The inertial confinement fusion principle attempts to compress a small deuterium-tritium pellet to the density and temperature required for fusion ignition in its centre. The reaction then takes place before the pellet remnants are blown apart, so the fusion plasma is held together only by its own inertia. There are two means of inertial confinement fusion: direct drive, in which laser beams strike the surface of the pellet, and indirect drive, in which laser beams generate strong X-ray radiation inside a cavity (hohlraum), and the X-rays compress the pellet. In December 2022, the laser-driven fusion facility NIF reached ignition for the first time, producing about fifty percent more fusion energy than the laser energy delivered to the target.