Fast-ion transport studies using FIDA spectroscopy at the ASDEX Upgrade tokamak

The confinement of fast-ions generated by neutral beam injection (NBI) has been investigated experimentally in the ASDEX Upgrade tokamak using fast-ion D-alpha (FIDA) spectroscopy. This technique is based on the observation of Doppler shifted Balmer alpha radiation emitted by neutralized fast-ions. Newly installed lines of sight with horizontal and vertical viewing geometries provide information on different parts of the fast-ion phase space. Due to the good spatial and temporal resolution of the FIDA diagnostic, the effect of magnetic reconnection events linked to sawtooth crashes could be investigated. A radial redistribution of up to 50% of the central fast-ion population has been observed and predictions of the fast-ion redistribution based on the Kadomtsev model show good agreement with the measurement. In MHD-quiescent discharges, the fast-ion transport properties have been studied under different conditions, such as on- and off-axis NBI injection. The FIDA measurements have been compared to simulated fast-ion distribution functions and good agreement has been achieved under the assumption of neo-classical fast-ion diffusion. This indicates that, in the absence of significant MHD-activity, the anomalous fast-ion transport is small and below sensitivity of the diagnostic.