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Term Definition
IGBT insulated gate bipolar transistor
ignition See “controlled ignition”.
IM initial magnetisation
impurities Atoms of unwanted elements in the plasma usually originating from the surrounding walls.
in-vessel components The in-vessel components comprise the blanket, the divertor, the fuelling and internal pumping systems, the port plugs, and diagnostic sensors mounted directly on the vessel.
inboard A region located further toward the tokamak vertical centreline than the object referred to.
inboard plasma shape The shape of the plasma inboard (i.e towards the machine centre) of the major circumference. This is strongly affected by the nearest poloidal field coils, usually the central solenoid.
inductively driven plasmas 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).
inherent safety characteristic Achieving safety by eliminating a specified hazard by means of the choice of material or design concept.
inspection Examination, observation or measurement to determine the conformance of materials, parts, components, systems, structures, as well as processes and procedures, with defined requirements.
instability A plasma state in which any small perturbation is amplified to a considerable change in the equilibrium of the system, leading to disruptions.
internal mode Magnetohydrodynamic instabilities which occur at the center of a tokamak plasma which cannot be controlled or suppressed by external means.
internal transport barrier ITB, a magnetic field configuration which slows down energy conduction transverse to it. In the establishment of the H-mode, an ITB is established just inside the separatrix, helping to hold heat inside the plasma. Other ITBs have been found also inside the plasma core, although the conditions for their creation and their usefullness is not yet fully understood.
ion An atom which has become charged as a result of gaining or losing one or more orbiting electrons. A completely ionized atom is one stripped of all its electrons.
ion-Berstein wave A plasma wave named after the discoverer, I.B. Bernstein.
ionization The removing or adding of an electron to a neutral atom, thereby creating an ion.
IR infra-red
ISO International Organization for Standardization
isotope One of several versions of the same element, possessing different numbers of neutrons but the same number of protons in their nuclei.
isotopic content The mix of given isotopes in a mixture of isotopes, for instance the amount of tritium and other hydrogenn isotopes in a waste gas stream.
isotopic mass The mass of each atom of a material in atomic mass units (see above). Thus the plasma isotopic mass for fusion is 2.5, since the fuel is basically a 50/50 mix of deuterium (2 amu) and tritium (3 amu).
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  Updated 13 February, 2017