梯度漂移不稳定性是交叉场等离子体中旋转轮辐起源的直接证据
Direct evidence of the gradient drift instability being the origin of a rotating spoke in a crossed field plasma
摘要：
采用二维径向-方位角全动力学粒子蒙特卡罗碰撞（PIC/MCC）方法研究了交叉场放电中的等离子体旋转轮辐。动力学模型揭示了线性阶段梯度漂移不稳定性的整个扰动谱：Simon-Hoh，低杂波和离子声模式，提供了梯度漂移不稳定性本质的直接证据。利用梯度漂移不稳定性的双流体色散关系分析了不稳定性的线性发展。将电荷分离效应引入流体线性理论，采用超分辨信号处理方法（多重信号分类）获得数值频谱。模拟的频谱和增长率表现出良好的协议与理论色散关系（实频率和虚频率）在调查的情况下。最线性不稳定的模式被发现是低混合不稳定性和模式过渡到m=1宏观旋转结构后，饱和的线性相位是伴随着一个逆能量级联。在非线性阶段，当在轮辐前通道中引导的$\mathbf{E_θ\times B}$电子流的加热足以提供增强的电离时，可以发生显著的轮辐现象。
英文摘要：
A plasma rotating spoke in a crossed field discharge is studied using 2D radial-azimuthal fully kinetic Particle-In-Cell Monte Carlo Collision (PIC/MCC) simulations. The kinetic model reveals the whole perturbation spectrum of the gradient drift instability in the linear stage: Simon-Hoh, lower-hybrid and ion sound modes, providing direct evidence of the spoke of the gradient drift instability nature. The two-fluid dispersion relation of the gradient drift instability was utilized to analyze the linear development of instabilities in the simulations. The charge separation effect was incorporated in the fluid linear theory and a super-resolution signal processing method (multiple signal classification) was applied to obtain the numerical frequency spectrum. The simulated spectrum and growth rate show excellent agreement with the theoretical dispersion relation (real frequency and imaginary frequency) over investigated cases. The most linearly unstable mode was found to be the lower hybrid instability and the mode transition into the m=1 macroscopic rotating structure after saturation of the linear phase is accompanied by an inverse energy cascade. In the nonlinear stage, the pronounced spoke phenomena can occur when the heating of $\mathbf{E_θ\times B}$ electron flow channeled in the spoke front passage suffices to provide the enhanced ionization.
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