Dispersion relation as a channel of plasma turbulence evolution

Abstract

We present evidence from ion-scale plasma turbulence simulations that normal-mode waves and sideband waves co-exist when a plasma evolves from wave fields into turbulence. Ion-scale fluctuations represent normal-mode fluctuations such as Bernstein and cyclotron modes, accompanied by sideband waves having moderate frequency mismatch with the normal modes. The evolution process is studied using the method of energy partition and frequency broadening. Wave evolution into turbulence exhibits distinct stages: growth phase of normal modes, saturation, and decay. The saturation time is of the order of 1000 ion gyroperiods, which is delayed at higher values of the plasma parameter beta. We conclude that the dispersion relations play the central role in plasma turbulence evolution, serving as the energy flux channel in the spectral domain.