Physics Considerations on Plasma Transport

Aspects of the scaling of anomalous thermal diffusivities are discussed, particularly with respect to ρ_*, v_* and β. The ability of a number of transport models (drift wave, magnetic island and MHD) to lead to the experimentally observed scalings are discussed. Their capacity to explain a variety of improved confinement regimes (H, VH, high β_p and low magnetic shear) is also briefly considered.