Diagnosing effects of laser-drive asymmetry on hot-spot flow dynamics and implosion performance on NIF*

Asymmetries in laser indirect drive during inertial confinement fusion implosions dramatically reduce performance due to energy transfer into residual capsule motion and thus lost from hot spot heating. Dedicated experiments on the National Ignition Facility were recently performed which characterized these effects. This investigation kept capsule, fuel, and hohlraum features identical while varying the balance of laser energy entering each end of the hohlraum. Flow velocities >130 km/s in the imbalanced cases were observed using neutron time-of-flight techniques and corroborated by neutron activation detectors. Variance in these bulk flows contributes to apparent ion temperatures and exhibits a cosine dependence on the angle between observations and flow direction. Distinct regions of peak x-ray and neutron emission are seen within the capsule, with brightened limbs in the P1-driven direction. Time-resolved x-ray imaging reveals fill-tube dynamics and suggests internal flow-fields during the implosion. Results from this set of shots will be presented, and comparison with simulations discussed.