The National Ignition Facility (NIF) is a laser-based inertial confinement fusion (ICF) research device, located at Lawrence Livermore National Laboratory in Livermore, California, United States. NIF's mission is to achieve fusion ignition with high energy gain. It achieved the first instance of scientific breakeven controlled fusion in an experiment on December 5, 2022, with an energy gain factor of 1.5. It supports nuclear weapon maintenance and design by studying the behavior of matter under the conditions found within nuclear explosions.
NIF is the largest and most powerful ICF device built to date. The basic ICF concept is to squeeze a small amount of fuel to reach pressure and temperature necessary for fusion. NIF hosts the world's most energetic laser. The laser heats the outer layer of a small sphere. The energy is so intense that it causes the sphere to implode, squeezing the fuel inside. The implosion reaches a peak speed of , raising the fuel density from about that of water to about 100 times that of lead. The delivery of energy and the adiabatic process during implosion raises the temperature of the fuel to hundreds of millions of degrees. At these temperatures, fusion processes occur in the tiny interval before the fuel explodes outward.
Construction on the NIF began in 1997. NIF was completed five years behind schedule and cost almost four times its original budget. Construction was certified complete on March 31, 2009, by the U.S. Department of Energy. The first large-scale experiments were performed in June 2009 and the first "integrated ignition experiments" (which tested the laser's power) were declared completed in October 2010.
From 2009 to 2012 experiments were conducted under the National Ignition Campaign, with the goal of reaching ignition just after the laser reached full power, some time in the second half of 2012. The campaign officially ended in September 2012, at about the conditions needed for ignition. Thereafter NIF has been used primarily for materials science and weapons research. In 2021, after improvements in fuel target design, NIF produced 70% of the energy of the laser, beating the record set in 1997 by the JET reactor at 67% and achieving a burning plasma. On December 5, 2022, after further technical improvements, NIF reached "ignition", or scientific breakeven, for the first time, achieving a 154% energy yield.
Inertial confinement fusion basics
Inertial confinement fusion (ICF) devices use intense energy to rapidly heat the outer layers of a target in order to compress it. In an H-bomb, this is provided by a nuclear fission explosive. In non-fission devices, energy sources include laser and particle beams.
The target is a small spherical pellet containing a few milligrams of fusion fuel, typically a mix of deuterium (D) and tritium (T), as this composition has the lowest ignition temperature.
Multiple laser beams heat the surface of the pellet into a plasma, which explodes away from the surface. The rest of the pellet is driven inward on all sides, into a small volume of extremely high density. The surface explosion creates shock waves that travel inward. At the center of the fuel, a small volume is further heated and compressed. When the temperature and density are high enough, fusion reactions occur. The energy must be delivered quickly and spread extremely evenly across the target's outer surface in order to compress the fuel symmetrically.
The reactions release high-energy particles, some of which, primarily alpha particles, collide with unfused fuel and heat it further, potentially triggering additional fusion. At the same time, the fuel is also losing heat through x-ray losses and hot electrons leaving the fuel area. Thus the rate of alpha heating must be greater than the loss rate, termed bootstrapping. Given the right conditions—high enough density, temperature, and duration—bootstrapping results in a chain reaction, burning outward from the center. This is known as ignition, which fuses a significant portion of the fuel and releases large amounts of energy.
As of 1998, most ICF experiments had used laser drivers. Other drivers have been examined, such as heavy ions driven by particle accelerators.