Turbulence-level dependence of cosmic ray parallel diffusion
Turbulence-level dependence of cosmic ray parallel diffusion
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DOI：
10.1093/mnras/staa2533
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发表时间：
2020-09
影响因子：
4.8
通讯作者：
P. Reichherzer;P. Reichherzer;J. Tjus;E. Zweibel;L. Merten;L. Merten;M. Pueschel
中科院分区：
文献类型：
--
作者：
P. Reichherzer;P. Reichherzer;J. Tjus;E. Zweibel;L. Merten;L. Merten;M. Pueschel
了解高能宇宙射线的传输属于天体物理学中最具挑战性的课题。电磁涨落散射引起的扩散是宇宙线输运中的一个关键过程。从弹道到扩散传播制度的过渡是在直接数值计算的扩散系数均匀磁场线受到湍流扰动。模拟结果与理论推导的平行扩散系数的依赖关系的能量和波动幅度在弱湍流的限制。本研究表明，广泛使用的外推的能量标度的平行扩散系数的高湍流水平的准线性理论预测的共振散射制度不提供一个普遍准确的描述。这里强调的是，数值计算的扩散系数可以污染的低能量，由于缺少共振相互作用的粒子与湍流的可能性。五个减少刚度制度的建立，这是由本工作中推导出的分析边界分开。因此，宇宙线传播的正确描述只能通过使用依赖于能级的扩散系数来实现，并有助于解决银河系宇宙线梯度问题。
Understanding the transport of energetic cosmic rays belongs to the most challenging topics in astrophysics. Diffusion due to scattering by electromagnetic fluctuations is a key process in cosmic-ray transport. The transition from a ballistic to a diffusive-propagation regime is presented in direct numerical calculations of diffusion coefficients for homogeneous magnetic field lines subject to turbulent perturbations. Simulation results are compared with theoretical derivations of the parallel diffusion coefficient's dependencies on the energy and the fluctuation amplitudes in the limit of weak turbulence. The present study shows that the widely-used extrapolation of the energy scaling for the parallel diffusion coefficient to high turbulence levels predicted by quasi-linear theory does not provide a universally accurate description in the resonant-scattering regime. It is highlighted here that the numerically calculated diffusion coefficients can be polluted for low energies due to missing resonant interaction possibilities of the particles with the turbulence. Five reduced-rigidity regimes are established, which are separated by analytical boundaries derived in the present work. Consequently, a proper description of cosmic-ray propagation can only be achieved by using a turbulence-level-dependent diffusion coefficient and can contribute to solving the Galactic cosmic-ray gradient problem.