Stochasticity of magnetic field lines is paramount to understanding particle transport and mixing (Rechester and Rosenbluth 1978 Phys. Rev. Lett. 40 38-41). In this paper we study magnetic field separation in turbulent plasmas, which feature so-called superdiffusion, where field lines separate faster than diffusively. We discovered that turbulent superdiffusion can be pronouncedly asymmetric, so that the separation of field lines will be different if one follows magnetic field lines along the direction of the field or follows them in the opposite direction. Particle transport perpendicular to the magnetic field is primarily due to the field line separation in collisionless, well-magnetized plasmas. The asymmetry in diffusion, however, was certainly unexpected, as it will create free energy in particles that follow field lines, e. g. it will create large-scale streaming out of particle gradients perpendicular to the mean magnetic field. While the symmetry of the flow is broken by the so-called imbalance or cross-helicity, the difference between forward and backward diffusion is not directly due to imbalance, but a non-trivial consequence of both imbalance and non-reversibility of turbulence. It therefore follows that this peculiar property of field lines is directly related to turbulence being a dissipative phenomenon, and that turbulence can directly channel part of its free energy to particles.
展开▼
机译：磁场线的随机性对于理解粒子的传输和混合至关重要（Rechester and Rosenbluth 1978 Phys。Rev. Lett。40 38-41）。在本文中，我们研究了湍流等离子体中的磁场分离，这种磁场具有所谓的超级扩散，其中场线的分离速度比扩散速度快。我们发现湍流超级扩散可以明显地是不对称的，因此，如果沿着磁场方向跟随磁场线或沿着相反方向遵循磁场线，则磁场线的分离将是不同的。垂直于磁场的粒子传输主要是由于无碰撞的，磁化强度好的等离子体中的磁力线分开。然而，扩散的不对称性肯定是出乎意料的，因为它将在遵循电场线的粒子中产生自由能。 G。它会从垂直于平均磁场的粒子梯度中产生大规模流。尽管流动的对称性被所谓的不平衡或交叉螺旋破坏，但向前和向后扩散之间的差异不是直接由于不平衡引起的，而是由不平衡和湍流不可逆性造成的非同寻常的结果。因此，由此得出的结论是，场线的这种特殊性质与湍流是一种耗散现象直接相关，并且湍流可以将其自由能的一部分直接引导到粒子上。
展开▼
