  In space and astrophysical plasmas, violent events or instabilities inject
energy into turbulent motions at large scales. Nonlinear interactions among the
turbulent fluctuations drive a cascade of energy to small perpendicular scales
at which the energy is ultimately converted into plasma heat. Previous work
with the incompressible magnetohydrodynamic (MHD) equations has shown that this
turbulent energy cascade is driven by the nonlinear interaction between
counterpropagating Alfven waves - also known as Alfven wave collisions. Direct
numerical simulations of weakly collisional plasma turbulence enables deeper
insight into the nature of the nonlinear interactions underlying the turbulent
cascade of energy. In this paper, we directly compare four cases: both periodic
and localized Alfven wave collisions in the weakly and strongly nonlinear
limits. Our results reveal that in the more realistic case of localized Alfven
wave collisions (rather than the periodic case), all nonlinearly generated
fluctuations are Alfven waves, which mediates nonlinear energy transfer to
smaller perpendicular scales.
