Term Definition
L-H threshold power During plasma heating, in order to overcome conduction losses, a certain amount of external heating must be applied to establish the H-mode internal transport barrier which places the plasma core in a mode of improved energy confinement. This heating power is referrred to as the L-H threshold power.
L-mode Low mode, 1) The normal behavior of a plasma undergoing ohmic heating; that is, as the plasma's temperature climbs higher, the confinement of the plasma deteriorates. 2) A confinement regime in a tokamak in which the confinement time is low, named after discovery of the H-mode (high mode) of operation.
Landau Damping Damping of a plasma oscillation wave which occurs in situations where the particles of the plasma are able to increase their average velocity at the expense of the wave, and thus to damp it out, even in cases where the dissipative effects of collisions are unimportant.
Langmuir probe A probe used for measuring the plasma temperature (named after I. Langmuir who first employed it and developed the theory for interpretation of the measurements).
laser An acronym for light amplification by stimulated emission of radiation. An optical device that amplifies and concentrates light waves, emitting them in a narrow, intense beam.
laser scattering device Formally known as a "Thomson scattering device"; a diagnostic device used to measure electron temperature in a plasma by directing laser light into the plasma. The laser's photons scatter off the electrons, spreading in a manner proportional to the electron temperature.
Lawson criterion The minimum physical conditions of plasma temperature (T), plasma density (n), and confinement time (t) needed for the production of net power in fusion. It is expressed as nt>f(T), where f(T) has a minimum value of around 2 X 1020 sec/m3 for the deuterium-tritium reaction.
LHe liquid helium
limiter (Nuc. Eng.). An aperture which defines the boundary of a plasma and protects the vacuum vessel from damage by contact with the hot plasma.
limiter system Mechanical structures used to define the plasma boundary.
lip seal A metallic flange or "lip" extending around the perimeter of a component which must be hermetically sealed to another component. Sealing of the "lips" is accomplished by welding, and unsealing by grinding or cutting the lip seal weld.
LN liquid nitrogen (cryogenic), low nitrogen (material)
long-lead time A date prior to the estimated physical construction start to ensure availability at the time needed so as to not delay the construction performance.
lost alpha detectors Detectors used for measuring unconfined alpha particles.
low field regions Regions of lower (magnetic) field suitable for siting conductor joints, for instance, as the forces experienced during the plasma cycle will be minimised there. These are usually regions furthest away from the bore of the coil.
low-Z material In tokamaks, any material with a low atomic number, such as beryllium, carbon, boron, etc.
LTM long term maintenance

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  Updated 13 February, 2017