ASYMMETRY AND MIX IN DIRECT-DRIVE ICF EXPERIMENTS

摘要

In order to measure the coupling of mix to asymmetry in ICF implosions, we have performed experiments on the OMEGA laser that vary the energy of each of the sixty beams individually to achieve a given fraction of P2, the second-order Legendre polynomial, on the laser drive. Simultaneous X-ray and pinhole neutron images of the asymmetric implosions were obtained. The X rays primarily give information about the glass shell, whereas the neutrons image the core of the implosion. Mathematical reconstruction of the neutron images enhances the resolution beyond that produced by the point-spread function of the pinhole. Comparison of experiment to code illuminates the mechanisms of mix. The code predicts that the decline of neutron yield with asymmetry is independent of yield degradation caused by mix. The experiments validate this premise. Simulations of both X-ray and neutron images are well matched by the data.