Magnetic Shear

How the field-line pitch changes across the plasma; it stabilises turbulence and modes.

Magnetic shear is the variation of field-line pitch (the safety factor) from the plasma core to edge. Sheared field lines tear apart small instabilities and turbulent eddies, so shear is a stabilising design knob.

Sheared field lines tear apart small instabilities and turbulent eddies, so magnetic shear is a stabilising design knob. Its distribution, set by the current profile, decides where modes can grow and enables advanced regimes like reversed-shear operation with internal transport barriers.