National Ignition Facility

The National Ignition Facility (NIF), is a large laser-based inertial confinement fusion (ICF) research device, located at the Lawrence Livermore National Laboratory in Livermore, California. NIF uses lasers to heat and compress a small amount of hydrogen fuel with the goal of inducing nuclear fusion reactions. NIF's mission is to achieve fusion ignition with high energy gain, and to support nuclear weapon maintenance and design by studying the behavior of matter under the conditions found within nuclear weapons. NIF is the largest and most energetic ICF device built to date, and the largest laser in the world.Viewing port allows a look into the interior of the 30 foot diameter target chamber.Exterior view of the upper 1/3 of the target chamber. The large square beam ports are prominent.A technician loads an instrument canister into the vacuum-sealed diagnostic instrument manipulator.The flashlamps used to pump the main amplifiers are the largest ever in commercial production.The glass slabs used in the amplifiers are likewise much larger than those used in previous lasers. The National Ignition Facility (NIF), is a large laser-based inertial confinement fusion (ICF) research device, located at the Lawrence Livermore National Laboratory in Livermore, California. NIF uses lasers to heat and compress a small amount of hydrogen fuel with the goal of inducing nuclear fusion reactions. NIF's mission is to achieve fusion ignition with high energy gain, and to support nuclear weapon maintenance and design by studying the behavior of matter under the conditions found within nuclear weapons. NIF is the largest and most energetic ICF device built to date, and the largest laser in the world. The basic concept of all ICF devices is to rapidly collapse a small amount of fuel so the pressure and temperature reach fusion-relevant conditions. NIF does this by heating the outer layer of a small plastic sphere with the world's most powerful laser. The energy from the laser is so intense that it causes the plastic to explode, squeezing down on the fuel inside. The speed of this process is enormous, with the fuel reaching a peak around 350 km/s, raising the density from about that of water to about 100 times that of lead. The delivery of energy and the adiabatic process during collapse raises the temperature of the fuel to hundreds of millions of degrees. At these temperatures, fusion processes occur very rapidly, before the energy generated in the fuel causes it to explode outward as well. Construction on the NIF began in 1997 but management problems and technical delays slowed progress into the early 2000s. Progress after 2000 was smoother, but compared to initial estimates, NIF was completed five years behind schedule and was almost four times more expensive than originally budgeted. Construction was certified complete on 31 March 2009 by the U.S. Department of Energy, and a dedication ceremony took place on 29 May 2009. The first large-scale laser target experiments were performed in June 2009 and the first 'integrated ignition experiments' (which tested the laser's power) were declared completed in October 2010. Bringing the system to its full potential was a lengthy process that was carried out from 2009 to 2012. During this period a number of experiments were worked into the process 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 ​1⁄10 the conditions needed for ignition. Experiments since then have pushed this closer to ​1⁄3, but considerable theoretical and practical work is required if the system is ever to reach ignition. Since 2012, NIF has been used primarily for materials science and weapons research. Inertial confinement fusion (ICF) devices use drivers to rapidly heat the outer layers of a target in order to compress it. The target is a small spherical pellet containing a few milligrams of fusion fuel, typically a mix of deuterium (D) and tritium (T). The energy of the laser heats the surface of the pellet into a plasma, which explodes off the surface. The remaining portion of the target is driven inward, eventually compressing it into a small point of extremely high density. The rapid blowoff also creates a shock wave that travels toward the center of the compressed fuel from all sides. When it reaches the center of the fuel, a small volume is further heated and compressed to a greater degree. When the temperature and density of that small spot are raised high enough, fusion reactions occur and release energy. The fusion reactions release high-energy particles, some of which, primarily alpha particles, collide with the surrounding high density fuel and heat it further. If this process deposits enough energy in a given area it can cause that fuel to undergo fusion as well. However, the fuel is also losing heat through x-ray losses and hot electrons leaving the fuel area, so the rate of alpha heating must be greater than these losses, a condition known as bootstrapping. Given the right overall conditions of the compressed fuel—high enough density and temperature—this bootstrapping process will result in a chain reaction, burning outward from the center where the shock wave started the reaction. This is a condition known as ignition, which will lead to a significant portion of the fuel in the target undergoing fusion and releasing large amounts of energy. To date most ICF experiments have used lasers to heat the target. Calculations show that the energy must be delivered quickly in order to compress the core before it disassembles. The laser energy also must be focused extremely evenly across the target's outer surface in order to collapse the fuel into a symmetric core. Although other drivers have been suggested, notably heavy ions driven in particle accelerators, lasers are currently the only devices with the right combination of features. NIF aims to create a single 500 terawatt (TW) peak flash of light that reaches the target from numerous directions at the same time, within a few picoseconds. The design uses 192 beamlines in a parallel system of flashlamp-pumped, neodymium-doped phosphate glass lasers. To ensure that the output of the beamlines is uniform, the initial laser light is amplified from a single source in the Injection Laser System (ILS). This starts with a low-power flash of 1053-nanometer (nm) infra-red light generated in an ytterbium-doped optical fiber laser known as the Master Oscillator. The light from the Master Oscillator is split and directed into 48 Preamplifier Modules (PAMs). Each PAM contains a two-stage amplification process. The first stage is a regenerative amplifier in which the pulse circulates 30 to 60 times, increasing in energy from nanojoules to tens of millijoules. The light then passes four times through a circuit containing a neodymium glass amplifier similar to (but much smaller than) the ones used in the main beamlines, boosting the nanojoules of light created in the Master Oscillator to about 6 joules. According to Lawrence Livermore National Laboratory (LLNL), the design of the PAMs was one of the major challenges during construction. Improvements to the design since then have allowed them to surpass their initial design goals.