Energetic particle parallel diffusion in a cascading wave turbulence in the foreshock region
Energetic particle parallel diffusion in a cascading wave turbulence in the foreshock region
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DOI：
10.5194/npg-14-587-2007
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发表时间：
2007-09
影响因子：
2.2
通讯作者：
F. Otsuka;Y. Omura;O. Verkhoglyadova
中科院分区：
文献类型：
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作者：
F. Otsuka;Y. Omura;O. Verkhoglyadova
通过实验粒子模拟，研究了高能粒子在弓形激波上游的平行（场向）扩散。我们假设弓形激波的平行激波几何形状，并且在恒定背景磁场的一维系统中，由太阳风向激波方向对流的MHD波湍流纯粹是横向的。我们使用了三种湍流模型：均匀湍流，从大尺度到小尺度的规则级联，以及从小尺度到大尺度的逆级联。对于均匀模型，粒子沿平均场的运动是布朗运动，这是由于沿90度俯仰角的随机散射和各向同性散射。另一方面，由于有限时间尺度的相干和各向异性俯仰角散射，两种级联模型的粒子运动是非布朗运动。由这些粒子运动的系综平均计算的平均自由程k显示出与激波的距离有关。它还取决于粒子的热速度、太阳风流速和波浪湍流模型等参数。对于逆级联模型，激波处k对热能的依赖性与Giacalone（2004）的混合模拟一致，但k的空间依赖性与之不一致。
We study parallel (field-aligned) diffusion of en- ergetic particles in the upstream of the bow shock with test particle simulations. We assume parallel shock geometry of the bow shock, and that MHD wave turbulence convected by the solar wind toward the shock is purely transverse in one-dimensional system with a constant background mag- netic field. We use three turbulence models: a homogeneous turbulence, a regular cascade from a large scale to smaller scales, and an inverse cascade from a small scale to larger scales. For the homogeneous model the particle motions along the average field are Brownian motions due to ran- dom and isotropic scattering across 90 degree pitch angle. On the other hand, for the two cascade models particle mo- tion is non-Brownian due to coherent and anisotropic pitch angle scattering for finite time scale. The mean free path k calculated by the ensemble average of these particle motions exhibits dependence on the distance from the shock. It also depends on the parameters such as the thermal velocity of the particles, solar wind flow velocity, and a wave turbulence model. For the inverse cascade model, the dependence of k at the shock on the thermal energy is consistent with the hybrid simulation done by Giacalone (2004), but the spatial dependence of k is inconsistent with it.