Lawrence Livermore National Laboratory



Ablator: Plastic outer layer of the fuel capsule.

Ablation: Laser ablation is a process in which the molecular bonds of a material are dissolved by a laser. During an ignition experiment, laser beams strike the inside walls of the hohlraum and generate x rays that ablate the outer plastic shell and cause the capsule to implode like a spherical rocket at velocities greater than 350 kilometers per second.

Alpha Particle: The nucleus of a helium atom, consisting of two protons and two neutrons. A deuterium-tritium fusion reaction, in which the nuclei of these two hydrogen isotopes fuse, produces an alpha particle and a free neutron.

Areal Density: The combined thickness and density of the imploding frozen fusion fuel shell. The areal density of the fuel and the temperature and shape of the implosion at peak compression are two critical experimental factors for achieving ignition. NIF ignition experiments have demonstrated a steady increase in the areal density

Astrophysics: The branch of physics that deals with the universe, including the physical properties (luminosity, density, temperature, and chemical composition) and the interactions of astronomical objects such as stars, galaxies, and the interstellar medium. It also includes studies of the nuclear reactions that power stars. NIF experiments are recreating many astrophysical phenomena in the laboratory for the first time.

Blowoff: The rocket-like expulsion of hot material from the surface of an ignition fuel capsule, which causes it to implode, or compress rapidly, just as the expulsion of hot gas from a jet engine propels an aircraft.

Breakeven: In fusion, scientific breakeven occurs when the fusion power is equal to the laser input power (see Ignition). Commercial breakeven is when sufficient fusion power can be converted into electric power to cover the costs of the fusion power plant at economically competitive rates (see Inertial Fusion Energy).

Bundle: An array of eight laser beams stacked four high and two across, the basic building block of the NIF main laser system. Six bundles make up a cluster.

Burn: See Thermonuclear Burn.

Calorimeter: A device for measuring the energy of a laser pulse by measuring the temperature rise of an absorber.

Cluster: A grouping of six bundles of NIF beamlines, or 48 beamlines. There are two clusters in each of NIF's two main laser bays.

Commissioning: Certification that a system meets required specifications (see Operational Qualification and Performance Qualification).

Depleted Uranium (DU): The byproduct of enriched uranium, mainly composed of uranium-238, with less than one-third as much U-235 and U-234. The external radiation dose from DU is about 60 percent that of natural uranium.

Diagnostics: Ultra-fast and sensitive detectors, oscilloscopes, interferometers, streak cameras, and other instruments surrounding the NIF target chamber that are designed to capture and record the details and nuances of every shot. NIF currently has about 60 optical, nuclear, and temperature diagnostics.

Direct-Drive Ignition: An approach to inertial confinement fusion in which laser light is directly focused on a fusion fuel capsule, uniformly illuminating the capsule from all directions and resulting in compression heating from the ablation of the target surface (see Ignition). Compare with Indirect-Drive Ignition.

Disposable Debris Shield (DDS): A thin, 1-millimeter-thick sheet of inexpensive borosilicate glass that protects the main debris shield from target debris.

D-T Fuel: A mixture of the hydrogen isotopes deuterium and tritium. When sufficiently heated and compressed in a fuel capsule, the nuclei of the atoms fuse, producing an alpha particle and a free neutron.

Deuterium: An isotope of hydrogen, with one neutron and one proton in the nucleus.

Electron: A subatomic particle with negative electric charge that lies outside the nucleus of an atom.

Energy: The capacity of a physical system to do work; the units of energy are joules.

Enrichment: See Uranium Enrichment.

Final Optics Assembly (FOA): An assembly that includes the target chamber vacuum window, final optics cell, diffractive optics plate, debris shield, and some laser diagnostics. The FOAs focus and smooth NIF's beams and convert their frequency from infrared to ultraviolet light (see Wavelength) for more efficient interaction with the target (see Integrated Optics Module).

Final Optics Damage Inspection System (FODI): A system used to monitor the condition of the final optics in NIF beamlines, a key capability in the operation of the facility.

Fissile Material: Material that is fissionable, or capable of sustaining a chain reaction of nuclear fission.

Fission: A nuclear reaction in which the nucleus of an atom splits into at least two other nuclei, releasing a relatively large amount of energy. Two or three neutrons are usually released during this type of transformation. Fission is usually restricted to heavier nuclei such as isotopes of uranium, plutonium, and thorium.

Frequency: The number of complete oscillations of an object in a given period of time (see Wavelength).

Fuel Capsule: A hollow spherical capsule about the size of a BB containing a frozen layer of deuterium-tritium fusion fuel. Fuel capsules typically have outer shells made of plastic.

Fluence: The amount of laser energy passing through a given area, typically expressed in joules per square centimeter (see Irradiance).

Fusion: A nuclear reaction in which nuclei combine to form more massive nuclei with the simultaneous release of enormous amounts of energy.

High-Energy-Density Physics: The field of physics concerned with the properties and interactions of materials with energy densities exceeding 1011 joules per cubic meter, or equivalently, pressures exceeding one megabar (one million Earth atmospheres). NIF has become the leading international center for advancing high-energy-density physics.

High-Level Waste: Material resulting from the reprocessing of spent nuclear fuel and other highly radioactive material that must be permanently isolated. One of the advantages of a fusion power plant (see LIFE) is the absence of high-level and long-level waste.

Hohlraum: German for "hollow space," a hohlraum is a hollow metal cylinder the size of a pencil eraser surrounding a fusion fuel capsule. The hohlraum converts energy from laser light into x-ray radiation that symmetrically compresses a fuel capsule (see Indirect-Drive Ignition).

Ignition: In laser fusion, ignition is defined as energy output equal to or greater than the amount of laser energy incident on the target assembly (for indirect drive, the target assembly consists of the hohlraum and fuel capsule; for direct drive, it consists of the capsule). As in an ordinary (chemical) fire, ignition is the point at which the temperature and confinement of heat in the fuel (plasma in the case of fusion) are such that energy released from ongoing reactions is sufficient to maintain the temperature of the system and no external heating is needed. An ignited fusion plasma produces so much energy from fusion reactions that the plasma is fully heated by the fusion reaction products (alpha particles in the case of deuterium–tritium fusion).

Ignition Point Design: The set of specifications integrating all of the parameters—target design characteristics, diagnostics, and facility capabilities—required to build the components necessary to reach the goal of ignition.

Implode: Explode inward. The NIF fuel capsule implodes at speeds up to 400 kilometers a second.

Inertial Confinement Fusion: The approach to fusion in which a fuel capsule is imploded very quickly, so that the inertia of the converging fuel ions allows fusion to occur before the particles can disperse.

Indirect-Drive Ignition: An approach to inertial confinement fusion in which the inner surface of a hohlraum containing a fuel capsule is illuminated by laser beams entering through holes at its end caps. The laser energy is converted to x rays, which heat and ablate the capsule surface, causing a rocket-like pressure on the capsule and forcing it to implode (see Ignition). Compare with Direct-Drive Ignition.

Inertial Fusion Energy: In inertial fusion energy (IFE), beams of intense laser light are focused on a target filled with hydrogen fuel. An IFE power plant, such as conceived by the LIFE effort, would have separate areas for the driver, a factory for making the targets, a target chamber where the fusion reactions occur, and a steam turbine to generate electricity. The laser system would ignite several fusion targets per second to produce the desired power.

Integrated Optics Module (IOM): An assembly that holds and positions the target chamber vacuum window, final optics cell, diffractive optics plate, and debris shield for a single beam. The IOM is a line replaceable unit in the final optics assembly.

Ion: An atom or molecule that has acquired an electrical charge by the loss or gain of electrons.

Ionizing Radiation: Radiation, such as alpha, beta, gamma, and x rays, capable of displacing electrons from atoms or molecules, thereby producing ions. Exposure to high doses of ionizing radiation can produce severe skin or tissue damage and radiation sickness.

Irradiance: The amount of light energy incident on a given area of surface in a given amount of time, measured in Watts per square meter (see Fluence).

Isotope: Different forms of atoms of the same element. Isotopes have the same number of protons in their nuclei but a different number of neutrons (the same atomic number but different atomic weights). Uranium-238 and uranium-235 are isotopes of uranium. Isotopes may be stable (not spontaneously decaying) or unstable (spontaneously decaying, emitting ionizing radiation).

Joule: A unit of energy. One joule is the energy required to lift a small apple 1 meter against the Earth’s gravity. NIF has generated energy of more than 1.8 Megajoules (1.8 million joules) of ultraviolet light.

KDP Crystal: A potassium–dihydrogen–phosphate (KDP) crystal is a transparent material used in large laser systems such as NIF to change the frequency, or color, and the polarization of laser light. NIF laser light starts out as infrared but is converted to ultraviolet for better interaction with the target. NIF scientists helped to pioneer the technology of fast-growing KDP crystals.

Laser: An acronym for light amplification by stimulated emission of radiation. If the electrons in special atoms in glasses, crystals, or gases are energized into excited atomic states, they will emit light photons in response to a weak laser pulse. The photons will all be at the same wavelength and will also be “coherent,” meaning the light wave’s crests and troughs are all in lockstep. In contrast, ordinary visible light comes in multiple wavelengths and is not coherent.

Laser Fusion: A form of inertial confinement fusion in which laser beams are used to compress and heat a fuel capsule.

Laser Inertial Fusion Energy (LIFE) : An advanced fusion energy concept that builds on NIF technology to furnish safe, clean, and sustainable energy.

Light Water Reactor (LWR): A nuclear reactor that uses ordinary water as a neutron moderator, in contrast to heavy water reactors, which produce greater amounts of hazardous radioactive substances as by-products.

Line Replaceable Unit (LRU): A self-contained package containing multiple laser components that can be assembled and tested off-line in a cleanroom, then installed on the laser as a unit. NIF uses thousands of line replaceable units for lowered costs and higher efficiency.

Main Laser: The portion of the NIF beampath in which the laser light is generated, amplified, and transported to the target chamber (see Wavelength).

Magnetic Confinement Fusion: An approach to fusion energy in which magnetic fields confine a plasma that is heated until fusion occurs.

Master Oscillator: A device made from a ytterbium-doped optical fiber laser that generates the initial low-energy laser pulse of just a new nanojoules with a beam diameter of a few micrometers. The pulse is then broadened, split, and amplified many times before reaching the target chamber.

National Ignition Campaign: An effort sponsored by the National Nuclear Security Administration

that began in 2006 and ended September 30, 2012. It had three principal goals: achieving ignition and thermonuclear burn, developing a platform for ignition and high-energy-density applications (including target and diagnostic fabrication), and transitioning NIF to routine operations as the world’s preeminent high-energy-density user facility. The campaign involved the participation of Sandia National Laboratories, Los Alamos National Laboratory, General Atomics, and the Laboratory for Laser Energetics (LLE) at the University of Rochester. Other key contributors included the Massachusetts Institute of Technology, Lawrence Berkeley National Laboratory, Atomic Weapons Establishment in England and Commissariat a l’Energie Atomique in France.

National Nuclear Security Administration (NNSA): The NNSA, part of the U.S. Department of Energy, is responsible for the management and security of the nation’s nuclear weapons, nuclear nonproliferation, and naval reactor programs. The NNSA funds the National Ignition Facility.

Neutron – A subatomic particle with no charge that is located in the nucleus of an atom.

NIF Early Light: An experimental campaign in July 2003 in which NIF produced 10.4 kilojoules (kJ) of 350-nanometer (ultraviolet) laser light in a single beamline, setting a world record for laser performance and exceeding the NIF design requirements. World records for producing 11.4 kJ of green light and 26 kJ of infrared light were also achieved (see Wavelength).

Nuclear Fuel Cycle: The progression of nuclear fuel through a series of stages—preparation, service during reactor operation, and either containment and storage (open fuel cycle) or reprocessing for further use (closed fuel cycle).

Nuclear Reprocessing: See Reprocessing.

Nucleus: The positively charged dense core of an atom, containing protons and neutrons.

Omega: The last letter of the Greek alphabet, omega is the symbol used by physicists to denote frequency. The optics in NIF’s main laser produce laser light in the infrared portion of the electromagnetic spectrum, which is designated one-omega (1ω). NIF’s final optics double the light’s frequency to visible green light (2ω) and finally to ultraviolet light (3ω). Ultraviolet light is more effective than infrared at compressing NIF's fuel capsule (see Wavelength).

Operational Qualification (OQ): Certification of a system’s operational capability (see Performance Qualification).

Performance Qualification (PQ): Certification of a system’s ability of operate at full energy (see Operational Qualification).

Petawatt Laser: A laser capable of producing pulses with more than one quadrillion watts of peak power. A petawatt is 1015 watt.

Photon: A particle of light; a quantum (the smallest unit in which waves may be emitted or absorbed) of electromagnetic energy moving at the speed of light.

Plasma: Known as the “fourth state of matter,” a plasma is a substance in which many of the atoms or molecules are ionized, allowing charges to flow freely. Some 99% of the known universe is in the plasma state. Plasmas have unique physics compared to solids, liquids, and gases. Examples of plasmas include the sun, fluorescent light bulbs and other gas-discharge tubes, much of interplanetary, interstellar and intergalactic space, laser-produced plasmas, and plasmas produced for magnetic confinement fusion.

Power: The amount of work done per unit of time (see Energy). NIF has generated greater than 500 trillion watts of power.

Proliferation: The spread of nuclear weapons; the chance that fuel destined for a nuclear power plant could be diverted for weapons purposes.

Proton: A positively charged subatomic particle usually found in the nucleus of an atom.

Quad: A group of four NIF main laser beamlines. Two quads make up a bundle, and six bundles make up a cluster.

Radiation: Energy in the form of waves or particles sent out over a distance (see Ionizing Radiation).

Radioactivity: The emission of radiation, generally alpha particles or beta particles, often accompanied by gamma rays, from the nucleus of an unstable isotope. Also, the rate at which radioactive material emits radiation.

Stockpile Stewardship Program: A program run

by the National Nuclear Security Administration that maintains the reliability, security, and safety of the U.S. weapons stockpile without nuclear testing. NIF is a key element of stockpile stewardship.

Subcritical: Incapable of spontaneously starting or sustaining a nuclear chain reaction.

Target: For indirect drive experiments, the NIF target is the fuel capsule together with the encompassing hohlraum. For direct-drive experiments the target is the fuel capsule alone.

Target Chamber: A ten-meter-diameter spherical structure assembled from ten-centimeter-thick aluminum panels that were preformed and welded in place. The NIF target chamber is covered with 0.3 meters of concrete injected with boron to absorb neutrons. The entire structure weighs 264,000 pounds.

Thermonuclear Burn: In a fusion reaction, burn is achieved by heating the fuel to the point where nuclei have sufficient energy to fuse when they collide, typically requiring temperatures of at least 1 million kelvins (1.8 million degrees Fahrenheit). Thermonuclear fusion converts a small amount of the mass of the reactants into energy via E = mc² and is the process by which most types of stars, including the sun, produce the energy to shine.

Transmute:To change or alter in form, especially to a higher form. During fusion, deuterium and tritium, both isotopes of hydrogen, transmute to helium.

Tritium: An isotope of hydrogen that has two neutrons and one proton in the nucleus. Tritium is unstable, with a half-life of 12.32 years.

Uranium: The heaviest element normally found in nature. The principal fuel material used in today's nuclear reactors is the fissile isotope uranium-235.

Uranium Enrichment: A process by which the percent composition of uranium-235 is increased through isotope separation to make it an effective fuel in nuclear reactors. Naturally occurring uranium ore is 99% uranium-238. Enriched uranium is a critical component for both nuclear power generation and nuclear weapons.

Wavelength: The distance between adjacent crests or troughs of a light wave, which determines its color. The optics in NIF’s main laser produce infrared laser light with a wavelength of 1,053 nanometers (billionths of a meter), also known as one-omega (1ω). In NIF's final optical assembly, the infrared light is converted to visible green light (527 nm, or 2ω) and then to ultraviolet light (351 nm, or 3ω) as it's directed to the center of the target chamber (see Frequency).