Modeling and performance predictions of double-shell gas puffs on double eagle and decade quad

Summary form only given, as follows. The design of gas flow nozzles for optimum K-shell X-ray emission remains an imperfect science. We report on a limited set of tests, using the Double Eagle simulator, evaluating two key factors. The first factor was the detailed form of the nozzle contours: simple linear contours versus curved aerodynamic contours intended to minimize turbulence. The second factor was the relative radial concentration of mass in the flow. All tests employed double shell nozzles. While the test set was incomplete, the data strongly imply that details of nozzle shape are relatively unimportant. On the other hand, radial mass distribution is very critical. With twice the mass (/spl mu/g/cm) in the outer shell than the inner shell, argon K-shell yield was only 5 kJ. With nearly equal masses in the two shells, yield increased dramatically to over 17 kJ, matching the optimum output on Double Eagle for 200 ns implosions. Since the simplest models of Z-pinches favor putting most of the mass at the largest radius, these results strongly imply that that configuration is subject to severe disruption by instabilities during the implosion. These results confirm earlier observations (Coleman et al., 2001) that filled-in mass distributions are preferred, and support the concept of snowplow stabilization.