Magnetic shear: Difference between revisions

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 surface|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

In tokamak research, the quantity ''q = 2π/ι'' is preferred (called the "safety factor").

:<math>s = \frac{r}{q} \frac{dq}{dr} = -\frac{r}{\iota} \frac{d\iota}{dr}</math>

<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/8/4375/1 M. Nadeem et al, ''Local magnetic shear and drift waves in stellarators'', Phys. Plasmas '''8''' (2001) 4375]</ref>