Radiation emitter generated by interacting Langmuir waves

Radiation sources from Langmuir waves has been a topic of interest for their relevance to experimental approaches in plasma laboratories as well as for estimating physical models to explain cosmic radio bursts. Since the mechanism for converting energy from electrostatic Langmuir waves to electromagnetic waves is complex, diverse scenarios of such energy conversion have been studied, e.g. mode conversion, antenna radiation, nonlinear scattering, etc. Previously, we introduced a novel perspective of plasma dipole oscillation (PDO) which generates strong radiation bursts at the plasma frequency and high harmonics. In this paper, we report our discovery of radiation that result from electron-laser beam driven Langmuir waves and their interactions. In 2-D PIC simulations, we have observed that obliquely colliding Langmuir waves or even a single Langmuir wave generate localized radiation sources at the plasma frequency and high harmonics. These mechanisms differ from conventional two-plasmon mergers, where only the second harmonic of the plasma frequency is dominant: a strong radiation is observed even at the fundamental harmonic. In addition, from 3-D PIC simulations of electron laser beam driven plasma oscillators in magnetized plasma, the radiation from a local plasma oscillator, i.e. PDO, is found to be robust with diverse spectral peaks at the X-mode and the upper-hybrid mode. Nonlinear theory demonstrates that the relative strength of the harmonics of the plasma frequency depends on the shape of the PDO. The studies imply that the PDO has a more complicated internal structure than the simple model of a solid charge. We discuss the potential of the PDO generated from electron-beam driven plasmas or laser-driven plasmas as a radiation source and its relevance to cosmic radio bursts.