Waves and Instabilities
Waves and Instabilities
复制标题
波浪和不稳定性
DOI：
10.1007/978-3-642-75364-0_4
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
D. Gurnett
中科院分区：
文献类型：
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作者：
D. Gurnett
人们普遍认为，尽管太阳风在本质上是无碰撞的，但在很好的近似情况下，它可以被视为流体。要理解这一行为，首先必须了解控制等离子体宏观性质的微观过程。在无碰撞的等离子体中，如太阳风，现在人们普遍认识到，波的作用类似于普通流体中的碰撞。当等离子体从太阳向外流动时，动力学变化导致速度分布函数偏离平衡热分布。在没有碰撞的情况下，这些偏差继续增长，直到平行和垂直于磁场的速度-空间梯度∂f/∂v||和∂f/∂v⊥变得如此大，以至于开始出现等离子体不稳定性。这些不稳定性导致了海浪的增长。当波增长到大振幅时，波-粒子相互作用最终消除了导致不稳定的速度-空间梯度。因此，波动和不稳定性在防止大的偏离热平衡方面起着至关重要的作用。对于等离子体中可能发生的等离子体不稳定性和波-粒子相互作用的类型的回顾，例如参见长谷川[9.34]或梅尔罗斯[9.47]。
It is widely recognized that even though the solar wind is essentially collisionless, to a good approximation it can be treated as a fluid. To understand this behavior, it is first necessary to understand the microscopic processes that control the macroscopic properties of the plasma. In a collisionless plasma such as the solar wind, it is now widely recognized that waves play a role similar to collisions in an ordinary fluid. As the plasma flows outward from the sun, dynamical changes cause the velocity distribution function to deviate from an equilibrium thermal distribution. In the absence of collisions these deviations continue to grow until the velocity-space gradients parallel and perpendicular to the magnetic field, ∂f/∂v||and ∂f/∂v⊥become so large that plasma instabilities start to occur. These instabilities lead to the growth of waves. As the waves grow to large amplitudes, wave-particle interactions eventually act to eliminate the velocity- space gradients that cause the instability. Waves and instabilities thereby play a crucial role in preventing large deviations from thermal equilibrium. For a review of the types of plasma instabilities and wave-particle interactions that can occur in a plasma see, for example, Hasegawa [9.34], or Melrose [9.47].