Formation of quasi-power law weak Langmuir turbulence spectrum by harmonic generation

Abstract

Abstract. Langmuir wave turbulence generated by a beamplasma interaction has been studied since the early days of plasma physics research. Despite a long history of investigation on this subject, among the outstanding issues is the generation of harmonic Langmuir waves observed in both laboratory and computer-simulated experiments. However, the phenomenon has not been adequately explained in terms of theory, nor has it been fully characterized by means of numerical simulations. In this paper, a theory of harmonic Langmuir wave generation is put forth and tested against the Vlasov simulation results. It is found that the harmonic Langmuir mode spectra exhibit quasi power-law feature implying a multi-scale structure in both frequency and wave number space spanning several orders of magnitude.

Nonlinear Interaction Between H+ Band and He+ Band EMIC Waves: Van Allen Probe Observations and Hybrid Simulations

“…In fact, the pump wave and its harmonics constitute a weak turbulence system, in which the power of the harmonics will finally be determined by the pump waves (if the background plasma environment is fixed). That is, though the third harmonic is generated via the resonance between the second harmonic and pump wave, its saturated power depends only on the pump wave because the second harmonic itself is strongly associated with the pump wave (e.g., Fal'kovich & Shafarenko, 1988; Yoon, 2004). However, in this paper, the third emission depends on two independent ion cyclotron waves, though it is also resulted from a three‐wave resonance.…”