Abstract. Recently, comprehensive studies on Dynamic Ergodic Divertor (DED) have re-started by us stimulated by the coming realization of the concept on TEXTOR tokamak. The following aspects of interaction of rotating helical magnetic perturbation (RHMP) with plasmas in HYBTOK-II and CSTN-IV small tokamaks will be given: the penetration of RHMP into the magnetic resonance layer with a controlled poloidal rotation by limiter biasing, the effects on hydrogen recycling, the influence on the electrostatic turbulence through chaos control with a wavelet signal analysis, and the global effects of RHMP on tokamak discharge like an additional poloidal rotation and a local dissipative heating. Especially, an amplified magnetic perturbation was found to be created near the resonance layer by a spatial modification of plasma current due to island formation in the case of low relative velocity between the tokamak plasma and RHMP. A large relative velocity produces an expected attenuation of RHMP near the resonance zone due to flowing of screening current.