Laboratory Studies of Magnetorotational Instabilities in a Galium Disk

AST0205903古德曼类星体和X射线双星是天文天体的例子，它们通过将围绕黑洞运行的气体的引力能量转化为热量和辐射而发光。气体自身排列成一个以黑洞为中心的扁平圆盘。类似的圆盘围绕着年轻的恒星，形成行星。天体物理学家假设，这些圆盘的相邻环之间的湍流摩擦将这种轨道运动转化为热。大多数人认为，这种湍流是由一种磁不稳定性引起的，这种不稳定性除了在计算机模拟中之外，还没有在地球上复制出来。这种不稳定性需要高电导率的气体或液体，这一条件在太空和恒星中通常是满足的，但在地球上不是。空气、水和其他常见的流体是糟糕的导电体，而为核聚变研究创造的电离等离子体是良好的导体，但磁化强度太高。这个项目将在一个小型实验室实验中使用镓合金来研究天体物理不稳定性和湍流。镓是一种金属，在室温下是液体，比水粘度小，导电性比汞强，操作起来也更安全。这将被设置成在强磁场中同心圆柱体之间的快速旋转-这是一个动态类似于天体物理盘的系统。我们的目标是确认之前计算机对不稳定的预测，研究它对旋转、剪切和磁场强度的依赖，验证计算机模拟，也许还验证初始湍流。这些结果可能会证实我们对天体物理圆盘湍流的理解，而这还不能直接观察到。

AST 0205903GoodmanQuasars and X-ray binary stars are examples of astronomical objects that shine by converting the gravitational energy of gas orbiting a black hole into heat and radiation. The gas arranges itself into a flat disk centered on the black hole. Similar disks surround young stars and form planets. Astrophysicists postulate that turbulent friction between neighboring rings of these disks turns this orbital motion into heat. Most believe that this turbulence arises from a magnetic instability that has not yet been reproduced on earth except in computer simulations. The instability requires a gas or liquid of high electrical conductivity, a condition usually satisfied in space and in stars but not on earth. Air, water, and other common fluids are poor conductors of electricity while ionized plasmas created for fusion research are good conductors but too rigidly magnetized.This project will study astrophysical instability and turbulence in a small laboratory experiment using an alloy of gallium, a metal that is liquid at room temperature, less viscous than water, more conducting than mercury, and safer to handle. This will be set into rapid rotation between concentric cylinders in a strong magnetic field---a system dynamically similar to an astrophysical disk. The goals are to confirm previous computer predictions of the instability, to study its dependence on rotation, shear, and field strength, to validate computer simulations, and perhaps to demonstrate incipient turbulence. The results may confirm our understanding of astrophysical disk turbulence, which cannot yet be observed directly.***