K-shell X-ray performance and load risk projections for future super-power generators

Summary form only given. During the past two decades, 100-ns-duration pulsed power has been used to produce intense sources of K-shell X-radiation from the z-pinch implosion of high-atomic-number annular gas-puff and wire-array loads. For initial annular radii of a few cm or less, and currents in the 0.5- to 10-MA range, experimental K-shell yields are in factor-of-two agreement with low-dimensional modeling of the implosion dynamics and radiation processes. For initial radii larger than a few cm, experiments indicate a reduction in K-shell yield, likely associated with multi-dimensional instability and asymmetry effects. However, efficient K-shell emission from long-implosion-time or high-photon-energy loads requires large radii. For the 300-ns current-rise-time DSWA DECADE driver, large radii are required for sufficient implosion velocities to excite the argon K-shell in 200- to 300-ns implosions. For 100-ns implosions on the proposed SNL X-1 base-line driver, large radii are required to achieve very high implosion velocities for excitation of X-rays in the several-10s-of-keV regime. For such cases, both K-shell yield and the associated load risk increase strongly with radius. Were, a simple two-level model for K-shell scaling, coupled to a circuit model driving a slug-model implosion, and benchmarked against experiments on Hawk, Saturn, and Z, is used to estimate yield as a function of load radius, and therefore risk, for future drivers. The increased yield at smaller radius (and reduced load risk) provided by a reduced current rise time (at increased pulsed power risk) is also quantified. The approach presented here demonstrates a simple tool useful to experimentalists and pulsed power designers who wish to estimate within about a factor-of-two how K-shell radiation scales with generator and load parameters.