Signatures of hot-spot asymmetries in secondary DT neutron spectra in NIF implosions

To achieve ignition, Inertial Confinement Fusion (ICF) implosions must converge symmetrically as any asymmetries can have deleterious effects on the implosion performance. As such, the measurement of asymmetries has long been an important tool for assessing and improving the performance of ICF implosions. Traditionally this has been accomplished through a combination of neutron and x-ray imaging and neutron down-scatter measurements. On the NIF, surrogate D$_{\mathrm{2}}$ and D$^{\mathrm{3}}$He filled implosions are often used, for reasons of practicality, in place of fully integrated DT layered experiments. These experiments lack the performance required for neutron imaging and must rely entirely on x-ray imaging to measure implosion asymmetries. However, directional neutron spectra from secondary DT reactions also encode information about implosion symmetry, opening the door for alternative and complementary asymmetry measurements. In this work, we demonstrate this capability using four neutron time of flight spectrometers on the NIF. This work was supported in part by the U.S. DOE, the MIT/NNSA CoE, and LLNL.