Design of inertial fusion implosions reaching the burning plasma regime

TLDR

A burning plasma state is achieved when alpha particles from deuterium–tritium fusion redeposit their energy, becoming the dominant heating source. The experiments employ a laser‑generated hohlraum to spherically implode deuterium–tritium capsules, with symmetry enhanced by redistributing laser energy among beams and using advanced hohlraum geometry. These design improvements produced a burning plasma at the National Ignition Facility, delivering 1.5 petawatts of fusion power and 170 kJ of energy, with simulations confirming alpha‑particle heating dominates the hot‑spot energy balance.

Abstract

Abstract In a burning plasma state 1–7 , alpha particles from deuterium–tritium fusion reactions redeposit their energy and are the dominant source of heating. This state has recently been achieved at the US National Ignition Facility 8 using indirect-drive inertial-confinement fusion. Our experiments use a laser-generated radiation-filled cavity (a hohlraum) to spherically implode capsules containing deuterium and tritium fuel in a central hot spot where the fusion reactions occur. We have developed more efficient hohlraums to implode larger fusion targets compared with previous experiments 9,10 . This delivered more energy to the hot spot, whereas other parameters were optimized to maintain the high pressures required for inertial-confinement fusion. We also report improvements in implosion symmetry control by moving energy between the laser beams 11–16 and designing advanced hohlraum geometry 17 that allows for these larger implosions to be driven at the present laser energy and power capability of the National Ignition Facility. These design changes resulted in fusion powers of 1.5 petawatts, greater than the input power of the laser, and 170 kJ of fusion energy 18,19 . Radiation hydrodynamics simulations 20,21 show energy deposition by alpha particles as the dominant term in the hot-spot energy balance, indicative of a burning plasma state.