Signatures of azimuthal plasma asymmetries in the secondary DT neutron spectra of magnetized implosions at the NIF

Secondary DT neutrons have proven to be an important diagnostic for magnetized implosions using D2 fuel both at the Z facility [1] and the NIF [2]. These neutrons are generated from 1 MeV D(D,p)T tritons streaming through the background plasma and are sensitive to the burn-averaged density, temperature, and magnetic fields in the hot spot. Core magnetic fields of ~ 5 kT, arising from the compressed externally applied seed field, can strongly impact the paths of these tritons which is reflected in the resultant secondary neutron spectra. Recent magnetized implosion experiments on the NIF have generated skewed equatorial secondary DT neutron spectra not seen in previous experiments. This skew implies some significant azimuthal asymmetry in the conditions probed by the tritons. We use 3D Monte-Carlo modeling as well as mix inferences from x-ray imaging to investigate potential explanations for the observed skews, including suppression of fill-tube mix. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344 and LDRD project SI-2020-002.



1. P. F. Schmit et al., Phys. Rev. Lett. 113, 155004 (2014).

2. J. D. Moody et al., submitted to Phys. Rev. Lett.