PIC SIMULATIONS OF THE EFFECT OF VELOCITY SPACE INSTABILITIES ON ELECTRON VISCOSITY AND THERMAL CONDUCTION
PIC SIMULATIONS OF THE EFFECT OF VELOCITY SPACE INSTABILITIES ON ELECTRON VISCOSITY AND THERMAL CONDUCTION
复制标题
DOI：
10.3847/0004-637x/824/2/123
复制
发表时间：
2016-02
期刊：
影响因子：
--
通讯作者：
M. Riquelme;E. Quataert;D. Verscharen
中科院分区：
文献类型：
--
作者：
M. Riquelme;E. Quataert;D. Verscharen
在低碰撞等离子体中，速度-空间不稳定性是为等离子体提供有效碰撞的关键机制。我们使用粒子单元(PIC)模拟来研究电子和离子尺度的速度空间不稳定性之间的相互作用及其对电子压力各向异性、粘性加热和热传导的影响。低碰撞等离子体中磁矩的绝热不变性导致压力各向异性，如果磁场被放大(表示垂直和平行于的j种(电子、离子)的压力)。如果产生的各向异性足够大，它反过来会引发小规模的等离子体不稳定性。我们的PIC模拟通过在等离子体中施加剪切来连续放大磁场，探索了镜面、IC和电子哨声不稳定性的非线性区域。在()区中，饱和电子压强各向异性主要由(电子长尺度)哨声边缘稳定条件决定，由于电子被离子长尺度反射镜俘获，∼约减小1.5-2倍。我们显式地计算了电子和离子沿平均磁场的平均自由程，并给出了低碰撞βj≳1等离子体的平均自由程和热导率的简单物理描述。我们的结果表明，速度-空间不稳定性可能会降低大质量、热的星系团外部等离子体的热导率。我们还讨论了我们的结果对低碰撞吸积流到黑洞的电子加热和热传导的影响，包括银河系中心的SgrA*。
In low-collisionality plasmas, velocity-space instabilities are a key mechanism providing an effective collisionality for the plasma. We use particle-in-cell (PIC) simulations to study the interplay between electron- and ion-scale velocity-space instabilities and their effect on electron pressure anisotropy, viscous heating, and thermal conduction. The adiabatic invariance of the magnetic moment in low-collisionality plasmas leads to pressure anisotropy, , if the magnetic field is amplified ( and denote the pressure of species j (electron, ion) perpendicular and parallel to ). If the resulting anisotropy is large enough, it can in turn trigger small-scale plasma instabilities. Our PIC simulations explore the nonlinear regime of the mirror, IC, and electron whistler instabilities, through continuous amplification of the magnetic field by an imposed shear in the plasma. In the regime ( ), the saturated electron pressure anisotropy, , is determined mainly by the (electron-lengthscale) whistler marginal stability condition, with a modest factor of ∼1.5–2 decrease due to the trapping of electrons into ion-lengthscale mirrors. We explicitly calculate the mean free path of the electrons and ions along the mean magnetic field and provide a simple physical prescription for the mean free path and thermal conductivity in low-collisionality βj ≳ 1 plasmas. Our results imply that velocity-space instabilities likely decrease the thermal conductivity of plasma in the outer parts of massive, hot, galaxy clusters. We also discuss the implications of our results for electron heating and thermal conduction in low-collisionality accretion flows onto black holes, including Sgr A* in the Galactic Center.