4,377
edits
Magnetic shear: Difference between revisions
Updated reference links
(Updated reference links) |
|||
| (6 intermediate revisions by 4 users not shown) | |||
| Line 4: | Line 4: | ||
Thus, in 3 dimensions, the shear is a 3 x 3 tensor. | Thus, in 3 dimensions, the shear is a 3 x 3 tensor. | ||
== Global magnetic shear == | == Global magnetic shear == | ||
In the context of magnetic confinement, and assuming the existence of toroidally nested magnetic [[Flux surface|flux surfaces]], the only relevant variation of the direction of the magnetic field is the radial gradient of the [[Rotational transform|rotational transform]]. | |||
The global magnetic shear is defined as | The global magnetic shear is defined as | ||
| Line 24: | Line 14: | ||
High values of magnetic shear provide stability, since the radial extension of helically resonant modes is reduced. | High values of magnetic shear provide stability, since the radial extension of helically resonant modes is reduced. | ||
Negative shear also provides stability, possibly because convective cells, generated by curvature-driven instabilities, are sheared apart as the field lines twist around the torus. | Negative shear also provides stability, possibly because convective cells, generated by curvature-driven instabilities, are sheared apart as the field lines twist around the torus. | ||
<ref> | <ref>T.M. Antonsen, Jr., et al, ''Physical mechanism of enhanced stability from negative shear in tokamaks: Implications for edge transport and the L-H transition'', [[doi:10.1063/1.871928|Phys. Plasmas '''3''', 2221 (1996)]]</ref> | ||
== Local magnetic shear == | == Local magnetic shear == | ||
The local magnetic shear is defined as | The local magnetic shear is defined as | ||
<ref> | <ref>M. Nadeem et al, ''Local magnetic shear and drift waves in stellarators'', [[doi:10.1063/1.1396842|Phys. Plasmas '''8''' (2001) 4375]]</ref> | ||
:<math>s_{\rm local} = 2 \pi \vec{h} \cdot \vec{\nabla} \times \vec{h}</math> | :<math>s_{\rm local} = 2 \pi \vec{h} \cdot \vec{\nabla} \times \vec{h}</math> | ||
| Line 36: | Line 26: | ||
:<math>\vec{h} = \frac{\vec{\nabla} \psi}{|\vec{\nabla} \psi|} \times \frac{\vec{B}}{|\vec{B}|}</math> | :<math>\vec{h} = \frac{\vec{\nabla} \psi}{|\vec{\nabla} \psi|} \times \frac{\vec{B}}{|\vec{B}|}</math> | ||
== See also == | |||
* [[Rotational transform]] | |||
* [[Connection length]] | |||
== References == | == References == | ||
<references /> | <references /> | ||