| 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”. |
| DBA | design-basis accident, an accident which is used as the basis of establishing possible consequent sequences of events, and for which elements are introduced in the design to mitigate the effects. |
| DC | direct current |
| DD | Deputy Director(s) |
| 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. |
| DDD | Design Description Document, a detailed description of part of the ITER design. |
| 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 PROTO, a prototypical commenrcial-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 basis accidents | Accident conditions against which the reactor facility is designed according to established design criteria. |
| 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. |
| DIII-D | Doublet Version III - D-sphaped plasma variant. A fusion experiment run by General Atomic Inc in San Diego, California |
| direct cost | Any cost that can be specifically identified with a particular project or activity, including salaries, travel, equipment, and supplies directly benefitting the project or activity. Overheads, profits, materials, supplies, subcontracts, etc. are not included. |
| discharge (or release) |
The release of radioactive or toxic substances (effluents) to the environment. |
| dismantling | The disassembly and removal of any structure, system or component in decommissioning. May be performed immediately after permanent retirement of a facility or may be deferred. |
| dispersion strengthened |
(DS), a material which has enhanced strength by means of small granules of another material uniformly dispersed within it. |
| disposal | The emplacement of waste in an approved, specified facility without the intention of retrieval. Also covers the approved direct discharge of effluents (e.g. liquid and gaseous wastes) into the environment with subsequent dispersion. |
| disruption | A gross instability which gives rise to an abrupt temperature drop and the termination of the plasma. See "plasma disruption". |
| divertor | 1) The concept for power and particle exhuast 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. 2) The component of the ITER device that removes helium "ash" and plasma heat. |
| 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. |
| Divertor Refurbishment Platform | DRP - a facility built in Brasimone, Italy, to test the feasibility of remotely refurbishing the components of a diverotr cassette. Part of the ITER Large Project L7. |
| Divertor Test Platform | DTP -a facility built in Brasimone, Italy, to test the feasibility of diverotr cassette replacement in ITER. Part of the ITER Large Project L7. |
| dose | Without a qualifier, refers to a "50 year committed effective dose". See also "chronic dose", "committed effective dose", "committed equivalent dose", "early dose", "defective dose", "equivalent dose", "mean absorbed dose", and "plume-passage dose". |
| 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 ITER 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. |
| DS | dispersion strengthened, a means by which a material can be made tougher by the distribution within the material of other alloys or trace elements. |
| DT burn | see “burn”. |
| DT commissioning | Commissioning ITER for tritium operation in which significant material activation will occur. This period involves the checking of shielding and adjustment if necessary. |
| DT operation | Operation of the ITER plasma with a roughly equal mixture of deuterieum (D) and tritium (T). The period of ITER operation in which these pulses are the predominant mode of working. |
| 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. |
| early dose | A 50-year committed effective dose from 1-week exposure, i.e., inhalation and cloudshine from a plume passage plus groundshine from 1-week exposure. The early dose is always numerically higher than the plume passage dose. Ingestion is not included. |
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