Electron Acceleration by Z-mode and Whistler-mode Waves Generated from an Electron Ring Distribution

Abstract:

We carried out a series of particle simulations to study electron acceleration by Z-mode and whistler-mode waves generated by an electron ring distribution. The electron ring distribution excites, through cyclotron maser process, the X-mode, Z-mode and whistler-mode waves. The X-mode wave propagates mainly in the perpendicular direction; the Z-mode wave in the perpendicular and the parallel directions; the whistler-mode wave mainly in the parallel direction. The parallel Z-mode and whistler-mode waves can further accelerate and diffuse the energetic electrons. The peak energy of the accelerated electrons can reach 2~8 times of the initial kinetic energy which ranges from 100 to 500 keV. We then study the acceleration process via test-particle calculations in which electrons interact with one wave, two counter-propagating waves or four counter-propagating waves. The electron trajectories in the one wave case are along simple diffusion curves. In the multi-wave cases, simultaneous acceleration of electrons by counter-propagating waves occurs, and electrons are accelerated efficiently. The strong acceleration in the multiwave cases is related to electron resonant trapping by waves, and wave phase velocity, amplitude and frequency play important roles.