磁场放大非线性扩散冲击波加速中的Turbulence耗散和粒子注入
Turbulence Dissipation and Particle Injection in Non-Linear Diffusive Shock Acceleration with Magnetic Field Amplification
摘要:
对超新星遗迹(SNR)壳层的观测表明,高度放大的磁场很可能是激波有效加速粒子的固有部分。这种强烈的湍流,这可能是由于宇宙射线驱动的不稳定性,共振和非共振,在冲击前兆,是一定要发挥关键作用的自洽,非线性模型的强,宇宙射线修改冲击。在这里,我们提出了一个Monte Carlo模型的非线性扩散冲击加速(DSA)占磁场放大通过共振不稳定性引起的加速粒子,并包括上游的冲击和随后的前体等离子体加热的湍流耗散的影响。由于湍流耗散和粒子注入等离子体加热之间的反馈效应很强,增加了有效DSA的非线性性质。描述的湍流阻尼的参数化的方式,我们得到两个重要的结果:第一,典型的超新星遗迹冲击的条件下,即使是少量的耗散湍流能量(~10%)是足够的显着加热的前体等离子体,第二,加热上游的冲击导致增加的热粒子在亚激波的注入的几个因素。在我们的研究结果中,非线性激波结构对粒子注入的增强的响应阻止了粒子加速和磁场放大的效率增加。然而,我们认为,更先进的(可能是非共振)模型的湍流产生和耗散可能会导致一种情况下,由于湍流耗散的粒子注入升压的结果在更有效的加速和更强的放大磁场比没有耗散。
英文摘要:
The highly amplified magnetic fields suggested by observations of some supernova remnant (SNR) shells are most likely an intrinsic part of efficient particle acceleration by shocks. This strong turbulence, which may result from cosmic ray driven instabilities, both resonant and non-resonant, in the shock precursor, is certain to play a critical role in self-consistent, nonlinear models of strong, cosmic ray modified shocks. Here we present a Monte Carlo model of nonlinear diffusive shock acceleration (DSA) accounting for magnetic field amplification through resonant instabilities induced by accelerated particles, and including the effects of dissipation of turbulence upstream of a shock and the subsequent precursor plasma heating. Feedback effects between the plasma heating due to turbulence dissipation and particle injection are strong, adding to the nonlinear nature of efficient DSA. Describing the turbulence damping in a parameterized way, we reach two important results: first, for conditions typical of supernova remnant shocks, even a small amount of dissipated turbulence energy (~10%) is sufficient to significantly heat the precursor plasma, and second, the heating upstream of the shock leads to an increase in the injection of thermal particles at the subshock by a factor of several. In our results, the response of the non-linear shock structure to the boost in particle injection prevented the efficiency of particle acceleration and magnetic field amplification from increasing. We argue, however, that more advanced (possibly, non-resonant) models of turbulence generation and dissipation may lead to a scenario in which particle injection boost due to turbulence dissipation results in more efficient acceleration and even stronger amplified magnetic fields than without the dissipation.
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