Signatures of systematic azimuthal asymmetry in nuclear diagnosis of ICF implosions on the NIF

In ICF experiments on the NIF, several nuclear diagnostics provide information about the state of the converged hotspot and fuel near peak convergence. Net velocity of the fusing plasma is diagnosed by Neutron Time-of-Flight (NTOF) diagnostics via Doppler shifts in the primary DT-neutron peak energy; asymmetry of the converged DT fuel areal density (ρR_fuel) is diagnosed by Nuclear Activation Diagnostics (NADs) that record differences in neutron fluence with position due to scattering in the fuel. On recent implosions using high-density carbon (HDC) ablators, both high net hotspot velocities (> 50 km/sec) and large mode-1 ρR asymmetries (> 25%) have been inferred. In these experiments, the direction of hotspot flow coincides with the direction of minimum ρR, and across many experiments this direction clusters preferentially toward one half of azimuthal space in the NIF geometry (φ = 0˚—180˚). These results are consistent with a persistent, unintentional azimuthal drive asymmetry or offset on this series of implosions. Results from various campaigns will be compared and the effect on ICF ignition will be discussed.