各向异性等离子体中撕裂模不稳定性和磁场重联的数值研究

NUMERICAL STUDIES OF TEARING MODE INSTABILITY AND MAGNETIC RECONNECTION IN ANISOTROPIC PLASMA

应用二维三分量时变可压缩磁流体动力学模拟方法 ,数值研究了各向异性等离子体 (P⊥ ≠P∥ ,T⊥ ≠T∥)中的撕裂模不稳定性和磁场重联过程 .计算结果表明 ,在短暂的线性增长之后 ,不稳定性将趋于非线性饱和 .线性增长率随着各向异性程度 |P⊥/P∥|增强而增大 ,随着等离子体 β值减小及磁场y分量By 增大而降低 .在强垂直各向异性 (P⊥ >P∥)的情况下 ,电流片中磁场重联形成的磁岛达到非线性饱和后 ,在X型点附近形成空腔结构 ;随着空腔的增大 ,磁岛逐渐变小 ,并最终消失 .在P⊥ >P∥ 情况下 ,仅在电流片中心区域可以激发火蛇管不稳定性 。

The tearing mode instability and magnetic reconnection process in an anisotropic plasma ( P ⊥≠P ∥ , T ⊥≠T ∥ ) are numerically studied by a two dimensional three component time dependant compressible MHD simulation. It is found that the instability tends to become nonlinear saturation after, a short period of linear growth. The growth rate will increase when the intensity of pressure anisotropy P ⊥/P ∥ increases, while it will decrease with the decrease of the plasma β and the augment in the y component B y of magnetic field. In case of a large perpendicular anisotropy ( P ⊥>P ∥ ), when the magnetic island formed in the current sheet by magnetic reconnection becomes nonlinear saturation, there will be cavity structures formed near the X points. The cavities become larger gradually while the magnetic islands become smaller and vanish at last. In the plasma with a parallel anisotropy ( P ⊥<P ∥ ), the fire hose instability can only be excited in the central region of current sheet, and large magnetic island can't be formed in the current sheet. [