Stochastic Acceleration of ∼0.1–5 keV Pickup Ions in the Heliotail
Stochastic Acceleration of ∼0.1–5 keV Pickup Ions in the Heliotail
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DOI：
10.3847/1538-4357/aac3de
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发表时间：
2018-06
期刊：
影响因子：
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通讯作者：
E. Zirnstein;R. Kumar;J. Heerikhuisen;D. McComas;A. Galli
中科院分区：
文献类型：
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作者：
E. Zirnstein;R. Kumar;J. Heerikhuisen;D. McComas;A. Galli
我们试图了解的主导物理过程（电荷交换，绝热加热，随机加速）的定量作用，管理的质子分布在heliotail使用观测的氢高能中性原子（ENA）从星际边界探测器（IBEX）。我们解决太阳风质子和拾取离子（PUI）的帕克输运方程，因为它们从终端冲击波（TS）传播下来的日尾，包括质子和中性氢原子之间的电荷交换源项来自磁流体和动力学中性模拟的日光层。我们计算ENA通量在1 Au的质子输运模型的结果，并将它们与IBEX观测。我们发现，在我们的模型的假设下，一个随机的加速过程是需要抵消的能量依赖的损失的10.1 -5 keV的PUI从电荷交换再现IBEX数据。扩散系数（光谱指数γ）的幂律速度依赖性限于0.67 < γ < 2的范围，与IBEX数据的最佳拟合似乎接近γ <1.25。扩散速率约为1.1 × 10−8 km 2 s−3（v/v0）1.25，几乎可以平衡电荷交换造成的0.1-5 keV PUI损失。我们的分析表明，回旋共振与两个广为人知的不可压缩MHD湍流：即各向同性Kolmogorov和各向异性Goldreich-Sridhar湍流，以及随机粒子与压缩波的相互作用本身不是占主导地位的扩散机制。然而，由于PUI的存在，可能会发生一些中间过程。
We seek to understand the quantitative role of the dominant physical processes (charge-exchange, adiabatic heating, stochastic acceleration) governing the proton distribution in the heliotail using observations of hydrogen energetic neutral atoms (ENAs) from the Interstellar Boundary Explorer (IBEX ). We solve the Parker transport equation for solar wind protons and pickup ions (PUIs) as they propagate from the termination shock (TS) down the heliotail, including charge-exchange between protons and neutral hydrogen atoms as source terms derived from an MHD-fluid and kinetic-neutral simulation of the heliosphere. We compute ENA fluxes at 1 au from the results of the proton transport model and compare them with IBEX observations. We find that, under the assumptions of our model, a stochastic acceleration process is needed to counteract the energy-dependent losses of ∼0.1–5 keV PUIs from charge-exchange to reproduce IBEX data. The power-law velocity dependence of the diffusion coefficient (spectral index γ) is limited to the range 0.67 < γ < 2, and the best fit to IBEX data appears close to γ ∼ 1.25. The diffusion rate ∼1.1 × 10−8 km2 s−3 (v/v0)1.25 nearly balances the loss of ∼0.1–5 keV PUIs by charge-exchange. Our analysis suggests that cyclotron resonance with two widely known incompressible MHD turbulence: namely, isotropic Kolmogorov and anisotropic Goldreich–Sridhar turbulence, as well as stochastic particle interactions with compressive waves are not by themselves the dominant diffusion mechanisms. However, some intermediate processes may be occurring due to the presence of PUIs.