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Rotational transform: Difference between revisions
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:<math>q \simeq \frac{r B_\varphi}{R B_\theta}</math> | :<math>q \simeq \frac{r B_\varphi}{R B_\theta}</math> | ||
Where the poloidal magnetic field <math>{B_\theta}</math> is mostly produced by a toroidal plasma current. The principal significance of the safety factor q is that if <math>q \leq 2</math> at the last closed flux surface (the edge), the plasma is [[magnetohydrodynamically]] unstable.<ref>Wesson J 1997 Tokamaks 2nd edn (Oxford: Oxford University Press) p280 </ref> | Where the poloidal magnetic field <math>{B_\theta}</math> is mostly produced by a toroidal plasma current. The principal significance of the safety factor ''q'' is that if <math>q \leq 2</math> at the last closed flux surface (the edge), the plasma is [[:Wikipedia:Magnetohydrodynamics|magnetohydrodynamically]] unstable.<ref>Wesson J 1997 Tokamaks 2nd edn (Oxford: Oxford University Press) p280 ISBN 0198509227</ref> | ||
In [[Tokamak|tokamaks]] with a [[divertor]], q approaches infinity at the [[separatrix]], so it is more useful to consider q just inside the separatrix. Is is customary to use q at the 95% flux surface ( | In [[Tokamak|tokamaks]] with a [[divertor]], ''q'' approaches infinity at the [[separatrix]], so it is more useful to consider ''q'' just inside the separatrix. Is is customary to use ''q'' at the 95% flux surface (''q<sub>95</sub>''). | ||
== See also == | == See also == | ||