Transport studies in the TEXT Tokamak

Abstract

The TEXT tokamak (BT=3 T; R=1 m; a=.27 m) has been used for extensive studies of particle and electron thermal transport and of the microturbulence which may be causing the transport, which is observed to be far greater than neoclassical predictions. Transport may be determined as a function of minor radius except in the edge 5 cm; observations of turbulence span the entire cross-section. For impurity ion transport, a simple combination of diffusion and inward convection accurately describes the evolution of Sc+10 through Sc+18 following scandium injection by laser ablation. The coefficients show no strong dependence on plasma current or density. Applying these same coefficients to hydrogen implies equilibrium profiles and response to gas puffing consistent with those observed. Electron thermal transport is similar to that in other ohmic discharges. The associated microturbulence has been thoroughly characterized by FIR scattering throughout the plasma volume, supplemented by edge probe measurements. The density fluctuations can be generically described as strong drift-wave turbulence, propagating in the electron diamagnetic direction with an average phase velocity above vde, peaking at kperpendicular to rho s<1, and larger at the edge. The edge measurements confirm that the turbulence drives an outward radial particle flux.