Analysis of the First NIF Neutron Images

Neutron imaging at the National Igntion Facility obtained its first images from both directly laser driven and X-radiation driven implosions. A directly driven DT filled glass microballoon gave an oblate image (P2/P0=-45{\%}) whose size (P0=70$\mu $m) fit within the X-ray images. Simulations using the polar direct drive laser pointing give a round image of P0 $\sim $95$\mu $m. However as the electron flux limiter is reduced from 0.06 to 0.03 the image becomes oblate. The observed asymmetry can be reproduced by transferring $\sim $10{\%} of the energy from the outer laser beams to the inner. Radiation driven implosions of ignition capsules with 20{\%}D, and 50{\%}D produced $\sim $ 30$\mu $m radius oblate images in 12-15 MeV neutrons. Images in 10-12 MeV neutrons, which have experienced one scattering in the fuel and number $\sim $ 4{\%} of the primaries, showed larger images ($\sim $44-56 $\mu $m). Image sizes indicate the compression of the fuel and are consistent with observed 10-12/13-15MeV yield ratios. Work funded by the USDOE at LANL, LLNL, NSTEC and LLE.