poloidal

Poloidal is an adjective used in mathematics, physics, and engineering to describe features related to a poloid, an angular direction or loop that runs along the short, or minor, circumference of a torus. In toroidal coordinate systems, two angular coordinates describe motion around a torus: a poloidal angle that runs around the cross-section, and a toroidal angle that runs around the central hole of the torus.

In plasma physics and fusion research, the magnetic field in toroidal devices is often described in terms of toroidal and poloidal components. The poloidal component produces field lines that wrap around the minor circumference, while the toroidal component encircles the major circumference. The combination of both components yields helically wound field lines that improve magnetic confinement of the plasma.

In mathematical physics and geophysics, poloidal–toroidal decomposition is a way to express a divergence-free vector field as a sum of poloidal and toroidal parts. The poloidal part has field lines that lie in meridional planes containing the symmetry axis, while the toroidal part has field lines circulating around that axis. This decomposition is used to model phenomena such as the Earth's magnetic field and certain fluid flows.

The term poloidal is occasionally used to describe structures or directions that reflect this toroidal geometry in other contexts, and contrasts with toroidal, which refers to motion or features around the torus’s central axis.