论文标题
背景湍流对空间等离子体中离子温度各向异性松弛的影响
Effects of the Background Turbulence on the Relaxation of Ion Temperature Anisotropy in Space Plasmas
论文作者
论文摘要
空间等离子体中的湍流通常表现出两种由光谱中断分开的机制，这些频谱断裂将所谓的惯性和动力学范围分开。在-5/3或-2斜率幂律频谱之后，大规模磁波动以非线性MHD波波相互作用为主。休息后，在发生动力学效应的尺度上，磁频谱遵循较陡峭的幂律$ k^{ - α} $形状，由光谱指数$α> 5/3 $给出。尽管它无处不在，但通常不考虑湍流背景光谱在太阳风温的准线性松弛中的可能影响。在这项工作中，一种准线性动力学理论用于研究最初由冷电子和双 - 麦克斯威尔质子组成的最初湍流无孔的血浆中质子温度的演变，其中电磁波沿着背景磁场传播。将四个波光谱形状与不同水平的波强度进行比较。我们表明，足够的湍流磁力可以驱动稳定的质子横向加热，从而导致温度各向异性的升高和平行质子β的还原。因此，稳定的质子速度分布可以以发展动力学不稳定性的方式发展。这可以解释为什么可以观察到太阳风的成分远离热力学平衡和靠近不稳定性阈值。
Turbulence in space plasmas usually exhibits two regimes separated by a spectral break that divides the so called inertial and kinetic ranges. Large scale magnetic fluctuations are dominated by non-linear MHD wave-wave interactions following a -5/3 or -2 slope power-law spectrum. After the break, at scales in which kinetic effects take place, the magnetic spectrum follows a steeper power-law $k^{-α}$ shape given by a spectral index $α> 5/3$. Despite its ubiquitousness, the possible effects of a turbulent background spectrum in the quasilinear relaxation of solar wind temperatures are usually not considered. In this work, a quasilinear kinetic theory is used to study the evolution of the proton temperatures in an initially turbulent collisionless plasma composed by cold electrons and bi-Maxwellian protons, in which electromagnetic waves propagate along a background magnetic field. Four wave spectrum shapes are compared with different levels of wave intensity. We show that a sufficient turbulent magnetic power can drive stable protons to transverse heating, resulting in an increase in the temperature anisotropy and the reduction of the parallel proton beta. Thus, stable proton velocity distribution can evolve in such a way as to develop kinetic instabilities. This may explain why the constituents of the solar wind can be observed far from thermodynamic equilibrium and near the instability thresholds.
