Numerical study of resonant electron dynamics during the development of whistler instability

It has been suggested that whistler mode waves play an important role on accelerating electrons in Earth's radiation belts. In this study we investigated the dynamics of electrons interacting with whistler mode waves using a two-dimensional relativistic, electromagnetic Particle-In-Cell (PIC) code. Acceleration of electrons occurs by two different resonance mechanisms. For small values of whistler waves propagate obliquely across the background magnetic field, and significant part of the wave electric field is electrostatic. The electrostatic field can accelerate a portion of electrons along the magnetic field through Landau resonance. On the other hand, gyro-resonance can occur for some electrons by the right-handed polarized whistler waves and accelerate them perpendicular to the magnetic field. Interestingly, the two resonances become dominant over each other alternately in time. The electrons resonant with the whistler waves are initially located in specific regions in velocity space. Only a few percent of the total electrons resonantly interact with the waves. However, the resonant interaction produces supra-thermal tail along the velocity parallel to the magnetic field.