Term Definition
D-alpha light (D-alpha), radiation as decaying from the n=3 --> n=2 transition in deuterium atoms (near 6500 Å).
D-shaped plasma A toroidal plasma whose cross-section is in the form of a “D”.
DC direct current
DD reactions Reactions between nuclei of deuterium, to release energy by nuclear fusion, and in which helium nuclei and neutrons, or tritium and protons, are produced with roughly equal probability.
decay heat The heat produced from the radioactive decay of fission or neutron activation products.
decay time The time taken for the activity of a material to decay to the point at which the material can again be treated as if it is not activated.
decommissioning 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.
decontamination The removal or reduction of radioactive contamination by a physical and / or chemical process.
DEMO Demonstration fusion reactor. The next experimental device to follow ITER, and predecessor of a prototypical commercial-sized fusion reactor. DEMO would generate electricity at the level of a few hundred MW and utilise all technologies necessary for a commercial device. It does not have to produce electricity economically, but it does have to demonstrate convincingly that with some scaleup it could be economical. Reliable operation, after a shakedown period, is essential.
design value A numerical value for which the plant or a component is designed. Incorporates all margins (e.g. design margins, safety factors, tolerances) which might be required to cope with uncertainties.
deuterium An isotope of hydrogen with one neutron and one proton in the nucleus.
deuterium-tritium plasma (D-T plasma), a plasma consisting of a mixture of deuterium and tritium.
deviation A departure from normal operating states. A departure from the design during manufacturing.
diagnostics Equipment for determining (diagnosing) the properties and behaviour of a plasma during an experiment.
discharge (or release)
The release of radioactive or toxic substances (effluents) to the environment.
dispersion strengthened
(DS), a material which has enhanced strength by means of small granules of another material uniformly dispersed within it.
disruption A gross instability which gives rise to an abrupt temperature drop and the termination of the plasma. See "plasma disruption".
divertor The system for power and particle exhaust in a tokamak in which the plasma at the edge is "diverted" to a region remote from the main plasma by suitably modifying the magnetic field at the plasma edge.
divertor channel The region of the divertor into which field lines in the plasma scrape-off layer are conducted.
divertor configuration The arrangement and material composition of of plasma facing components and pumping slots on the divertor cassette.
divertor physics Plasma physics associated with toroidally confined plasmas with a null point in the confinement region designed to remove impurities from the interior of the plasma column.
double-null A tokamak plasma with two null points . See also "divertor physics".
double-null equilibrium A tokamak plasma configuration in which the field lines in the scrape-off layer intersect the plasma chamber walls or divertor at the top and bottom of the chamber. The poloidal field therefore has a field null at the top and bottom of the plasma core, and both nulls are within the plasma chamber. A single null configuration has only one null within the plasma chamber.
down-time The time for which the device cannot be operated, for various reasons.
driven current Current produced in a plasma to extend or maintain the pulse length of the inductive material.
DT reactions Reactions between the nuclei of two isotopes of hydrogen, deuterium and tritium, to release energy by nuclear fusion, and in which helium nuclei and neutrons are produced.
dump resistors Large current-carrying resistors which dissipate large amounts of electrical energy over a short period of time by ohmic heating.
duty factor The ratio of working time to total time for an intermittently operating device.
dwell time The time in each operational pulse which is not burn time.

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  Updated 13 February, 2017