Simulation of Multiple Harmonic Electromagnetic Radiation

Electromagnetic radiation at the plasma frequency and/or its second harmonic, the so-called plasma emission, is widely believed to be the fundamental process responsible for solar type II and type III radio bursts. The traditional theory based upon weak turbulence three-wave and nonlinear wave-particle interaction processes predicts radiation emission primarily at the fundamental and the second harmonic of the plasma frequency. On the other hand, recent theory and one-dimensional electrostatic particle-in-cell computer simulation of beam-plasma interaction demonstrate that multiple harmonics of electrostatic plasma oscillation frequency can be excited. The question of whether these electrostatic multiple harmonics contribute to the escaping radiation or not has not been conclusively resolved since the simulation results available thus far are confined to electrostatic limit. In the present discussion, two-dimensional electromagnetic particle-in-cell simulation of beam-plasma interaction process is performed. The result shows that long-wavelength electromagnetic radiation is generated at multiple harmonics of plasma frequency, which is distinct from the electrostatic counterpart by its long wavelength (or equivalently, small wave numbers). This indicates that the traditional picture of plasma emission process must be modified to include higher (i.e., third, fourth, and so forth) harmonic radiation. The accompanying paper (Yi et al) proposes a theoretical explanation.