Continued development of a 12-cm-diameter nozzle for argon Z-pinches

We report on the variation of K-shell X-ray output of an argon Z-pinch as a function of the radial gas distribution. The tests, conducted on the Double-EAGLE simulator at ∼3.5-MA peak current, utilized a 12-cm-diameter double-shell nozzle that was designed for use with the 300-ns rise-time current pulse (∼6 MA) of the DECADE QUAD pulsed power machine. By varying the plena gas pressures of the inner and outer shells, the net radial distribution could be changed from one that was strongly concentrated near the axis to one more broadly distributed as a function of radius. Previous work has shown that a roughly uniform radial distribution gives higher X-ray output than shell-like flows for gas Z-pinches. The present work was focused on refining the optimum radial distribution and to establish benchmarks for modeling calculations. The present data show that the K-shell yield has a broad optimum (and the relative strength of the K continuum >4 keV systematically changes) as the mass distribution becomes more peaked near the axis. Very-high-quality K-emitting volumes (<5 ns pulse width from <1 mm diameters) were achieved over a significant fraction of the pinch length.