Impact of flows on ion temperatures inferred from neutron spectra produced in NIF DT implosions

Neutron spectrometers on the NIF provide accurate, directional information of the DT and DD neutron spectra from layered DT implosions. Traditionally, ion temperatures ($T_{ion})$, essential for assessing conditions in the hotspot of the implosions, are inferred from the broadening of primary neutron spectra. Directional motion (flow) of the fuel at burn also impacts broadening and may lead to artificially inflated ``$T_{ion}$'' values. We examine NIF neutron spectra to assess the impact of flows on measured $T_{ion}$. Measured DT $T_{ion}$ is consistently higher than measured DD $T_{ion}$, which suggests that significant energy is lost to radial or turbulent kinetic fuel motion at peak burn. However, explaining the full observed $T_{ion}$ difference with fuel motion, as calculated from a Ballabio\footnote{Ballabio et al., Nucl. Fusion \textbf{38}, 1723 (1998).} and Murphy\footnote{Murphy, Phys. Plasmas \textbf{21}, 072701 (2014).} analysis, leads to a thermal $T_{ion}$ too low to explain observed yields. These results have improved our understanding of hotspot formation and the concept of ``stagnation'' in layered NIF implosions.