We study the cyclotron maser instability (CMI) driven by an energetic ring-beam distribution by a particle simulation to explain possible generation mechanisms of intense radiation phenomena observed in space. The main objective is to understand the nonlinear processes that control saturation of the emission process. Our study reveals new issues that have been overlooked in past literature. It is found that electrostatic wave modes excited by the electron beam instability compete with the electromagnetic waves excited by the CMI. Nonlinear effects of these electrostatic modes tend to redistribute the energy of the energetic electrons and make the physics more complicated. The CMI can be much less effective in a realistic case than it is anticipated theoretically.
We demonstrate by a particle simulation that Z-mode waves generated by the cyclotron maser instability can lead to a significant acceleration of energetic electrons. In the particle simulation, the initial electron ring distribution leads to the growth of Z-mode waves, which then accelerate and decelerate the energetic ring electrons. The initial ring distribution evolves into an X-like pattern in momentum space, which can be related to the electron diffusion curves. The peak kinetic energy of accelerated electrons can reach 3 to 6 times the initial kinetic energy. We further show that the acceleration process is related to the "nonlinear resonant trapping" in phase space, and the test-particle calculations indicate that the maximum electron energy gain De max is proportional to B 0:57 w , where B w is the wave magnetic field.
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