Diffusive shock acceleration of cosmic rays with non-Gaussian transport

扩散激波加速(DSA)被认为是最有可能产生观测到的宇宙线幂定律谱的加速过程。DSA的关键因素之一是MHD湍流对宇宙射线的散射，据信上游和下游都存在激波。虽然过去对DSA的研究大多采用准线性模型来描述宇宙线的空间扩散，但宇宙线在具有MHD湍流的等离子体中的实际输运可能会有本质上的不同。我们通过指定宇宙线的非高斯型散射统计，通过测试粒子模拟来研究DSA过程。对宇宙线谱、空间分布和加速时间尺度进行了估算，并与观测数据进行了比较。此外，还对含激波的分形扩散方程进行了数值计算，并与试验粒子模拟结果进行了比较。

The diffusive shock acceleration (DSA) is recognized as the most likely acceleration process to produce the observed power law spectrum of cosmic rays. One of the key elements of the DSA is the scattering of the cosmic rays by MHD turbulence, which is believed to exist both shock upstream and downstream. While the majority of past studies on the DSA adopt quasi-linear type model for the cosmic ray spatial diffusion, actual transport of the cosmic rays in a plasma with MHD turbulence can be qualitatively different. We studied the DSA process via test particle simulations by specifying non-Gaussian type scattering statistics to cosmic rays. The cosmic ray spectrum, spatial profile, and the acceleration time scale are evaluated, and are compared with observational data. In addition, fractal diffusion equation including the shock wave is numerically evaluated and the results are compared with the test particle simulations.