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| The Greenwald limit is an operational limit for the density in magnetic confinement devices:
| | HHIS I shulod have thought of that! |
| <ref>[http://dx.doi.org/10.1088/0741-3335/44/8/201 M. Greenwald, ''Density limits in toroidal plasmas'', Plasma Phys. Control. Fusion '''44''' (2002) R27-R53]</ref>
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| :<math>n_G = \frac{I_p}{\pi a^2}</math>
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| 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.
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| In tokamaks (and RFPs), 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). Stellarators 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).
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| The mechanism behind this phenomenological limit is not understood, but probably associated with edge gradient limits.
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| == References ==
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| <references />
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