Particle acceleration and nonlinear phenomena in a multi-ion-species plasma

点击翻译按钮获取中文摘要

Most of the fusion and space plasmas contain multiple ion species. Through theory and simulation, we have studied instabilities, nonlinear wave propagation, and particle acceleration in plasmas, giving particular attention to effects of the presence of multiple ion species.In a two-ion-species plasma, the magnetosonic wave is split into two modes ; the low- and high-frequency modes. Even though the high-frequency mode has a finite cutoff frequency, we derived KdV equations for both of these two modes. Their nonlinear behaviors were further studied through computer simulation based on a three-fluid model.By using a relativistic particle simulation code, we found that a magnetosonic wave can accelerate heavy ions by a mechanism different from that of hydrogen acceleration. All the heavy ions are accelerated, and their maximum speeds are about the same. This can explain the mean elemental composition of solar energetic particles.The heavy ion acceleration takes place even in small-ampitude waves. Thus, in a multi-ion-species plasma, even a small-amplitude perpendicular magnetosonic pulse is damped. Theoreti-cally obtained damping rate was in good agreement with simulation results.We also investigated current-driven instabilities in multi-ion-species plasmas. It was shown that some instabilities can cause ^3He-rich events and associated enhancements of heavy ions in high-energy particles.Large-amplitude magnetosonic waves with relativistic propagation speeds were studied. Magnetic and electric field strengths were obtained as a function of propagation speed.