Fusion Energy Output Greater than the Kinetic Energy of an Imploding Shell at the National Ignition Facility

TLDR

The experiments used a 1.5‑MJ, 7.5‑ns three‑shock laser pulse on high‑density carbon ablators in low‑gas‑filled helium, irradiating bare depleted‑uranium hohlraums to a peak radiative temperature of ~290 eV, driving the DT shell to ~380 km s⁻¹ and ~21 kJ kinetic energy. These shots produced fusion energy twice the shell’s peak kinetic energy, yielding 54 kJ of output, a neutron yield of 1.9 × 10¹⁶, and unprecedented hot‑spot areal density (~0.3 g cm⁻²) and stagnation pressure (~360 Gbar) after controlling low‑mode asymmetries.

Abstract

A series of cryogenic, layered deuterium-tritium (DT) implosions have produced, for the first time, fusion energy output twice the peak kinetic energy of the imploding shell. These experiments at the National Ignition Facility utilized high density carbon ablators with a three-shock laser pulse (1.5 MJ in 7.5 ns) to irradiate low gas-filled ($0.3\text{ }\text{ }\mathrm{mg}/\mathrm{cc}$ of helium) bare depleted uranium hohlraums, resulting in a peak hohlraum radiative temperature $\ensuremath{\sim}290\text{ }\text{ }\mathrm{eV}$. The imploding shell, composed of the nonablated high density carbon and the DT cryogenic layer, is, thus, driven to velocity on the order of $380\text{ }\text{ }\mathrm{km}/\mathrm{s}$ resulting in a peak kinetic energy of $\ensuremath{\sim}21\text{ }\text{ }\mathrm{kJ}$, which once stagnated produced a total DT neutron yield of $1.9\ifmmode\times\else\texttimes\fi{}{10}^{16}$ (shot N170827) corresponding to an output fusion energy of 54 kJ. Time dependent low mode asymmetries that limited further progress of implosions have now been controlled, leading to an increased compression of the hot spot. It resulted in hot spot areal density ($\ensuremath{\rho}\mathrm{r}\ensuremath{\sim}0.3\text{ }\text{ }{\mathrm{g}/\mathrm{cm}}^{2}$) and stagnation pressure ($\ensuremath{\sim}360\text{ }\text{ }\mathrm{Gbar}$) never before achieved in a laboratory experiment.