(Science: radiobiology) in a toroidal magnetic geometry, the fast spiraling of a charged particle around a magnetic field line is accompanied by a slow movement (drift) of the centre of the sprial. Particles with relatively low parallel energy are mirrored on the inside of the torus because the toroidal magnetic field has a 1/R dependence and is highest on the inside.
The combination of mirroring and drift produces a special class of particle orbits. Projected onto a poloidal plane, the drift orbit has the shape of a banana. These orbits are responsible for neo-classical diffusion and bootstrap current.