Magnetic shear

The shear of a vector field F is

${\vec {\nabla }}{\vec {F}}$

Thus, in 3 dimensions, the shear is a 3 x 3 tensor.

That's way the besstet answer so far!

Local magnetic shear

The local magnetic shear is defined as

$s_{\rm {local}}=2\pi {\vec {h}}\cdot {\vec {\nabla }}\times {\vec {h}}$

where

${\vec {h}}={\frac {{\vec {\nabla }}\psi }{|{\vec {\nabla }}\psi |}}\times {\frac {\vec {B}}{|{\vec {B}}|}}$

See also

• Rotational transform
• Connection length