Tests of the hydrodynamic equivalence of direct-drive implosions with different D2 and 3He mixtures

Direct drive implosions of targets filled with different mixtures of D-2 and He-3 gas on the OMEGA laser system [T. R. Boehly , Opt. Commun. 133, 495 (1997)] have shown an unexpected scaling of experimental nuclear yields. At temperatures above a few electron volts, D-2 and He-3 gases are fully ionized, and hydrodynamically equivalent fuels with different ratios of D-2 and He-3 can be chosen to have the same mass density, total particle density, and equation of state. Implosions with a 50/50 mixture of D:He-3 by atom consistently result in measured nuclear yields half of that anticipated by scaling from measured yields of implosions with pure D-2 and nearly pure He-3. This observation is seen over a wide range of experimental configurations, including targets with a variety of shell thicknesses and fill pressures, simultaneously for two different nuclear yields (DD and (DHe)-He-3), and for shock and compression yields. A number of possible mechanisms to cause the scaling are considered, but no dominant mechanism has been identified. (c) 2006 American Institute of Physics.