This paper describes a conceptual framework for understanding kinetic plasma turbulence as a generalized form of energy cascade in phase space. It is emphasized that conversion of turbulent energy into thermodynamic heat is only achievable in the presence of some (however small) degree of collisionality. The smallness of the collision rate is compensated for by the emergence of a small-scale structure in the velocity space. For gyrokinetic turbulence, a nonlinear perpendicular phase-mixing mechanism is identified and described as a turbulent cascade of entropy fluctuations simultaneously occurring at spatial scales smaller than the ion gyroscale and in velocity space. Scaling relations for the resulting fluctuation spectra are derived. An estimate for the collisional cutoff is provided. The importance of adequately modelling and resolving collisions in gyrokinetic simulations is briefly discussed, as well as the relevance of these results to understanding the dissipation-range turbulence in the solar wind and the electrostatic microturbulence in fusion plasmas.
本论文描述了一个概念框架，将动理学等离子体湍流理解为相空间中的广义能量级联。文中强调，湍流能量向热力学热量的转换只有在存在某种（无论多小的）碰撞性的情况下才能实现。碰撞率的微小性由速度空间中小尺度结构的涌现所补偿。对于回旋动理学湍流，本文识别并描述了一种非线性垂直相混合机制，将其视为熵涨落的级联，该级联同时发生在小于离子回旋半径的空间尺度和速度空间中。文中推导了由此产生的涨落谱的标度关系，并给出了碰撞截断的估计。本文还简要讨论了在回旋动理学模拟中适当建模和解析碰撞的重要性，以及这些结果对于理解太阳风中的耗散范围湍流和聚变等离子体中的静电微观湍流的相关性。