neoclassical transport is the irreducible level of collisional heat and particle loss in a toroidally confined 📝plasma — the transport floor set by the geometry of the magnetic field rather than by turbulence.
The name marks a revision. Classical transport theory describes how collisions let particles diffuse across a straight, uniform magnetic field, one 📝gyroradius-scale step at a time. Bending that field into a torus changes the answer: a 📝Tokamak's field is weaker on the outboard side, so a fraction of particles are trapped there on wide 📝banana orbits, and a single collision can displace a trapped particle across the full banana width rather than a single gyroradius. Neoclassical theory, developed through the 1960s and 1970s, is classical collisional theory corrected for this toroidal geometry, and it predicts losses that can exceed the classical estimate by more than an order of magnitude.
The theory earns its keep in two ways. It sets the floor no quieting of turbulence can beat — in practice, measured losses, especially of electron heat, usually sit well above it, the excess known as 📝anomalous transport — and it predicts genuinely new effects, most notably the 📝bootstrap current, a pressure-driven current the plasma generates on its own.