In
toroidally confined fusion plasma experiments the term zonal flow means a
plasma flow within a magnetic surface primarily in the
poloidal
The terms toroidal and poloidal refer to directions relative to a torus of reference. They describe a three-dimensional coordinate system in which the poloidal direction follows a small circular ring around the surface, while the toroidal direc ...
direction. This usage is inspired by the analogy between the quasi-two-dimensional nature of large-scale atmospheric and oceanic flows, where
zonal means latitudinal, and the similarly quasi-two-dimensional nature of low-frequency flows in a strongly magnetized plasma.
Zonal flows in the toroidal plasma context are further characterized by
* being localized in their
radial
Radial is a geometric term of location which may refer to:
Mathematics and Direction
* Vector (geometric), a line
* Radius, adjective form of
* Radial distance, a directional coordinate in a polar coordinate system
* Radial set
* A bearing f ...
extent transverse to the magnetic surfaces (in contrast to global plasma rotation),
* having little or no variation in either the
poloidal or toroidal direction—they are ''m'' = ''n'' = 0 modes (where ''m'' and ''n'' are the poloidal and toroidal mode numbers, respectively),
* having zero real frequency when analyzed by linearization around an unperturbed toroidal equilibrium state (in contrast to the geodesic acoustic mode branch, which has finite frequency).
* Arising via a
self-organization
Self-organization, also called spontaneous order in the social sciences, is a process where some form of overall order arises from local interactions between parts of an initially disordered system. The process can be spontaneous when suff ...
phenomenon driven by low-frequency drift-type modes, in which energy is transferred to longer wavelengths by modulational instability or
turbulent
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
inverse cascade.
See also
*
Zonal and poloidal In magnetic confinement fusion the zonal direction primarily connotes the poloidal direction (i.e. the short way around the torus), the corresponding coordinate being denoted by ''y'' in the slab approximation or ''θ'' in magnetic coordinates. How ...
*
Zonal flow
*
List of plasma (physics) articles
References
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Plasma physics
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