Nonlinear evolution of electromagnetic waves driven by the relativistic ring distribution

概要

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Relativistic ring distribution of plasma particles generates electromagnetic waves via the relativisticcyclotron resonance. The long time evolution of this so-called cyclotron maser instability at nullwave number (k50) is studied in detail, by performing particle simulations using a plasma whichconsists of relativistic ring electrons, background positrons, and background electrons. The linearand nonlinear stages of the system evolution are discussed for both gyrotropic and nongyrotropicring distributions. The linear theory predicts that, when the initial ring energy is strongly relativistic,there appears a critical initial ring momentum at which the system is marginally stable. Numericalsimulations show, however, that the system is nonlinearly unstable even when the initial ringmomentum exceeds the critical momentum. The final saturation level of the wave energy is obtainedanalytically.