Decoupling of the Kinetic and Magnetic Energy Cascades in MHD Turbulence
  Magnetic and kinetic energy in ideal incompressible MHD are not global
invariants and, therefore, it had been justified to discuss only the cascade of
their sum, total energy. We provide a physical argument based on scale-locality
of the cascade, along with compelling evidence that at high Reynolds numbers,
magnetic and kinetic energy budgets statistically decouple beyond a
transitional "conversion" range. This arises because magnetic field-line
stretching is a large-scale process which vanishes on average at intermediate
and small scales within the inertial-inductive range, thereby allowing each of
mean kinetic and magnetic energy to cascade conservatively and at an equal
rate. One consequence is that the turbulent magnetic Prandtl number is unity
over the "decoupled range" of scales.
