Current scaling of optimum K-shell X-ray yield and load mass applied to argon gas-puff Z-pinches

Abstract

Summary form only given, as follows. A simple radiation-scaling model based on two-level atomic physics and plasma energy balance was developed to guide selection of load parameters and estimate K-shell x-ray yields for z-pinch drivers. The model agrees with neon gas-puff experiments at 0.7 MA and aluminum wire-array experiments at 7 MA. It predicts the current scaling of peak K-shell yield from optimum load parameters for Ar gas-puffs. Results are compared with data spanning an order-of-magnitude current variation, including recent results on Z at 15 MA. Optimum temperature and mass are determined by maximizing K-shell yield subject to energy balance, fixed implosion time, and fixed compression ratio, resulting in peak yield and optimum mass as functions of implosion energy and stagnation radius. Current scalings result from the implosion energy vs current, implosion-time scaling, and compression ratio that best fit Double Eagle nested-shell argon results. In light of the wide variety of driver and load configurations sampled, it is noteworthy that both the maximum-yield and optimum-mass scalings provide respectable absolute-value fits to the data, including the implosion-time dependence. The yield smoothly varies from the expected I/sup 4/ to I/sup 2/ dependence as the current increases, with the center of the transition at 5 MA. The optimum mass is proportional to I/sup 2/ for low currents and transitions to I/sup 12/, in agreement with the I/sup 2/ 15 MA data. The lower-than-expected predicted mass for I radiators should be considered in the design of loads with atomic numbers 10 to 18.