3D active modulation of edge topology in toroidal devices: effects on turbulent electromagnetic filaments

Filament or blob structures have been observed in all magnetic configurations with very similar features despite the difference in the magnetic geometry, and are believed to play an important role in convecting particle and energy towards the wall. Despite their possibly different generation mechanism, turbulent structures and Edge Localized Mode (ELM) filaments share some common physical features. The electromagnetic (EM) effects on filament structures deserve particular interest [1], among the others for the implication they could have for ELM, related for instance to their dynamics in the transition region between closed and open field lines or to the possibility, at high beta regimes, of causing line bending which could enhance the interaction of blobs with the first wall. A direct characterization of the effects of active modification of the edge topology on electromagnetic (EM) turbulent filament structures is presented, comparing Reversed Field Pinch (RFP) and tokamak configurations. Measurements are obtained in the RFX-mod device, which allows operating in both configurations and with different equilibria and is also equipped with an advanced system for the edge magnetic feedback control. Different case studies of actively controlled magnetic perturbations (MP) will be analyzed focusing on the filament interaction with local magnetic islands [2,3]. High frequency fluctuations, characterizing electrostatic and magnetic filament features, and the associated transport coefficients have been observed to be strongly affected by the island proximity and topology. These observations highlight a tight correlation between the small scale EM filamentary structures and the applied MP, opening the challenging possibility of active control of filaments and their related transport by modulation of the local magnetic topology.