Particle-in-cell simulation study of the parametric instabilities and turbulence of Alfven-ion-cyclotron waves in a low-beta plasma

Abstract

Parametric instabilities of Alfven-ion-cyclotron (AIC) waves and the turbulence driven by them are investigated using a particle-in-cell simulation technique. By introducing anisotropic ion temperature, a broad spectrum of AIC wave is excited. In addition to the normal AIC waves, their harmonic modes and upper sideband modes are found. Through the interaction of these Alfvenic waves and longitudinal electrostatic waves, Alfvenic turbulence is developed. Excitation of density and electromagnetic waves and their mode coupling structures are investigated using the omega-k spectrum and bicoherence analysis. It is found that the ion-acoustic wave is excited by the modulational instability, and that the ion density mode with a negative group velocity is excited in the high-k region by the decay instability. In addition, a longitudinal mode whose phase velocity behaves similarly to that of the ion-acoustic mode with a shifted wave number is found. This mode is identified as the second harmonic ion-acoustic wave. The inverse cascade structures of the electromagnetic and density fluctuations exhibit an interesting behavior that the density fluctuation shows a dual spectrum, whereas the electrostatic field E-x shows a single spectrum.