Ignition and target gain at the National Ignition Facility

Alex Zylstra (for the NIF Team)

Thermonuclear fusion in the laboratory is a scientific grand challenge, a highly compelling problem because the fusion reactions can self-heat the fuel and continue the burn. Predominantly approaches use the fusion of deuterium and tritium nuclei, which generates 17.6 MeV of energy released in a neutron and alpha particle. The alpha particle, which carries 1/5 of the energy, can heat the plasma. A plasma in which the alpha self-heating is greater than external heating is termed a ‘burning plasma’, and one in which the self-heating dominates over all loss mechanisms, leading to a run-away increase in temperature, is termed ‘ignited’. Inertial confinement fusion (ICF) has pursued these scientific milestones using large laser drivers, notably the National Ignition Facility (NIF) at LLNL. Here we use the laser energy, up to 2.05 MJ, to generate a hot x ray bath, which creates ablation pressures of hundreds of Mbar at the outer surface of a fuel-containing capsule. The ablation pressure implodes the capsule, with fuel pressures of several hundred GBar generated as the fuel stagnates at the center to initiate fusion burn. In recent years several improvements in the scientific design and requisite technologies have enabled increasing performance of NIF experiments through the burning plasma and ignition regimes, which are prerequisites for high gain in inertial fusion, to the first experiment with target gain exceeding unity. *Work performed under the auspices of the U. S. Department of Energy by LLNL under contract DE-AC52-07NA27344. LLNL-ABS-845054