Fast ions in a tokamak device exhibit a notable acceleration phenomenon during edge localized modes (ELMs). Presented here is an analytical analysis of the phase space transport of fast ions induced by ELMs. Counter to previous simulations, it is shown that ELMs can be inefficient in accelerating fast ions in the case of a low frequency nature. Instead, the transport of fast ions is characterized by the radial particle transport, as a result of the exchange of canonical toroidal angular momentum. The associated diffusivity is found to increase drastically for high energy particles, causing the velocity space measurements of fast ion losses to appear as an acceleration process. The theoretical results are not only consistent with recent experimental observations, but also carry practical implications for the performance of future tokamak reactors.
This paper analyzes how edge localized modes (ELMs) in tokamak devices can affect the transport of high-energy particles (fast ions). Contrary to previous beliefs, the study shows that ELMs may not efficiently accelerate fast ions, but instead, the transport is dominated by radial particle diffusion due to changes in the particles' angular momentum. This has important implications for the performance of future fusion reactors.