Neoclassical Transport

The irreducible, geometry-driven leakage of heat and particles across the field.

Even a perfectly stable plasma loses heat by collisional transport enhanced by the torus geometry — neoclassical transport. It sets a floor below which confinement cannot fall; real machines usually lose more, via turbulence.

The bootstrap current is itself a neoclassical effect, which is why good confinement and self-driven current tend to come together.