Explosive Instabilities in Simulated Plasmas

Nonlinear instabilities arising from the interaction of two positive energy waves and one negative energy wave have been observed on a one-dimensional superparticle computer model for perpendicularly propagating, linearly stable cyclotron waves. For the case in which all three-wave amplitudes are initially equal, the theoretical predictions and experimental results on the growth of these instabilities are in good qualitative and quantitative agreement. Saturation is observed when the electrostatic energy grows to about 1% of the kinetic energy in the system, sufficient to cause significantly large changes in the equilibrium orbits. The “forward scattering” theory of Fukai, Krishan, and Harris is used to explain the qualitative behavior of the wave amplitudes and phases just prior to saturation.