Generation and Evolution of Fluctuations in a Non-equilibrium Solar Wind Plasma

对太阳风等离子体微态的长期调查表明，微态与观测到的涨落有直接关系，表明后者是由动力学不稳定性在局部产生和放大的。低能(核)布居接近能量均分，并被限制在由动力学不稳定性阈值形成的温度各向异性的范围内。然而，对于超热粒子群来说，这个谜题仍然没有解决，尽管它们包含了显著的动能密度，即使在没有动力学各向异性的情况下，也保持了空间等离子体的热平衡。在拟议的为期3年的项目中，我们将前所未有地详细调查核心和晕群之间的相互作用，这似乎对等离子体波动的产生和演变具有决定性作用。主要目的是为实际预测和描述由太阳风中的动力学各向异性引起的等离子体波动提供理论基础。这将通过使用广义Kappa分布函数在动力学水平上模拟各向异性等离子体状态来实现，广义Kappa分布函数是自洽描述太阳风等离子体动力学的先进而有力的工具。在线性理论框架内确定的不稳定性条件和最大生长速率尤为重要，它们将揭示动力学各向异性最快的弛豫过程。将特别注意电子和质子的相互作用，因为它们可以显著改变不稳定条件，以及通常被忽略但似乎比周期模更有效的弱传播和非周期涨落。提出的研究方案包括首次对各向异性Kappa分布等离子体中自生微不稳定性的准线性(弱非线性)演化进行分析和数值研究。这使得能够全面研究涨落的线性和非线性演化，包括它们对速度分布和力矩的反向反应，即对宏观等离子体参数的影响。鉴于目前对非平衡等离子体物理学的普遍兴趣，并鉴于过去、当代、特别是即将进行的航天器飞行任务的大量观测数据提供了增进我们对这类等离子体的理解的机会，该项目非常及时。

Long-term surveys of the solar wind plasma microstates have revealed a direct correlation with observed fluctuations, pointing to a local generation and amplification of the latter by the kinetic instabilities. The low-energy (core) populations are close to an energy equipartition and constrained within the limits of temperature anisotropy shaped by the thresholds of the kinetic instabilities. However, this puzzle is still unresolved for the suprathermal populations, although they comprise a significant kinetic energy density and maintain the space plasmas out of thermal equilibrium even in the absence of kinetic anisotropies. Within the proposed 3-year project we will investigate in unprecedented detail the interplay of the core and halo populations that appears to be decisive in the generation and evolution of plasma fluctuations. The main goal is the formulation of a theoretical basis for a realistic prediction and characterization of plasma fluctuations induced by the kinetic anisotropies in the solar wind. This will be achieved by modeling the anisotropic plasma states on the kinetic level using generalized Kappa distribution functions, which represent an advanced powerful tool to self-consistently describe the solar wind plasma dynamics. The instability conditions and the maximum growth rates determined within the framework of the linear theory are particularly important and will unveil the fastest relaxation process of the kinetic anisotropy. Special attention will be given both to the mutual effects of electrons and protons as these can significantly change the instability conditions, and to the weakly propagating and aperiodic fluctuations which are usually ignored but appear to be more efficient than periodic modes. The proposed research programme comprises the first analytical and numerical investigation of the quasilinear (weakly-nonlinear) evolution of the self-generated microinstabilites in anisotropic Kappa distributed plasmas. This enables a comprehensive study of the linear and nonlinear evolution of fluctuations, including their back reaction on the velocity distributions and on their moments, i.e. on the macroscopic plasma parameters. This project is very timely in view of the present general interest in physics of non-equilibrium plasmas, as well as in view of the opportunities to advance our understanding of such plasmas offered by a large amount of observational data from passed, contemporary and, particularly, of forthcoming spacecraft missions.