Using Nuclear Data And Monte Carlo Techniques To Study Areal Density And Mix In D-2 Implosions

Measurements from three classes of direct-drive implosions at the OMEGA laser system [T. R. Boehly , Opt. Commun. 133, 495 (1997)] were combined with Monte Carlo simulations to investigate models for determining hot-fuel areal density (rhoR(hot)) in compressed, D-2-filled capsules, and to assess the impact of mix and other factors on the determination of rhoR(hot). The results of the Monte Carlo simulations were compared to predictions of simple, commonly used models that use ratios of either secondary (DHe)-He-3 proton yields or secondary DT neutron yields to primary DD neutron yields to provide estimates rhoR(hot,2p) or rhoR(hot,2n), respectively, for rhoR(hot). For the first class of implosion, where rhoR(hot) is low (less than or equal to3 mg/cm2), rhoR(hot,2p) and rhoR(hot,2n) often agree with each other and are often good estimates of the actual rhoR(hot). For the second class of implosion, where rhoR(hot) is of order 10 mg/cm2, rhoR(hot,2p) often underestimates the actual value due to secondary proton yield saturation; in addition, fuel-shell mix causes rhoR(hot,2p) to further underestimate, and rhoR(hot,2n) to overestimate, rhoR(hot). As a result, values of rhoR(hot,2p) and rhoR(hot,2n) can be interpreted as lower and upper limits, respectively. For the third class of implosion, involving cryogenic capsules, secondary protons and neutrons are produced mainly in the hot and cold fuel regions, respectively, and the effects of the mixing of hot and cold fuel must be taken into account when interpreting the values of rhoR(hot,2p) and rhoR(hot,2n). From these data sets, it is concluded that accurate inference of rhoR(hot) requires comprehensive measurements and detailed modeling. (C) 2005 American Institute of Physics.