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Magnetorotational and Magnetic Buoyancy Instabilities in Differentially Rotating Disks

差动旋转盘中的磁旋转和磁浮力不稳定性

基本信息

批准号：
07640348
负责人：
MATSUMOTO Ryoji
金额：
$ 1.47万
依托单位：
Chiba University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1997
项目状态：
已结题

项目摘要

1.By means of three-dimensional local magnetohydrodynamic (MHD) simulations, we studied the nonlinear evolution of magnetorotational instabilities and magnetic buoyancy instabilities in gravitationa11y stratified, differentially rotating disks. We found that magnetic accretion disks have two states ; a gas pressure dominated quasi-steady state and a magnetic pressure dominated state. In the latter state, buoyancy driven magnetic field amplification occurs.2.We carried out global MHD simulations of differentially rotating torus threaded by large scale vertical magnetic fields and studied the dependence of jet speed and mass outflow rates on the magnetic field strength. By 3D MHD simulations, we showed that the growth of non-axisymmetric instabilities in the torus also create non-axisymmetric structures inside the jet.3.We studied the time evolution of a torus threaded by weak toroidal magnetic fields. The amplification of magnetic fields inside the torus saturates after 10 rotation period when magnetic turbulence develops. The ratio of the gas pressure to magnetic pressure in the torus is about 10 in this state. Because of the effcient angular momentum transport, the angular momentum distribution approaches to the Keplerian rotation. The effective value of the angular momentum transport rate, alpha, is between 0.01 and 0.1. We also found that filamentary magnetic pressure dominated regions appear and that magnetic loops rise buoyantly.4.We carried out axisymmetric 2D simulations of the interaction between the dipole magnetic field of the central star and surrounding accretion disks. The magnetic helicity injected from the disk drives magnetic reconnection and ejection of hot plasmoids. We applied this mechanism to X-ray flares and optical jets observed in protostars.5.We wrote parallelized MHD codes for various parallel computers and confirmed that the efficiency of the code is almost proportional to the number of processing elements.

1.利用三维局域磁流体力学(MHD)模拟方法，研究了重力层状差分旋转圆盘中磁致旋转不稳定性和磁浮力不稳定性的非线性演化。我们发现，磁吸积盘有两种状态：气体压力主导的准稳态和磁压主导的准稳态。2.对大尺度垂直磁场作用下的差动旋转圆环进行了整体MHD模拟，研究了射流速度和质量流出速率随磁场强度的变化规律。通过三维MHD模拟，我们发现环面中非轴对称不稳定性的增长也在射流内部形成了非轴对称结构。3.研究了环面在弱磁场作用下的时间演化。在磁湍流发展的10个旋转周期后，环面内磁场的放大达到饱和。在这种状态下，环面内的气体压力与磁场压力之比约为10。由于有效的角动量输运，角动量分布接近于开普勒式旋转。角动量输运率的有效值α介于0.01和0.1之间。我们还发现出现了丝状磁压占主导地位的区域，磁环上升得很快。4.我们对中心星偶极磁场与周围吸积盘之间的相互作用进行了轴对称的2D模拟。从磁盘注入的磁螺旋度驱动热等离子体磁重联和弹射。我们将这一机制应用于观测到的X射线耀斑和光学喷流。5.我们为各种并行计算机编写了并行化的MHD程序，并证实了该程序的效率几乎与处理单元的数量成正比。