Electron heat flow in the solar corona: Implications of non‐Maxwellian velocity distributions, the solar gravitational field, and Coulomb collisions
Electron heat flow in the solar corona: Implications of non‐Maxwellian velocity distributions, the solar gravitational field, and Coulomb collisions
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日冕中的电子热流：非麦克斯韦速度分布、太阳引力场和库仑碰撞的影响
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发表时间：
2003
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通讯作者：
J. Scudder
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作者：
J. Dorelli;J. Scudder
[1]人们早就知道，在完全电离的等离子体中，弱的电子温度梯度（满足λ ε Te ε/Te ε 10−4，其中λe是电子平均自由程，Te是电子温度）会导致电子速度分布上出现明显的非麦克斯韦超热尾，从而使Spitzer和Harm [1953]微扰理论失效[Gray和Kilkenny，1980; Bell等人，1981; Scudder和Olbert，1983]。在本文中，我们工作的影响，这种非局部热流的电子在太阳日冕，比较一个新的分析理论的数值解的福克-普朗克方程。虽然电子-电子库仑碰撞在日冕密度下足以影响局部温度，但电子热通量由基本上无碰撞的高能尾部决定。超热电子在极化电场中的减速使电子热逆着局部温度梯度径向向外流动，这与局部热力学平衡图相反，在局部热力学平衡图中，热被约束沿着局部温度梯度向下流动。我们讨论了这种效应的影响日冕加热机制的经验约束。
[1] It has long been known that weak electron temperature gradients in fully ionized plamas (satisfying λ ∣∇Te∣/Te ≲ 10−4, where λe is the electron mean free path and Te is the electron temperature) can lead to the development of significant non-Maxwellian suprathermal tails on electron velocity distributions, invalidating the Spitzer and Harm [1953] perturbation theory [Gray and Kilkenny, 1980; Bell et al., 1981; Scudder and Olbert, 1983]. In this paper we work out the implications of such nonlocal heat flow for electrons in the solar corona, comparing a new analytical theory to numerical solutions of the Fokker-Planck equation. While electron-electron Coulomb collisions are strong enough at coronal densities to influence the local temperature, the electron heat flux is determined by the essentially collisionless high-energy tail. The deceleration of suprathermal electrons in the polarization electric field allows electron heat to flow radially outward against the local temperature gradient, in contrast to the local thermodynamic equilibrium picture, in which heat is constrained to flow down the local temperature gradient. We discuss the implications of this effect for empirical constraints of coronal heating mechanisms.