Electromagnetic radiation from upper-hybrid wave turbulence driven by electron beams in solar plasmas

Solar radio bursts of Type III are believed to result from a sequence of physical processes ultimately leading to electromagnetic wave emissions near the electron plasma frequency ω_p and its harmonic 2ω_p. The radiation bursts are due to energetic electron beams accelerated during solar flares. When propagating in the solar corona and the interplanetary wind, these fluxes excite Langmuir and upper-hybrid wave turbulence, which can be further transformed into electromagnetic radiation near the frequencies ω_p and 2ω_p.

It is believed that, in a homogeneous plasma, Langmuir turbulence evolves due to three-wave interaction processes, such as the fusion of Langmuir waves L with sound waves S leading to the formation of electromagnetic waves T_ωp at ω_p or the decay of L-waves into S-waves and T_ωp-waves. On the other hand, the electromagnetic waves radiated at 2ω_p should arise from the coalescence L + L’ --> T_2ωp of Langmuir waves L generated by the beam with Langmuir waves L’ coming from the electrostatic decay L --> L’ +  S.

Large-scale 2D3V Particle-In-Cell simulations have been performed with the fully kinetic code Smilei [Derouillat et al., 2018], using parameters typical of Type III solar radio busts. The excitation of upper-hybrid wave turbulence by energetic electron beams propagating in magnetized plasmas leads ultimately to electromagnetic emissions near the fundamental and the harmonic plasma frequencies.

Derouillat et al. , Comput. Phys. Commun., 222, 351, 2017.