We present results of a two-dimensional fully kinetic particle-in-cell simulation in order to shed light on the role of whistler waves in the scattering of strahl electrons and in the heat-flux regulation in the solar wind. We model the electron velocity distribution function as initially composed of core and strahl populations as typically encountered in the near-Sun solar wind as observed by Parker Solar Probe. We demonstrate that, as a consequence of the evolution of the electron velocity distribution function (VDF), two branches of the whistler heat-flux instability can be excited, which can drive whistler waves propagating in the direction oblique or parallel to the background magnetic field. First, oblique whistler waves induce pitch-angle scattering of strahl electrons, toward higher perpendicular velocities. This leads to the broadening of the strahl pitch-angle distribution and hence to the formation of a halo-like population at the expense of the strahl. Later on, the electron VDF experiences the effect of parallel whistler waves, which contributes to the redistribution of the particles scattered in the perpendicular direction into a more symmetric halo, in agreement with observations. Simulation results show a remarkable agreement with the linear theory of the oblique whistler heat-flux instability. The process is accompanied by a significant decrease of the heat flux carried by the strahl population.

我们展示了二维全动力学粒子细胞内模拟的结果，以阐明惠斯勒波在斯特拉尔电子散射和太阳风热通量调节中的作用。我们将电子速度分布函数建模为最初由核心和斯特拉尔种群组成，如帕克太阳探测器观察到的近太阳太阳风中通常遇到的那样。我们证明，由于电子速度分布函数（VDF）的演变，可以激发惠斯勒热通量不稳定性的两个分支，这可以驱动惠斯勒波在与背景磁场倾斜或平行的方向上传播. 首先，倾斜的哨声波引起斯特拉尔电子的俯仰角散射，朝向更高的垂直速度。这导致斯特拉尔螺距角分布的加宽，从而导致以斯特拉尔为代价的晕状种群的形成。稍后，电子 VDF 会经历平行的哨声波的影响，这有助于将垂直方向散射的粒子重新分布成更对称的光晕，与观察结果一致。模拟结果表明与斜口哨热通量不稳定性的线性理论具有显着的一致性。该过程伴随着斯特拉尔种群携带的热通量的显着降低。这有助于将垂直方向散射的粒子重新分布成更对称的光晕，与观察结果一致。模拟结果表明与斜口哨热通量不稳定性的线性理论具有显着的一致性。该过程伴随着斯特拉尔种群携带的热通量的显着降低。这有助于将垂直方向散射的粒子重新分布成更对称的光晕，与观察结果一致。模拟结果表明与斜口哨热通量不稳定性的线性理论具有显着的一致性。该过程伴随着斯特拉尔种群携带的热通量的显着降低。