Particle-In-Cell Simulations --- Ion Beam Instabilities and The Generation of Alfven and Whistler Waves in Low β Plasma*

Ion beam-driven instabilities in a  collisionless space plasma with  low β, i.e, low plasma and magnetic pressure ratio, are investigated using Particle-in-Cell (PIC) simulations. Specifically, the effects of different ion drift velocities on the development of Buneman and resonant electromagnetic (EM) right-handed (RH) ion beam instabilities are studied. Our simulations reveal that both instabilities can be driven when the ion beam drift exceeds the theoretical thresholds. The Buneman instability, which is weakly triggered initially,  dissipates only a small fraction of the kinetic energy of the ion beam while causing significant electron heating, owing to the small electron-ion mass ratio. However, we find that the ion beam-driven Buneman instability is quenched effectively by the resonant EM RH ion beam instability.  Instead, the resonant EM RH ion beam instability dominates when the ion drift velocity is larger than the Alfven speed, leading to the generation of RH Alfven waves and RH whistler waves. We find that the intensity of Alfven waves decreases with decrease of ion beam drift velocity, while the intensity of whistler waves increases. Our results provide new insights into the complex interplay between ion beams and plasma instabilities in low β collisionless space plasmas.