Experimental constraints on transport from dimensionless parameter scaling studies

Abstract

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 Xeff∝ q2.36±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, Tth∝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, τth ∝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. © 1998 American Institute of Physics.