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 differen t particle species in a plasma consisting electrons and hydrogen (H) and he lium (He) ions are studied theoretically and numerically. First, a theory p redicting the dominant unstable modes is developed. Theoretical estimates o f 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 tran sfer to ions are further investigated. Simulations show that the second har monic H cyclotron wave with parallel phase velocity equal to the initial el ectron drift speed eventually becomes dominant owing to the change in the e lectron velocity distribution function. The observed heating rate of He ion s by the dominant wave is much greater than that of H ions. These simulatio n results are in good agreement with the theory.