Nonlinear Evolution of Ion-Cyclotron Turbulence Generated by Artificial Plasma Cloud Release

Nonlinear evolution of plasma turbulence generated by a plasma cloud released into a magnetized background plasma is studied using electromagnetic hybrid (fluid electrons and particle ions) plasma simulations incorporating electron inertia. The turbulence considered is generated from free energy in an assumed ring velocity distribution in the released plasma cloud heavy ions. The turbulence initially lies near harmonics of the ring plasma ion cyclotron frequency and propagates nearly perpendicular to the background magnetic field as predicted by linear theory. If the amplitude of the turbulence is sufficiently large, the relatively short wavelength ion cyclotron waves evolve nonlinearly into much longer wavelength obliquely propagating shear Alfven waves. The results indicate that ring densities above a few percent of the background plasma density may produce wave amplitudes large enough for such an evolution to occur. The extraction of energy from the ring plasma may be in the range of 10-20% with a slight decrease in the magnitude as the ring density is increased from a few percent to several 10’s of percent of the background plasma density. Suitability of the nonlinearly generated shear Alfven waves for applications to scattering radiation belt particles is discussed.