Revisiting the theory of the evolution of pick-up ion distributions: magnetic or adiabatic cooling?
Revisiting the theory of the evolution of pick-up ion distributions: magnetic or adiabatic cooling?
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重新审视拾取离子分布演化理论：磁冷却还是绝热冷却？
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
H. Fahr
中科院分区：
文献类型：
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作者：
H. Fahr
抽象的。我们研究了日球层拾取离子在注入太阳风后的相空间行为，这些离子是由行星际中性原子的电荷交换或光电离产生的新离子。由于与环境MHD波场的相互作用，我们允许快速的俯仰角扩散，但在本文开始时，我们将忽略由逆流环境波引起的拟线性或非线性能量扩散(费米-2加速度)的影响。在目前有关太阳风对流拾离子的文献中，只考虑了这些离子的绝热冷却，它在太阳风框架中负责填补注入能量和太阳风离子热体能量之间的间隙。在这里，我们重新研究了绝热拾取离子反应这一假设背后的理论基础，以及由此得出的相关预测。然后，我们将其与新的假设进行了比较，该假设认为，拾取离子仅仅是由于它们被对流在行星际磁场中而产生的纯磁性冷却，而行星际磁场的大小随着太阳距离的增加而减小。我们比较了两种方法得到的拾取离子分布函数的结果，并可以指出观测和诊断相关性的本质区别。此外，我们还包括波粒相互作用的随机加速过程。正如我们所展示的，磁冷却与波粒相互作用的扩散加速相结合，允许一个不间断的幂定律，唯一的幂指数γ=−5从最低速度到大约100keV的最高能量粒子，它可以与磁声湍流略有共振。对由此产生的离子压力升高的后果也进行了分析。
Abstract. We study the phasespace behaviour of heliospheric pick-up ions after the time of their injection as newly created ions into the solar wind bulk flow from either charge exchange or photoionization of interplanetary neutral atoms. As interaction with the ambient MHD wave fields we allow for rapid pitch angle diffusion, but for the beginning of this paper we shall neglect the effect of quasilinear or nonlinear energy diffusion (Fermi-2 acceleration) induced by counterflowing ambient waves. In the up-to-now literature connected with the convection of pick-up ions by the solar wind only adiabatic cooling of these ions is considered which in the solar wind frame takes care of filling the gap between the injection energy and energies of the thermal bulk of solar wind ions. Here we reinvestigate the basics of the theory behind this assumption of adiabatic pick-up ion reactions and correlated predictions derived from it. We then compare it with the new assumption of a pure magnetic cooling of pick-up ions simply resulting from their being convected in an interplanetary magnetic field which decreases in magnitude with increase of solar distance. We compare the results for pick-up ion distribution functions derived along both ways and can point out essential differences of observational and diagnostic relevance. Furthermore we then include stochastic acceleration processes by wave-particle interactions. As we can show, magnetic cooling in conjunction with diffusive acceleration by wave-particle interaction allows for an unbroken power law with the unique power index γ=−5 beginning from lowest velocities up to highest energy particles of about 100 KeV which just marginally can be in resonance with magnetoacoustic turbulences. Consequences for the resulting pick-up ion pressures are also analysed.