各向异性等离子体多重电流片的演化

应用二维三分量磁流体动力学方程组模拟,数值研究了压力各向异性等离子体周期多重电流片的演化.发现在β<<1时,微弱的各向异性仅仅使电流片中磁场重联的速度加快.而当β≈1(即热压与磁压相当时),微弱的垂直各向异性(P_┴>P_//)不仅大大加速了磁场重联的速度,还使重联位置发生显著变化.初始反对称的磁场重联位形逐步转化为对称的磁场位形,进而再演化为与初始反相的反对称磁场位形.场向各向异性(P_┴<P_//)和强的垂直各向异性都导致不稳定性增长率成倍增加.但在场向各向异性下磁场位形基本不变,只在电流片中心出现不规则扰动.同样参数下各向异性等离子体多重电流片中磁场重联形成的磁岛比各向同性多层电流片要小.

THE EVOLUTION OF MULTIPLE CURRENT SHEET IN ANISOTROPIC PLASMA

The evolution of periodic multiple current sheets in the presence of a pressure anisotropy is numerically simulated based on a two-dimensional three component magnetohydrodynamic method. It is found out that when the plasma parameter β<<1, a slight anisotropy can only expedite the magnetic reconnection process. When the plasma parameter β≈1 （means that the thermal pressure is comparable with the magnetic pressure）, slight perpendicular anisotropy can not only expedite the magnetic reconnection process, but also change the position of X line in reconnection. The magnetic filed changes gradually from an anti-symmetric configuration to a symmetric shape, which will further evolve into an anti-symmetric configuration in opposite phase with initial configuration. Large perpendicular anisotropy or parallel anisotropy will enhance the growth rate dramatically. But the magnetic field configuration does not have fundamental change in parallel anisotropy. There are only some irregular disturbs in the center of the current sheet. The magnetic islands that formed in the anisotropy plasma with periodical current sheets are smaller than those formed in isotropic periodical current sheets with same parameters.