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Greenwald limit: Difference between revisions
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:<math>n_G = \frac{I_p}{\pi a^2}</math> | :<math>n_G = \frac{I_p}{\pi a^2}</math> | ||
where ''n<sub>G</sub>'' is the 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. | 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). | 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. | 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 | 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 == | ||
<references /> | <references /> | ||