| Term | Definition |
|---|---|
| natural water convection | Warm water is less dense than cool water so temperature gradients in a body of water can cause it to circulate, particularly when heat sources are low down and heat sinks are high up. This is exploited in the ITER vessel cooling, in which the heat exchangers with the environment are placed on the roof of the ITER building so that if the vessel cooing pumps fail natural flow of water will be established between the hot tokamak and the cooler environment, allowing the tokamak to be cooled without any power. |
| NB | neutral beam |
| NbAl insert | CS model coil insert coil in which the relatively flexible superconductor is a compound of niobium and aluminium, suitable for use at fields above 12T with helium coolant at 4.5K. |
| NBCD | neutral beam current drive |
| NBI | neutral beam injection |
| NbTi | Flexible superconductor made of niobium titanium compound suitable for use up to 10T with helium coolant at 4.5 K. |
| negative ion sources | Sources of negative deuterium ions used in Neutral beam Injection |
| Negotiators | Individuals, appointed by the ITER participants to negotiate the terms of the Joint Implementation Agreement on ITER Construction, and to prepare for a decision on the site, cost sharing and senior staff appointments. |
| neoclassical tearing modes | NTMs, an MHD stability caused by the formation of magnetic islands (loops of magnetic flux) near integral or rational q (safety factor) surfaces. |
| neoclassical transport | (Nuc. Eng.) The departure from classical transport in a tokamak due to toroidal effects as predicted by theory. |
| neutral beam current drive | NBCD, noninductive current drive using high energy neutral beam injection. |
| Neutral Beam Injection | Neutral beam injectors on ITER use negative deuterium ions from an arc discharge between tungsten cathodes and the source body anode. These are accelerated into a gas neutraliser. Neutral particles continue on into the plasma while charged ions are deflected, collected and recycled. |
| neutral beams | A beam of high-energy atoms used to heat a plasma. As the atoms are neutral, the beam is not affected by magnetic fields. |
| neutral particle beam |
NPB, a concentrated, nearly unidirectional flow of neutral particles. |
| neutron fluence | The time integral of the neutron flux. |
| neutron flux | The number of neutrons passing through unit area in unit time, or the product of the number of neutrons per unit volume and their mean speed. |
| neutron wall loading | Energy flux carried by fusion neutrons into the first physical boundary that surrounds the plasma. |
| non-circular cross section | A plasma configuration which has a higher vertical height than horizontal width. |
| non-inductive current drive | Methods of driving a current in a tokamak other than with a transformer. |
| NSTX | National Spherical Tokamak Experiment, Princeton, USA. |
| nuclear regulators | Organisations which are responsible for licensing nuclear installations in potential ITER host countries. |
| null point | zero magnetic field |
| numerical codes | Computer codes ( to distinguish them from codes of practice, such as structural design codes). |
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