Separation of Magnetic Field Lines in Transverse 3D Turbulence Using the Random Ballistic Decorrelation

The interplanetary magnetic field is turbulent, and its field lines follow a random walk that becomes diffusive beyond a correlation scale. The field line random walk (FLRW) strongly influences the transport of energetic charged particles. While the FLRW determines how far a field line can wander, the separation of magnetic field lines determines how a bundle of field lines spread out into space, along with a distribution of energetic charged particles, such as solar energetic particles. In this work, we study the separation of two magnetic field lines subject to transverse turbulent magnetic fluctuations. We assume Corrsin's hypothesis and random ballistic decorrelation and derive the diffusion coefficient for the separation of two field lines for different types of turbulence. We verify our analytic results with computer simulations. Partially supported by grant RTA6280002 from Thailand Science Research and Innovation.