Laboratory Studies of Magnetorotational Instabilities in a Galium Disk

类星体和x射线双星是通过将围绕黑洞运行的气体的引力能转化为热和辐射而发光的天体的例子。这些气体以黑洞为中心排列成一个扁平的圆盘。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，这些圆盘邻近环之间的湍流摩擦将这种轨道运动转化为热量。大多数人认为，这种湍流是由磁场的不稳定性引起的，这种不稳定性除了在计算机模拟中还没有在地球上重现。这种不稳定性需要高导电性的气体或液体，这种条件通常在太空和恒星中满足，但在地球上却不满足。空气、水和其他常见的液体是电的不良导体，而为核聚变研究创造的电离等离子体是良导体，但磁化太强。该项目将在一个小型实验室中使用镓合金研究天体物理的不稳定性和湍流。镓合金是一种在室温下呈液态的金属，比水的粘性小，比汞的导电性强，而且处理起来更安全。这将被设置成在强磁场中的同心圆柱体之间快速旋转——一个动态类似于天体物理磁盘的系统。目的是证实先前的计算机对不稳定性的预测，研究其对旋转、剪切和场强的依赖，验证计算机模拟，并可能证明早期的湍流。这些结果可能会证实我们对天体物理盘湍流的理解，这是目前还不能直接观察到的

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.***