Analysis of the ion energy transport in ohmic discharges in the ASDEX tokamak

Abstract

An analysis of the local ion energy transport is performed for more than one hundred well documented ohmic ASDEX discharges. These are characterized by three different confinement regimes: the linear ohmic confinement (LOC), the saturated ohmic confinement (SOC) and the improved ohmic confinement (IOC). All three are covered by this study. To identify the most important local transport mechanism of the ion heat, the ion power balance equation is analysed. Two methods are used: straightforward calculations with experimental data only, and a comparison of measured and calculated profiles of the ion temperature and the ion heat conductivity, respectively. A discussion of the power balance shows that conductive losses dominate the ion energy transport in all ohmic discharges of ASDEX. Losses due to sawtooth activity play a role only inside the q = 1 surface, while at the edge convective fluxes and CX losses influence the ion energy transport. Both methods lead to the result that both the ion temperature and the ion heat conductivity are consistent with predictions of neoclassical theory. Enhanced heat losses as suggested by theories, e.g. on the basis of modes, can be excluded.