  Small-angle neutron scattering is used in combination with transport
measurements to investigate the current-induced effects on the morphology of
the intermediate mixed state domains in the intertype superconductor niobium.
We report the robust self-organisation of the vortex lattice domains to
elongated parallel stripes perpendicular to the applied current in a
steady-state. The experimental results for the formation of the superstructure
are supported by theoretical calculations, which highlight important details of
the vortex matter evolution. The investigation demonstrates a mechanism of a
spontaneous pattern formation that is closely related to the universal physics
governing the intermediate mixed state in low-$\kappa$ superconductors.
