Abstract We discuss a possibility of extracting impurities at the plasma edge, which is based on the application of a RF electric field, combined with the presence of a modulation of the static magnetic field around the major axis. The principle of the method is to increase the transverse energy of the impurity ions at the plasma edge by cyclotron resonance. Under the influence of the RF field, these ions eventually become trapped in the local mirrors due to the modulation of the magnetic field and then drift outside the plasma. We first compute the probability of extraction of an impurity ion when it meets the resonance region; this lays down a condition on the minimum RF field which should be applied. This RF field may be created as Alfven waves either compressional (propagating radially) or torsional propagating along the flux lines.