Simulation of Electromagnetic Emission near the Plasma Frequency from Relativistic Electron Beams : Fluids, Plasmas, and Electric Discharges

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Using a two-dimensional electromagnetic and relativistic particle-in-cell (PIC) code, we show that electromagnetic waves are excited with near fundamental plasma frequency and its second harmonics from relativistic electron beam instability, whose beam velocity is 0.8c. It is also shown that electromagnetic waves with second harmonics can be emitted with a short time delay from the beam instability and the second harmonic waves are extraordinary waves (X-mode) propagating nearly perpendicular to an ambient magnetic field. By changing the beam velocity from 0.5c to 0.8c, we found that the second harmonics can make transition from R-mode like wave to X-mode. The emission mechanism of the second harmonics with X-mode characteristics is a new nonlinear process, in which the proton dynamics does not contribute at all, in contrast to the conventional three waves process. We discuss a possible emission mechanism for the present simulation result.
社団法人日本物理学会の論文
2001-04-15