Superthermal radiation from tokamak plasmas caused by cyclotron magnetoacoustic instability

The electromagnetic power in the ion cyclotron frequency range radiated by a tokamak plasma with energetic ions is considered. It is found that the radiation may result from plasma fluctuations which are associated with the edge localized fast magnetoacoustic eigenmodes and strongly enhanced by interaction with the energetic ions. In this case, almost all the energy transferred from the energetic particles to the waves is emitted by the plasma and the system is marginally stable due to the presence of small wave damping. In particular, this picture is consistent with the power measurements of superthermal ion cyclotron emission in the JET preliminary tritium experiment.