  We show that Kerr beam self-cleaning results from parametric mode mixing
instabilities, that generate a number of nonlinearly interacting modes with
randomized phases -- optical wave turbulence, followed by a direct and inverse
cascade towards high mode numbers and condensation into the fundamental mode,
respectively. This optical self-organization effect is analogue to wave
condensation that is well-known in hydrodynamic 2D turbulence.
