Experimental constraints on transport from dimensionless parameter scaling studies

The scalings of heat transport with safety factor (q), normalized collisionality (ν), plasma beta (β), and relative gyroradius (ρ*) have been measured on the DIII-D tokamak [Fusion Technol. 8, 441 (1985)]. The measured ρ*, β and ν scalings of heat transport indicate that E x B transport from drift wave turbulence is a plausible basis for anomalous transport. For high confinement (H) mode plasmas where the safety factor was varied at fixed magnetic shear, the effective (or one-fluid) thermal diffusivity was found to scale like X_eff∝ q^2.36±0.64, with the ion and electron fluids having the same q scaling to within the experimental errors except near the plasma edge. The scaling of the thermal confinement time with safety factor was in good agreement with this local transport dependence, T_th∝q^-2.42±0.31 ; however, when the magnetic shear was allowed to vary to keep q₀ fixed during the (edge) safety factor scan, a weaker global dependence was observed, τ_th ∝q^-1.43±0.23₉₅. This weaker dependence was mainly due to the change in the local value of q between the two types of scans. The combined ρ_*, β, ν and q scalings of heat transport for H-mode plasmas on DIII-D reproduce the empirical confinement scaling using physical (dimensional) parameters with the exception of weaker power degradation.