  Results of a three-dimensional, flux-driven, electrostatic, global, two-fluid
turbulence simulation for a 5-field period stellarator with an island divertor
are presented. The numerical simulation is carried out with the GBS code,
recently extended to simulate plasma turbulence in non-axisymmetric magnetic
equilibria. The vacuum magnetic field used in the simulation is generated with
the theory of Dommaschk potentials, and describes a configuration with a
central region of nested flux surfaces, surrounded by a chain of magnetic
islands, similarly to the diverted configurations of W7-X. The heat outflowing
from the core reaches the island region and is transported along the magnetic
islands, striking the vessel walls, which correspond to the boundary of the
simulation domain.
  The radial transport of particles and heat is found to be mainly driven by a
field-aligned coherent mode with poloidal number $m=4$. The analysis of this
mode, based on non-local linear theory considerations, shows its ballooning
nature. In contrast to tokamak simulations and experiments, where blobs often
contribute to transport, we do not observe the presence of intermittent
transport events.
