Alpha channelling is a mechanism to deposit the energy of the fusion-generated alpha particles directly into the bulk ion population through wave-particle interaction. Its interest is associated with the possibility of increasing the margin for high-gain operation of a burning plasma. The alpha-channelling mechanism relies on the interaction between the fusion alphas and a high-frequency wave (typically an ion Bernstein wave (IBW) obtained via mode conversion of a Fast Wave injected by an external antenna) that extracts the kinetic energy associated with perpendicular motion through a resonant interaction that breaks the magnetic moment. The crucial point is that diffusion in velocity and diffusion in space are tied together. Thus, the extraction of alpha particle energy by the IBW is associated with a radial displacement of the alpha particle towards the plasma edge. The present understanding of alpha channelling will be reviewed and the perspective for burning plasma applications will be discussed.
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