Tests of the hydrodynamic equivalence of direct-drive implosions with different D2 and He3 mixtures

Direct drive implosions of targets filled with different mixtures of D2 and He3 gas on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have shown an unexpected scaling of experimental nuclear yields. At temperatures above a few electron volts, D2 and He3 gases are fully ionized, and hydrodynamically equivalent fuels with different ratios of D2 and He3 can be chosen to have the same mass density, total particle density, and equation of state. Implosions with a 50/50 mixture of D:He3 by atom consistently result in measured nuclear yields half of that anticipated by scaling from measured yields of implosions with pure D2 and nearly pure He3. 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 DHe3), and for shock and compression yields. A number of possible mechanisms to cause the scaling are considered, but no dominant mechanism has been identified.