MEASUREMENTS OF NEUTRON-SPECTRA FROM NOVA TARGETS

We have measured neutron spectra from targets on the Nova laser. The t hree basic classes of targets are (1) directly driven capsules with ab lative or exploding pushers, (2) indirectly driven imploding capsules with Various hohlraum drives, capsule thicknesses, capsule fill pressu res, and hohlraum gas fills, and (3) gas-filled hohlraums containing d euterated gas mixtures. In many capsule implosions, the neutron spectr a are significantly broader than predictions of fusion-reaction-weight ed ion temperatures from simulations. For implosions of deuterated cap sules filled with H-2, the observed spectra are consistent with the pr edicted combination of thermal and motional broadening. For normal cap sules filled with D-2, we conjecture that implosion asymmetries may in duce fluid motion within the compressed fuel which contributes to the measured spectral width, but not the fusion reactivity, and which is n ot included in the simulations. (C) 1997 American Institute of Physics .