Wave–particle interactions in marginally unstable plasma as a means of energy transfer between energetic particle populations

Energy exchange between waves and resonant (usually energetic) particles is an essential feature of wave–particle interactions in plasma. If the resonant interaction in a magnetized unstable plasma involves two or more cyclotron resonances, the wave excitation can, at the same time, mediate the energy transfer between different populations of energetic particles. This effect, which is particularly pronounced in a marginally unstable plasma, is discussed by example of whistler–electron interactions in connection with particle energization in the Earthʼs radiation belts. The process under discussion is similar, although not identical, to alpha channeling known in the physics of tokamak plasma.

► Slowly growing wave mediates essential energy transfer between particle populations.
► Increase of resonant particle energy density greatly exceeds the wave energy density.
► Energy source for particle acceleration is not the wave but other resonant particles.