Diffusive shock re-acceleration
Diffusive shock re-acceleration
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DOI：
10.1017/s0022377818000478
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发表时间：
2018-06-01
影响因子：
2.5
通讯作者：
Spitkovsky, Anatoly
中科院分区：
文献类型：
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作者：
Caprioli, Damiano;Zhang, Horace;Spitkovsky, Anatoly
我们已经进行了二维混合模拟的非相对论性碰撞无冲击的存在下预先存在的高能粒子（“种子”），这样的研究适用于，例如，银河宇宙射线（CR）的超新星遗迹（SNR）的冲击和太阳风高能粒子在日光层冲击的再加速。高能粒子可以被有效地反射和加速，而不管冲击波的倾斜，通过一个过程，我们称之为扩散冲击再加速。我们发现，再加速种子可以驱动上游的冲击流不稳定性，并产生有效的磁场放大。这最终可以触发热质子的注入，即使在通常不能注入热粒子的斜激波。我们的特点，在反射种子的电流，发现它往往是一个通用的值J类似或等于en（CR）v（SH），其中en（CR）是种子电荷密度和V-SH是冲击速度。当我们的研究结果应用到信噪比，我们发现，银河CRs的再加速可以激发贝尔不稳定性的非线性水平在不到10年，从而提供了一个最低水平的磁场放大任何SNR冲击。最后，我们讨论了扩散激波再加速的相关性，也为其他环境，如日光层的冲击，银河超级气泡和星系团。
We have performed two-dimensional hybrid simulations of non-relativistic collisionless shocks in the presence of pre-existing energetic particles ('seeds'); such a study applies, for instance, to the re-acceleration of galactic cosmic rays (CRs) in supernova remnant (SNR) shocks and solar wind energetic particles in heliospheric shocks. Energetic particles can be effectively reflected and accelerated regardless of shock inclination via a process that we call diffusive shock re-acceleration. We find that re-accelerated seeds can drive the streaming instability in the shock upstream and produce effective magnetic field amplification. This can eventually trigger the injection of thermal protons even at oblique shocks that ordinarily cannot inject thermal particles. We characterize the current in reflected seeds, finding that it tends to a universal value J similar or equal to en(CR)v(sh), where en(CR) is the seed charge density and V-sh is the shock velocity. When applying our results to SNRs, we find that the re-acceleration of galactic CRs can excite the Bell instability to nonlinear levels in less than similar to 10 yr, thereby providing a minimum level of magnetic field amplification for any SNR shock. Finally, we discuss the relevance of diffusive shock re-acceleration also for other environments, such as heliospheric shocks, galactic superbubbles and clusters of galaxies.