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> | 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. | ||
In tokamaks (and RFPs), exceeding the Greenwald limit typically leads to a 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). | In tokamaks (and RFPs), exceeding the Greenwald limit typically leads to a 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). | ||
Revision as of 21:52, 6 September 2009
The Greenwald is a operational limit for the density in magnetic confinement devices: [1]
where nG is the density in 1020 m-3, Ip the plasma current in MA, and a the minor radius in m.
In tokamaks (and RFPs), exceeding the Greenwald limit typically leads to a 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 Ip by an equivalent current corresponding to the magnetic field).
The mechanism behind this phenomenological limit is not understood, but probably associated with edge gradient limits.