FAST-ION CONFINEMENT DURING OFF-AXIS NBI IN LOW COLLISIONALITY DISCHARGES AT ASDEX UPGRADE AND TCV

FAST-ION CONFINEMENT DURING OFF-AXIS NBI IN LOW COLLISIONALITY DISCHARGES AT ASDEX UPGRADE AND TCV

FAST-ION CONFINEMENT DURING OFF-AXIS NBI IN LOW COLLISIONALITY DISCHARGES AT ASDEX UPGRADE AND TCV 150 150 UKAEA Opendata

The fast-ion transport has been investigated in low-collisionality discharges at ASDEX Upgrade and TCV using offaxis neutral beams. In both devices Alfven eigenmode activity was observed which does, however, not strongly affect the global fast-ion confinement. In contrast, charge exchange losses have been identified to have a strong effect. At TCV up to 25% of the injected off-axis neutral beam injection (NBI) heating power is lost by charge-exchange while about 13% of charge exchange losses are observed in ASDEX Upgrade. The impact of charge exchange losses is weaker in ASDEX Upgrade, explained by higher fast-ion energies and a larger minor radius. In ASDEX Upgrade, however, a strong effect of resonant magnetic perturbations (RMPs) on the fast-ion confinement is observed in case of kink-like amplification of the RMP fields. Here, up to 20% of the fast ions are lost which agrees which modelling results.

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27th IAEA Fusion Energy Conference, Ahmedabad, India, 22-27 October 2018