  We report numerical simulations of surface gravity waves forced at small
scale and the subsequent inverse cascade of wave action. We combine the
spectral approach to simulating weakly nonlinear waves with the capabilities of
modern Graphics Processing Units to reach unprecedented scale separation
between the forcing and domain scales. The resulting broad inertial range
allows for an unambiguous confirmation of the theoretical prediction for the
spectrum in the inverse cascade regime, both in terms of spectral index and
dependence of the spectral level on the action flux.
