The application of neutral particle beams and/or high-frequency microwave radiation to the plasma from external sources, in order to provide the input heating power necessary to reach the temperatures required for fusion. Additional heating bridges the gap between resistive (or ohmic) heating due to plasma toroidal current (which gets weaker with increased temperature) and alpha-particle heating due to the slowing down of the helium reaction product in the plasma (which gets stronger with higher temperature).
A tokamak experiment run by the Massachusetts Institute of Technology (MIT) in Boston, USA up to the end of funding in 2016. One ot the three major US tokamaks (along with DIII-D and NSTX). See MIT's Plasma Science and Fusion Center.
The fusion between the nuclei of the hydrogen isotopes deuterium (D) and tritium (T) produces one helium nucleus, also called an "alpha particle," and one neutron.
The helium nucleus, which carries 20% of the energy produced by the fusion reaction, is electrically charged and remains confined by the magnetic fields of the tokamak. The heating provided by these alpha particles contributes to maintaining the temperature of the plasma. When heating by the helium nuclei is dominant ("alpha heating") the plasma is said to be a "burning plasma."
A thick wall of concrete surrounding the cryostat and designed to absorb the bulk of the remaining neutron radiation from the plasma. The wall shields the region outside the cryostat so that it can be accessed, at maximum a couple of weeks after shutdown, for major hands-on repairs.
The blanket covers the interior surfaces of the vacuum vessel, providing shielding to the vessel and the superconducting magnets from the heat and neutron fluxes of the fusion reaction. The neutrons are slowed down in the blanket, where their kinetic energy is transformed into heat energy and collected by the coolants. In a fusion power plant, this energy will be used for electrical power production. In ITER, some of the 440 individual blanket modules will be used to test materials for tritium breeding concepts.
In ITER, the blanket is subdivided in modules to allow it to be relatively easily replaced through equatorial access ports. There are 440 individual segments, each measuring 1x1.5 metres and weighing approximately 4.5 tons. Each segment has a detachable first wall which directly faces the plasma and removes the plasma heat load, and a semi-permanent blanket shield dedicated to neutron shielding.
If blanket modules contain lithium, a reaction occurs: the incoming neutron is absorbed by the lithium atom, which recombines into an atom of tritium and an atom of helium. The tritium can be removed from the blanket and recycled into the plasma as fuel. Blankets containing lithium are thus considered to be "breeding blankets" for tritium. Within the fusion reaction, tritium can be 'bred' indefinitely.
This will be important technology for future fusion power reactors.
A number of different combinations of tritium breeding material, neutron multiplier, structural material, and coolant will be tried out on ITER to determine the best combination for tritium and power production. Each one of these solutions is referred to as a "breeding technology". A future fusion plant producing large amounts of power will be required to breed all of its own tritium; ITER will test this essential concept of tritium self-sustainment.
A "Broader Approach" agreement for complementary research and development was signed in February 2007 between the European Atomic Energy Community (known by its initials EURATOM) and the Japanese government. It established a framework for Japan to conduct research and development in support of ITER and the next-stage device, DEMO, over a period of ten years.
A plasma in which the energy of the helium nuclei (alpha particles) produced by the fusion reaction is enough to maintain the temperature of the plasma; the external heating methods can then be strongly reduced or switched off altogether. A burning plasma in which at least 50 percent of the energy to drive the fusion reaction is generated internally is an essential step to reaching the goal of fusion power generation. At Q = 10 (ITER), approximately 66% of the plasma heating is contributed by the alpha particles.
The time the plasma is maintained at a temperature above the critical ignition temperature. To yield more energy from fusion than has been invested to heat the plasma, the plasma must be held up to this temperature for some minimum length of time, calculated from scaling laws.
The cooling water system provides for the rejection of heat from a variety of ITER systems and consists of the tokamak cooling water system, the component cooling water system, the chilled water system, and the heat rejection system.
The process by which the facility is permanently taken out of operation at the end of the plant lifecycle with adequate regard for the health and safety of workers and the public, and protection of the environment.
Demonstration fusion reactor. The next experimental device to follow ITER, and predecessor to a commercial-sized fusion reactor. DEMO would generate electricity at the level of a few hundred MW and utilize all technologies necessary for a commercial device.
A disruption is an instability that may develop within the tokamak plasma. Disruptions lead to the degradation or loss of the magnetic confinement of the plasma and, because of the high amount of energy contained within the plasma, the loss of confinement during a disruption can cause a significant thermal loading of in-vessel components together with high mechanical strains on the in-vessel components, the vacuum vessel and the magnet coils.
The component of the ITER device that removes helium "ash" and plasma heat during operation of the tokamak. Located at the very bottom of the vacuum vessel, the ITER divertor is made up of 54 remotely-removable cassettes, each holding three plasma-facing components, or targets. These are the inner and the outer vertical targets, and the dome.
Agencies created in each of the seven ITER Members to fulfil in-kind procurement responsibilities to ITER. In-kind procurement means that instead of supplying only cash to the ITER Organization for the construction phase of the project, Members are supplying 90% of their participation "in kind," in the form of systems, components and, in the case of Europe, buildings.
The building block of ITER's toroidal field and poloidal field superconducting magnets. Double pancakes are double layers of spiralled superconductor wound into the precise shape of the coil (D-shape for the toroidal field magnets, ring-shape for the poloidal field magnets). Six to nine double pancakes are stacked to form the final magnet assemblies.
The Experimental Advanced Superconducting Tokamak (EAST) is an experimental superconducting tokamak magnetic fusion energy reactor in Hefei, the capital city of Anhui Province, in eastern China. See this link.
Edge Localized Mode. Regular, energetic bursts of energy and particles that escape from the magnetic field surrounding the plasma and cause loss of energy. The mitigation of this phenomenon is an important preoccupation of tokamak physicists.
The first operational event in the ITER calendar, marking the end of the construction phase and the transition to operation. The nominal parameters for First Plasma in December 2025 have been established as a hydrogen plasma of at least 100 kA of plasma current for at least 100 milliseconds.
Small slugs of frozen deuterium and tritium fuel in the 3-6 mm diameter range fired frequently (up to 20 pellets per second) into the plasma to maintain sufficient fuel density in the plasma core. Pellet injection is also efficient in controlling Edge Localized Modes, or ELMs. Special technology is being developed to allow these pellets to fly along curved trajectories, thereby attaining specific zones within the plasmas where ELMs are particularly disruptive.
The "triple product" of density, confinement time and plasma temperature is used by researchers to measure the performance of a fusion plasma. The triple product has seen an increase of a factor of 10,000 in the last thirty years of fusion experimentation; another factor of six is needed to arrive at the level of performance required for a power plant.
Ash is the name given to the helium nuclei produced by fusion reactions in a deuterium-tritium plasma. Once the helium nuclei have shared their energy with the rest of the plasma they have no further use; their removal and replacement by deuterium-tritium fuel is required to prevent dilution of the plasma.
The H-mode is the baseline mode of plasma operation on all of today's major tokamaks. As the plasma auxiliary heating exceeds a certain threshold power the energy confinement of the plasma spontaneously doubles. This phenomenon was first discovered on ASDEX in 1982.
A concrete-shielded chamber with a controlled atmosphere that can be used to work on radioactive materials and components with a view to repairing them and refurbishing them for future re-use, or dismantling them for disposal. The chamber is equipped with remote manipulators or robotic devices for this purpose. No human access is foreseen.
International Fusion Materials Irradiation Facility, Naka, Japan. Part of the Broader Approach agreement, IFMIF is an international scientific research program designed to test materials for suitability for use in a fusion reactor. Jointly developed by Europe and Japan, IFMIF will use a particle accelerator-based neutron source to produce a large neutron flux, in a suitable quantity and time period to test the long-term behavior of materials under conditions similar to those expected at the inner wall of a fusion reactor. Engineering validation and engineering design activities (EVEDA) are currently underway. See more at IFMIF/EVEDA.
The point at which a fusion reaction becomes completely self-sustaining. At ignition, fusion self-heating is sufficient to compensate for all energy losses, external sources of heating power are no longer necessary to sustain the reaction.
The acronym ITER (pronounced "eater") is the Latin word for "the way." In choosing this name, the participants in the early Conceptual Design Activities for ITER (1988-1992) were expressing their common hopes that the project would lead to international cooperation on the development of a new form of energy. (The acronym also originally stood for International Thermonuclear Experimental Reactor—a name that is no longer used.)
International Tokamak Physics Activity. ITPA aims at cooperation in development of the physics basis for burning tokamak plasma physics, covering designs and issues broader than those represented by ITER. See the ITPA page hosted on the ITER website.
The cost estimates for the construction and operation phases of the ITER Project have been quantified using an internal currency called the "ITER Unit of Account" or IUA, established in 1989. The basis of conversion from IUA to Euro has been agreed between the Members and is updated each year.
Because seven ITER Members are collaborating to build ITER, each with responsibility for the procurement of in-kind hardware in its own territory with its own currency, the IUA was devised to measure the value of in-kind contributions consistently over time, and to neutralize market fluctuations.
The Joint European Torus, JET, is funded by the members of the EUROfusion Consortium and the European Commission and operated by the Culham Centre for Fusion Energy (CCFE, UK). The main part of its scientific program is dedicated to preparing for ITER operation.
In 1955, British physicist John Lawson (1923-2008) demonstrated that the conditions for fusion rely on three vital parameters: temperature (T), density (n) and confinement time (τ). [Lawson's Criteria]
Present in minerals and salt in the Earth's crust, lithium is the lightest metal. ITER will test specific lithium-containing wall modules to "breed" tritium. In effect, tritium can be produced within the tokamak when neutrons escaping the plasma interact with lithium contained in the blanket.
ITER will be the first fusion device to produce net energy. This means that the total power produced during a fusion plasma pulse will surpass the thermal power injected to heat the plasma. See Energy Breakeven.
High-energy beams of neutral atoms, typically a hydrogen isotope such as deuterium, that are injected into the core of the plasma through neutral beam injection. These energetic atoms transfer their energy to the plasma, raising the overall temperature.
The heating effect resulting from the resistance a medium offers to the flow of electric current. In a plasma subjected to ohmic heating, ions are heated almost entirely by the transfer of energy from the hotter electrons. Also known as resistive heating.
The fourth state of matter. At extreme temperatures, electrons are separated from nuclei and a gas becomes a plasma - a hot, electrically charged gas. In a star as in a fusion device, plasmas provide the environment in which light elements can fuse and yield energy. Some 99% of the known universe is in the plasma state. Examples of plasmas include the sun, fluorescent light bulbs, and other gas-discharge tubes.
Procurement Arrangements are a unique ITER invention. Each one of these documents governs the procurement of plant systems, components, or site construction and details all the necessary technical specifications and management requirements. The value of each Procurement Arrangement is expressed in ITER Units of Account (IUAs). About 140 individual Procurement Arrangements are currently planned to implement the work packages for building ITER.
(Fusion Gain): The ratio between the power produced by the fusion reactions and the external power required to sustain them via plasma heating. In ITER, the programmatic goal, Q≥10, signifies delivering ten times more power than that which is consumed by the heating systems. Breakeven corresponds to Q=1; ignition corresponds to Q=infinity. A burning plasma has a Q value of >1.
A quench is an abnormal termination of magnet operation that occurs when part of the superconducting coil loses its superconductive state, and reenters the normal, resistive state. Resistance results in ohmic heating in a specific area; this heat then rapidly causes other areas of the magnet to quench. ITER will be equipped with quench detection systems, and rapid discharge units to dissipate the excess magnet energy during a quench.
In ITER, the operation of the plasma in a way in which termination of the pulse is not determined by plasma behaviour, but is rather a choice of the operator. Operation that, in principle, can continue indefinitely.
A device invented by Lyman Spitzer (USA) for the containment of a plasma inside a racetrack-shaped tube. The toroidal device produces a poloidal field in a plasma with the use of external magnetic field coils.
Helium will remain liquid in a bath at 1 atmosphere pressure provided the temperature does not rise above 4.2K. If the ITER coils are placed in such a coolant bath and a high pulse of heat ensues in their operation, most of the helium must be vented to avoid large overpressures. To avoid this, the coils of ITER operate with pumped supercritical helium, just above the critical temperature, which retains a large measure of the heat transfer properties of liquid helium without the risk of overpressure.
A fusion device for containing a plasma inside a torus chamber through the use of two magnetic fields--one created by electric coils around the torus, the other created by intense electric current in the plasma itself. The tokamak was invented in the 1950s by Soviet physicists Igor Yevgenyevich Tamm and Andrei Sakharov. The term tokamak is a transliteration of a Russian expression (toroidalnaya kamera + magnitnaya katushka) meaning toroidal chamber with magnetic coils.
A superconducting fusion experiment at the Institute for Magnetic Fusion Research, IRFM (CEA Cadarache research centre) in France, which aims particularly at demonstrating long-pulse tokamak operation. Currently, Tore Supra is being upgraded with an actively cooled tungsten divertor (the WEST project) to serve as a test bed for ITER.
The basic means of driving toroidal current in the tokamak plasma uses the fact that most field lines created by the central solenoid pass down its bore and do not return on themselves until they pass outboard of (i.e., radially beyond) the plasma. This "inductive linkage" between the solenoid and plasma allows a change in current in the solenoid to drive current in the plasma (Maxwell's Laws).
Components of a tokamak that assist in stabilizing the plasma, by creating a "magnetic bottle" for confinement. In ITER, the toroidal field coil system consists of 18 D-shaped vertical coils placed around the vacuum vessel.
A surface of revolution generated by revolving a circle in three-dimensional space about an axis coplanar with and not touching the circle. Examples of tori include the surfaces of doughnuts and inner tubes. The solid contained by the surface is known as a toroid.