3D simulations of turbulent mixing in a simplified slab-divertor geometry

•Simulations of turbulence have been conducted in the STORM module of BOUT  + + in a slab geometry mimicking the divertor leg of a tokamak.•Turbulence is driven by the Kelvin-Helmholtz mechanism due to radially sheared ExB flows close to the separatrix.•The turbulence forms a mixing layer around the separatrix which transports heat and particles into the private flux region.•An effective thermal diffusion coefficient of approximately 5.4 m2/s is measured, which corresponds to around 1/10th of the Bohm diffusion coefficient.•The diffusive approximation describes the evolution of the time and poloidally averaged profiles reasonably well as long as a suitable diffusion coefficient is chosen.