Development of a Magnetostrophic Geodynamo

发电机是一种将机械能转化为电能的装置。它通过在磁场中移动电导体来实现这一点。这会产生电流，而电流又会产生自己的感应磁场。当感应磁场和感应磁场相同时，发电机变为自激。一个类似的自激过程产生了地球磁场。相关的电流在地核中流动，地核是半径为2200英里的近乎球形的液态铁，环绕地球中心。由于这种导电流体的运动，地球的核心是一个巨大的发电机，被称为“地球发电机”。发电机还需要一个电源来维持其运动和电力生产，尽管通过电阻造成热损失。对于地球发电机来说，动力来源被认为是由于核心密度差异的浮力。功率不仅用于维持磁场，而且用于克服与流体运动相反的摩擦力。目前的数值模拟假设摩擦能损失与电阻损失相当，但人们普遍认为，现实中摩擦能损失要小得多。忽略摩擦损失的发电机被称为磁转，研究人员最近重新唤起了等离子体物理学家布莱恩·泰勒的旧想法，这让他们采用了一种新的数值方法，通过这种方法，他们已经推导出了磁转方程的二维解。研究人员相信，当他们将解变成三维的(一个复杂的步骤)时，它们将成为未来磁场创造模拟的新范例，并导致更好地理解地球和其他行星是如何产生磁力的。磁罗盘指针的寻北特性表明，科里奥利力强烈影响地心运动。这种力主要由浮力和洛伦兹力来平衡，洛伦兹力是磁场施加在载流导体上的力。泰勒在1953年展示了如何实现简化的动态平衡，从而确定了流体速度是磁场的泛函。要使回热回路闭合，必须根据流体速度确定磁场，但这是众所周知的、众所周知的运动学发电机过程。在1953年，未来的道路似乎很简单，但自那以来所有坚定的尝试都失败了，在今年调查小组之前。通过假设相对于地球自转轴的对称性，该模型大大简化了。著名的阿尔法效应被用作动力源。这也使得原本可以排除轴对称解的考林定理不再适用。为了让发电机社区相信这一成功是有意义的，该团队计划放弃轴对称，消除阿尔法效应，并依靠浮力提供所需的动力。研究人员认为，他们的结果将让发电机群体大开眼界，并将成为行星和恒星中自然产生的发电机模型的基础，这些模型比今天的模拟更真实，因为目前的模拟假设粘性摩擦太大。

A dynamo is a device that converts mechanical energy into electrical energy. It does this by moving an electrical conductor across a magnetic field. This induces an electrical current which creates its own induced magnetic field. The dynamo becomes self-excited when the induced and inducing magnetic fields are the same. A similar self-excited process creates Earth's magnetic field. The associated electric currents flow in the Earth's core, a nearly spherical mass of liquid iron, of radius 2,200 miles, surrounding the Earth's center. Because of this conducting fluid's motion, the Earth's core is a gigantic electric generator, called 'the geodynamo'. A dynamo also needs a power source to maintain its motion and production of electricity despite heat losses through electrical resistance. For the geodynamo the power source is thought to be due to the buoyancy of density differences in the core. The power is expended not only in maintaining the magnetic field but also in overcoming the frictional forces opposing the fluid motion. Current numerical simulations assume that the frictional energy losses are comparable with those from electrical resistance, but it is generally agreed that in reality they are very much less. A dynamo that ignores frictional losses is termed magnetostrophic, and the investigators have recently revived an old idea of the plasma physicist, Bryan Taylor, that has led them to a new numerical procedure through which they have already derived two-dimensional solutions of the magnetostrophic equations. The investigators believe that, when they have made the solutions three-dimensional (a complicated step), they will become the new paradigm for future simulations of magnetic field creation and lead to a better understanding of how the Earth and other planets create their magnetism.The north-seeking property of the magnetic compass needle shows that the Coriolis force strongly influences core motion. This force is balanced primarily by buoyancy and the Lorentz force, which is the force exerted on a current-carrying conductor by the magnetic field. Taylor showed in 1953 how the resulting simplified dynamical balance could be achieved, so determining the fluid velocity as a functional of the magnetic field. To close the regenerative loop, it is necessary to determine the magnetic field from the fluid velocity, but that is the well-known and well-understood kinematic dynamo process. The way ahead seemed simple in 1953 but all the determined attempts made since then to implement Taylor's suggestion failed, prior to that of the investigating team this year. The model was greatly simplified by assuming symmetry with respect to the Earth's rotation axis. The well-known alpha-effect was invoked as the power source. This also made Cowling's theorem, that otherwise would have ruled out axisymmetric solutions, inapplicable. To convince the dynamo community that this success is meaningful, the team plans to abandon axisymmetry, remove the alpha-effect, and rely on buoyancy to supply the required power. The investigators believe that their results will be an eye-opener for the dynamo community, and will become the basis for models of naturally-occurring dynamos in planets and stars that are more realistic than today's simulations which assume a viscous friction that is very much too large.