Phenomenology of energetic-ion loss from the DIII-D tokamak

Thin-foil Faraday collectors mounted near the midplane measure energetic-ion loss signals from the DIII-D tokamak. Modulation of the neutral beam sources shows that, under appropriate conditions, prompt losses from every beam line are observed. Prompt losses are usually larger when the plasma current or toroidal field is low. Enhanced losses occur during ion cyclotron heating. Instabilities that produce strong field perturbations at the edge also produce enhanced losses.