Description
Complex dynamics of a broad range of astrophysical, industrial plasmas and magnetofluids are well
described by the magnetohydrodynamic(MHD) equations.
However, due to this inherent complexity, further assumptions are often required to gain results with available resources.
A common feature of many plasmas is a strong magnetic field. One approximation that uses this assumption is called Reduced MHD(RMHD). This
model is described as a nonlinear, low-frequency incompressible approximation to 3D compressible MHD.
It correctly illustrates many known features of the strong mean-field limit of
MHD, but clearly cannot capture the full picture. It is unclear exactly how the RMHD
assumptions affect the transport of energy across scales, which dynamical processes are fully and correctly described and which are neglected. To identify the physical processes governing
turbulent energy cascades that are retained in RMHD, we leverage an energy flux
decomposition, that has recently been extended from hydrodynamics to MHD. This technique provides
a clear framework to identify the processes present in 3D incompressible MHD turbulence by splitting
the energy flux into subfluxes that originate from vortex stretching, strain self-amplification, current-sheet
thinning or current-filament stretching, and to quantify their contribution to the energy cascade.
The equations for the
MHD fluxes are expanded using the RMHD approximation. Leading order terms help to identify the main
processes in RMHD which are likely to be accurately modelled at this order, while higher order terms allow
an insight into the importance of neglected terms. We discuss
results for both high- and low-beta plasmas.
