Electrostatic Decay of Beam-generated Plasma Turbulence

The study of the evolution of a suprathermal electron beam traveling through a background plasma is relevant to the physics of solar flares and their associated type III solar radio bursts. As they evolve, guided by the coronal magnetic field lines, these beams generate Langmuir turbulence. The beam-generated turbulence is in turn responsible for the emission of radio photons at the second harmonic of the local plasma frequency, which are observed during type III solar radio bursts. To generate the radio emission, the beam-aligned Langmuir waves must coalesce, and therefore, a process capable of redirecting the turbulence in an effective fashion is required. Different theoretical models identify the electrostatic (ES) decay process L₁ → L₂ + S (where L indicates a Langmuir wave and S an ion-acoustic wave) as the redirecting mechanism for the L waves. Two different regimes have been proposed to play a key role: backscattering and diffusive (small-angle) scattering. This paper is a comparative analysis of the ES decay rate for each regime and of the different observable characteristics that are expected for the resulting ion-acoustic waves.