STEADY-STATE SOLUTIONS IN NONLINEAR DIFFUSIVE SHOCK ACCELERATION
STEADY-STATE SOLUTIONS IN NONLINEAR DIFFUSIVE SHOCK ACCELERATION
复制标题
非线性扩散冲击加速度的稳态解
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
P. Duffy
中科院分区：
文献类型：
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作者：
B. Reville;J. Kirk;P. Duffy
非线性扩散激波加速方程的定常解在宇宙线加速理论中起着基础性的作用。它们的存在通常需要允许一部分加速粒子从系统中逃逸出来。因为散射平均自由程被认为是能量的递增函数，所以这个条件通常被实现为能量空间的上限--一旦粒子的能量超过这个极限，它们就被允许从系统的任何部分逃逸。然而，由于加速粒子对激波前沿上游区域环境磁场的显著放大负责，我们研究了另一种粒子越过空间边界逃逸的方法。我们使用一个简单的迭代格式来构造耦合的动力学和流体动力学方程的定常数值解。对于适合于超新星遗迹的参数，当逃逸边界位于强驱动非共振波的增长和平流达到平衡的点时，我们找到了具有有效加速的定常解。我们还给出了分布函数在能量截止处附近的能量依赖关系--这是一个原则上可以观察到的诊断。
Stationary solutions to the equations of nonlinear diffusive shock acceleration play a fundamental role in the theory of cosmic-ray acceleration. Their existence usually requires that a fraction of the accelerated particles be allowed to escape from the system. Because the scattering mean free path is thought to be an increasing function of energy, this condition is conventionally implemented as an upper cutoff in energy space—particles are then permitted to escape from any part of the system, once their energy exceeds this limit. However, because accelerated particles are responsible for the substantial amplification of the ambient magnetic field in a region upstream of the shock front, we examine an alternative approach in which particles escape over a spatial boundary. We use a simple iterative scheme that constructs stationary numerical solutions to the coupled kinetic and hydrodynamic equations. For parameters appropriate for supernova remnants, we find stationary solutions with efficient acceleration when the escape boundary is placed at the point where growth and advection of strongly driven nonresonant waves are in balance. We also present the energy dependence of the distribution function close to the energy where it cuts off—a diagnostic that is in principle accessible to observation.