Energy transfer to heavy ions by nonlinear evolution of current-driven instabilities in a multi-ion-species plasma

Current-driven instabilities and associated energy transport among different particle species in a plasma consisting electrons and hydrogen (H) and helium (He) ions are studied theoretically and numerically. First, a theory predicting the dominant unstable modes is developed. Theoretical estimates of energy, gains of ions from the waves are also obtained. Next, by means of a three-dimensional electrostatic particle code with full ion and electron dynamics, the nonlinear evolution of the instabilities and the energy transfer to ions are further investigated. Simulations show that the second harmonic H cyclotron wave with parallel phase velocity equal to the initial electron drift speed eventually becomes dominant owing to the change in the electron velocity distribution function. The observed heating rate of He ions by the dominant wave is much greater than that of H ions. These simulation results are in good agreement with the theory.