Saturation of trapped-ion instability by two-dimensional electrostatic trapping

The non-linear evolution of trapped-ion instability in Tokamaks is investigated. The authors first derive a kinetic model of mode coupling, but show that it cannot be readily applied to resonant curvature-driven modes. They then show that non-linear saturation can result from trapping of resonant particles in the electrostatic potential of the wave. This mechanism is strongly enhanced by the radial structure of the mode, resulting in very low amplitudes at saturation.