Neoclassical Transport

Neoclassical transport is the irreducible collisional leakage from a torus's geometry — and the source of the useful bootstrap current.

What

Collisional transport in toroidal geometry

Floor

The minimum leakage below turbulence

Bonus

Drives the self-generated bootstrap current

Contrast

Usually smaller than turbulent transport

Neoclassical transport is the collisional heat and particle leakage that arises purely from a tokamak's toroidal geometry — specifically from particles trapped in banana orbits on the weak-field side. It sets a floor on transport that exists even if all turbulence were switched off, though in practice turbulent transport is usually larger.

Neoclassical physics is not all loss, though: the same trapped-particle dynamics generate the bootstrap current, the self-driven plasma current that a high-performance tokamak like Kronos MetroVolt relies on to cut its external current-drive power. Understanding neoclassical transport is therefore essential to both the confinement and the current budgets.