论文标题
在太阳风的温度下
On the temperature of the solar wind
论文作者
论文摘要
太阳风提供了一个弱碰撞等离子体在存在空间差异磁场线的情况下从热源扩展的示例。观察结果表明，在内部的地球层中，电子温度的距离大约为$ t_ {e}（r）\ sim r^{ - 0.3} \ dots r^{ - 0.7} $，比绝热膨胀法$ \ sim r^sim r^{ - 4/4/3} $明显慢得多。在这种观察结果的推动下，我们提出了一种动力学理论，该理论解决了从中央热源扩展的几乎无碰撞血浆的非绝热演化。我们集中于沿着径向散开的磁通管传播的能量电子的动力学。由于其磁矩的保存，电子形成沿磁场线准直的光束。由于能量与背景等离子体的交换弱，光束种群逐渐失去其能量并加热背景血浆。我们建议，无论碰撞多么弱，在距来源的足够远的地方都建立了通用的扩展状态，在电子温度下降为$ t_e（r）\ propto r^{ - 2/5} $。这接近于内部地球内太阳风温的观察到的尺度。因此，我们的第一本动力学推导可能会为太阳风中的可绝化温度降低而提供解释。更广泛地说，它对于描述G型星的磁性风很有用。
Solar wind provides an example of a weakly collisional plasma expanding from a thermal source in the presence of spatially diverging magnetic field lines. Observations show that in the inner heliosphere, the electron temperature declines with the distance approximately as $T_{e}(r)\sim r^{-0.3} \dots r^{-0.7}$, which is significantly slower than the adiabatic expansion law $ \sim r^{-4/3}$. Motivated by such observations, we propose a kinetic theory that addresses the non-adiabatic evolution of a nearly collisionless plasma expanding from a central thermal source. We concentrate on the dynamics of energetic electrons propagating along a radially diverging magnetic flux tube. Due to the conservation of their magnetic moments, the electrons form a beam collimated along the magnetic field lines. Due to weak energy exchange with the background plasma, the beam population slowly loses its energy and heats the background plasma. We propose that no matter how weak the collisions are, at large enough distances from the source a universal regime of expansion is established where the electron temperature declines as $T_e(r)\propto r^{-2/5}$. This is close to the observed scaling of the solar wind temperature in the inner heliosphere. Our first-principle kinetic derivation may thus provide an explanation for the slower-than-adiabatic temperature decline in the solar wind. More broadly, it may be useful for describing magnetized winds from G-type stars.
