Inverse cascade in decaying three-dimensional magnetohydrodynamic turbulence.

We perform direct numerical simulations of three-dimensional freely decaying magnetohydrodynamic turbulence. For helical magnetic fields, an inverse cascade effect is observed in which power is transferred from smaller scales to larger scales. The magnetic field reaches a scaling regime with self-similar evolution, and power-law behavior at high wave numbers. We also find power-law decay in the magnetic and kinematic energies, and power-law growth in the characteristic length scale of the magnetic field.