论文标题
基于周期势场的相对磁性螺旋性
Relative Magnetic Helicity Based on a Periodic Potential Field
论文作者
论文摘要
磁性螺旋度在理想的磁流失动力学（MHD）下是保守的，即使在电阻过程中也是准持有的。磁性螺旋度的标准定义不能直接应用于体积中的开放磁场，因为它依赖于仪表。相反，相对磁性螺旋度被广泛使用。我们发现，具有周期性横向边界条件的矩形结构域中电势磁场的能量小于所有六个边界上固定正常分量的场的能量。为了在分析相对磁性螺旋度的分析中使用这种较低的能量场，我们引入了磁场的磁性螺旋性的新定义，该定义涉及周期电位场。我们将此定义应用于一系列分析解决方案和数值模拟。结果表明，我们的新规格不变的螺旋性非常接近原始磁场的相对磁性螺旋的电流携带部分。我们还发现，携带电流的螺旋与原始和我们定义的相对螺旋性的相对磁性螺旋性之间的比率不同。由于体积中的电流，新的螺旋性似乎对场的组成部分更敏感，这是不稳定性和太阳喷发现象的来源。
Magnetic helicity is conserved under ideal magnetohydrodynamics (MHD) and quasi-conserved even under a resistive process. The standard definition for magnetic helicity cannot be applied directly to an open magnetic field in a volume, because it is gauge-dependent. Instead, the relative magnetic helicity is widely used. We find that the energy of a potential magnetic field in a rectangular domain with periodic lateral boundary conditions is less than that of the field with a fixed normal component on all six boundaries. To make use of this lower energy potential field in the analysis of relative magnetic helicity, we introducing a new definition for magnetic helicity for the magnetic field, which involves the periodic potential field. We apply this definition to a sequence of analytic solutions and a numerical simulation. The results show that our new gauge-invariant helicity is very close to the current-carrying part of the relative magnetic helicity of the original magnetic field. We find also that the ratio between the current-carrying helicity and the relative magnetic helicity for the original and our defined relative helicity show different behavior. It seems that the new helicity is more sensitive to the component of the field due to the electric current in the volume, which is the source for instabilities and solar eruptive phenomena.
