Onset of Hydrodynamic Mix in High-Velocity, Highly Compressed Inertial Confinement Fusion Implosions

TLDR

Inertial confinement fusion experiments on the National Ignition Facility have achieved deuterium‑tritium yields of 0.8–7×10¹⁴ and fuel areal densities of 0.7–1.3 g cm⁻². The study aims to quantify hydrodynamic instability mix of the ablator into the hot spot by measuring its elevated absolute x‑ray emission. Implosions employed hohlraums irradiated with shaped 1.5–1.9 MJ laser pulses, varying peak power, duration, ablator dopant concentrations, and shell thicknesses to assess mix. DT neutron yield and ion temperature drop abruptly when hot‑spot mix mass exceeds several hundred ng, and radiation‑hydrodynamic modeling points to low‑mode asymmetries and increased ablator surface perturbations as likely causes.

Abstract

Deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility have demonstrated yields ranging from 0.8 to 7×10(14), and record fuel areal densities of 0.7 to 1.3 g/cm2. These implosions use hohlraums irradiated with shaped laser pulses of 1.5-1.9 MJ energy. The laser peak power and duration at peak power were varied, as were the capsule ablator dopant concentrations and shell thicknesses. We quantify the level of hydrodynamic instability mix of the ablator into the hot spot from the measured elevated absolute x-ray emission of the hot spot. We observe that DT neutron yield and ion temperature decrease abruptly as the hot spot mix mass increases above several hundred ng. The comparison with radiation-hydrodynamic modeling indicates that low mode asymmetries and increased ablator surface perturbations may be responsible for the current performance.