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Greenwald limit: Difference between revisions
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The Greenwald limit is an operational limit for the density in magnetic confinement devices: | |||
<ref>M. Greenwald, ''Density limits in toroidal plasmas'', [[doi:10.1088/0741-3335/44/8/201|Plasma Phys. Control. Fusion '''44''' (2002) R27-R53]]</ref> | |||
:<math>n_G = \frac{I_p}{\pi a^2}</math> | |||
where ''n<sub>G</sub>'' is the line averaged density in 10<sup>20</sup> m<sup>-3</sup>, ''I<sub>p</sub>'' the plasma current in MA, and ''a'' the minor radius in m. | |||
In [[tokamak]]s (and [[Reversed Field Pinch]]es<ref>M.E. Puiatti, P. Scarin, G. Spizzo, et al., ''High density limit in reversed field pinches'', [[doi:10.1063/1.3063060|Phys. Plasmas '''16''' (2009) 012505]]</ref>), exceeding the Greenwald limit typically leads to a [[Disruption|disruption]], although sometimes the limit can be crossed without deleterious effects (especially with peaked density profiles). [[Stellarator]]s can typically exceed the Greenwald limit by factors of 2 to 5, or more (replacing ''I<sub>p</sub>'' by an equivalent current corresponding to the magnetic field). | |||
The mechanism behind this phenomenological limit is not fully understood, but probably associated with edge gradient limits. | |||
Recently, an explanation based on the formation of magnetic islands was proposed. <ref>D.A. Gates and L. Delgado-Aparicio, ''Origin of Tokamak Density Limit Scalings'', [[doi:10.1103/PhysRevLett.108.165004|Phys. Rev. Lett. '''108''' (2012) 165004]]</ref> | |||
== See also == | |||
[[Beta]] | |||
== References == | |||
<references /> | |||