A modification of the flow-reversal effect is considered for a tokamak with externally applied helical magnetic fields and background ion injection, local in φ and multipole in ϑ. Magnetic fields from external helical currents split the rational magnetic surface, giving rise to a chain of magnetic islands. The source of the background ions acts on the impurities through the helical harmonics (m + 1, n) if the islands are produced by the helical magnetic perturbation (m, n).