Resonance phenomena accompanying the injection of a periodically pulsed neutral beam into a tokamak

This paper considers the temporal behaviour of fast ions produced in a tokamak plasma by the injection of a periodically pulsed neutral beam. It is shown that, if the temporal distance between the pulses is properly chosen, then a dense bunch of fast ions is formed near a certain resonant magnetic surface. The temporal and spatial behaviour of these bunches is studied in some detail for the simple model of a tokamak with large aspect ratio. Possible implications of this phenomenon for diagnostics are discussed.