm, and the x-ray emission above 1 keV decreased from 20 to 0.45 kJ.