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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Cross-field diffusion of charged particles and the problem of ion injection and acceleration at quasi-perpendicular shocks
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Cross-field diffusion of charged particles and the problem of ion injection and acceleration at quasi-perpendicular shocks

机译：带电粒子的跨场扩散以及准垂直冲击下的离子注入和加速问题

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It is an open question how charged particles are injected at quasiperpendicular shocks into a first-order Fermi acceleration mechanism. Cross-field diffusion of solar wind ions is a possible injection process. However, in a system with at least one ignorable spatial dimension, charged particles moving in fluctuating fields are tied to the magnetic field lines. We have therefore determined the cross-field diffusion coefficient of charged particles in self-consistently generated turbulence by three-dimensional hybrid simulations. The initial setup consists of a homogeneous magnetic field with an isotropic core plasma plus a second, nongyrotropic ion distribution. The combined distributions resemble the distribution found immediately downstream of the quasi-perpendicular Earth bow shock: Part of the solar wind is transmitted (core) and part is specularly reflected and subsequently convected downstream (nongyrotropic part). Such a particle distribution excites the Alfven ion cyclotron and mirror mode instability. The turbulence scatters the nongyrotropic ions both parallel and perpendicular to the field. The perpendicular and the parallel diffusion coefficients have been determined for two values of the density of the nongyrotropic distributions, nb. The ratio of the two diffusion coefficients is smaller than the value predicted by hard sphere scattering theory, i.e., parallel scattering is considerably stronger than scattering perpendicular to the field. The power in the magnetic field fluctuations in the high nb case is comparable to the power obtained in a two-dimensional. quasiperpendicular shock simulation immediately behind the shock ramp. On the basis of perpendicular scattering time it is suggested that cross-field diffusion in the turbulent wave field generated by the specularly reflected ions is sufficient to inject and accelerate these ions effciently at quasi-perpendicular shocks. [References: 24]
机译：这是一个悬而未决的问题，如何将带电粒子在准七边形激波下注入一阶费米加速机制。太阳风离子的跨场扩散是可能的注入过程。然而，在具有至少一个可忽略的空间尺寸的系统中，在波动场中移动的带电粒子被束缚在磁场线上。因此，我们通过三维混合仿真确定了自洽产生的湍流中带电粒子的跨场扩散系数。初始设置包括具有各向同性核心等离子体的均匀磁场以及第二非促旋离子分布。组合的分布类似于准垂直地球弓激波下游的分布：一部分太阳风被传输（核心），一部分被镜面反射，随后被对流向下游（非旋回部分）。这种粒子分布激发了Alfven离子回旋加速器和镜模不稳定性。湍流使非回旋离子平行于场垂直散射。已经确定了非回旋分布密度的两个值nb的垂直和平行扩散系数。两个扩散系数之比小于硬球散射理论预测的值，即平行散射比垂直于场的散射要强得多。在高nb情况下磁场波动中的功率可与二维获得的功率相当。在冲击坡道后面立即进行准四边形冲击仿真。根据垂直散射时间，建议由镜面反射离子产生的湍流场中的跨场扩散足以在准垂直冲击下有效注入和加速这些离子。 [参考：24]

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