Rapid Particle Acceleration by Large-Amplitude Magnetohydrodynamic Waves

我们研究了磁声波的非线性结构、电流驱动的不稳定性和粒子加速，特别注意了多物种离子的影响。这些结果已被应用于太阳高能粒子的研究。在含有两种离子的等离子体中，磁声波分裂成两个模：低频和高频模。当波数k趋于零时，低频模式的频率趋于零。另一方面，高频模式具有离子回旋频率量级的有限截止频率。然而，这两种模式可以用KdV方程来描述。这表明KdV方程并不局限于频率趋于零的k-gt；0的波。特征孤子宽度是低频模式的离子惯性长度和高频模式的电子惯性长度。在某些太阳耀斑中发生的富氦事件中，频率接近^3He回旋频率的波有望发挥重要作用。因此，我们研究了以氢和氦(^4He)回旋波为主要成分的等离子体中的电流驱动静电不稳定性。在这些研究的基础上，我们提出了太阳高能粒子的统一理论，它解释了平均化学成分、~3He丰度事件和离子加速到相对论能量。

We have studied nonlinear structure of magnetosonic waves, current driven instabilities, and particle acceleration, with special attention to effects of multi-species ions. These results have been applied to the investigation of solar energetic particles.In a plasma with two ion-species, a magnetosonic wave splits into two modes ; low- and high- frequency modes. The frequency of the low-frequency mode tends to zero as the wave number k approaches zero. On the other hand, the high-frequency mode has a finite cut-off frequency of the order of the ion cyclotron frequency. These two modes, however, are found to be described by KdV equations. This shows that KdV equations are not limited to the waves whose frequencies tend to zero as k->0. The characteristic solition widths are the ion inertal length for the low-frequency mode and the electron inertial length for the high-frequency mode.In ^3He-rich events occuring in some solar flares, the waves having frequencies close to the ^3He cyclotron frequency are expected to play an important role. Thus, we invesutigated current driven, electrostatic instabilities in a plasma whose main components are hydrogen and helium (^4He) cyclotron waves can be driven unstable with frequencies close to the ^3He cyclotron frequency.On the basis of these studies we proposed a unified theory for solar energetic particles that accounts for the mean chemical composition, ^3He-rich events, and prompt ion acceleration to relativistic energies.