Nonlinear stabilization of single, resonant, loss-cone flute instabilities

The evolution of linearly unstable, high-frequency (ω≈nΩ), flutelike (k‖ = 0), electrostatic modes which can occur in a multicomponent, magnetic-mirror-confined collisionless plasma has been studied by computer simulation using a one-and-one-half dimensional model. Approximately one-quarter of the particles in the initial velocity distributions formed a warm, Maxwellian background component; the remainder belonged to a hot, linearly stable, loss-cone component. The early evolution of single wave (either traveling or standing), resonant instabilities agrees well with linear theory. A rapid, coherent heating of the warm component occurs and spatial harmonics of the unstable wave appear. The electrostatic field of the wave then saturates at an energy level as much as two orders of magnitude lower than those reported in previous simulation studies of the same and related instabilities or predicted from earlier nonlinear analysis. The saturation levels and early post-saturation behavior are in agreement with a recently reported nonlinear analysis which was motivated by the results reported here.