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Magnetic shear: Difference between revisions
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Thus, in 3 dimensions, the shear is a 3 x 3 tensor. | Thus, in 3 dimensions, the shear is a 3 x 3 tensor. | ||
In the context of magnetic confinement, and assuming the existence of toroidally nested magnetic flux surfaces, the only relevant variation of the direction of the magnetic field is the radial gradient of the rotational transform (pitch). The latter is defined as | In the context of magnetic confinement, and assuming the existence of toroidally nested magnetic flux surfaces, the only relevant variation of the direction of the magnetic field is the radial gradient of the rotational transform (field line pitch). The latter is defined as | ||
:<math>\frac{\iota}{2 \pi} = \frac{d \psi}{d \phi}</math> | :<math>\frac{\iota}{2 \pi} = \frac{d \psi}{d \phi}</math> | ||
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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 | 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>[http://link.aip.org/link/?PHPAEN/3/2221/1 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'', Phys. Plasmas '''3''', 2221 (1996)]</ref> | <ref>[http://link.aip.org/link/?PHPAEN/3/2221/1 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'', Phys. Plasmas '''3''', 2221 (1996)]</ref> | ||
== References == | == References == | ||
<references /> | <references /> | ||