Description
The particle dynamics in plasmas has a highly multi-scale nature in terms of spatial scales, temporal scales, and energy range. In the solar wind, it spans about eight orders of magnitude in length (from fractions of the electron gyroradius to the Sun-Earth distance) and about five in energy. These ranges are way more extreme in astrophysical systems. Tackling the particle dynamics is thus a very challenging task, especially when the background plasma is highly turbulent.
We have developed an innovative approach, the multi-scale Box-in-Box (BIB), to model particle energisation in turbulent plasmas over a massive range of scales. First, we model the turbulent energy cascade from very large to very small scales coupling different models (MHD, hybrid, and fully kinetic), using a portion of a large simulation as initial condition for one with higher resolution multiple times in sequence. Then, we advance the trajectories of hundreds of millions of test particles on the evolving turbulent background from small to large scales while their gyroradius (and energy) increases. Our BIB approach allows for modelling the large-scale propagation of energetic particles in turbulent plasmas while retaining a realistic and self-consistent description of the microphysics responsible for particle energization. BIB simulations are key tools for developing new visualisation and analysis techniques for future multi-scale space missions such as NASA HelioSwarm and ESA Plasma Observatory.