Electromagnetic filaments and edge modifications induced by electrode biasing in the RFX-mod tokamak

The occurrence of improved confinement regime, H - mode, in magnetic plasma confinement devices is characterized by the creation of an edge transport barrier and a reduction in the turbulence level s. Such reduction is usually associated with a massive shear in plasma flow at the edge, impacting on dynamic and features of blobs or filament. These structures emerging from turbulence background in the SOL are responsible for a huge loss of particles an d energy . Edge Localized Modes (ELMs) large filaments often appear at the plasma edge during the H - mode and are related to a quasi - periodic relaxation of the transport barrier. Although much information about ELMs has been gathered in the last few years, e nabling even the successful mitigation of them, their underlying physical characteristics ( i.g. their electromagnetic behaviour in different scales) are, in a certain sense, still obscure. Filament behaviour has been reported in the ELMs, bringing an inter esting parallel with the turbulent structures in the L - mode . In this contribution w e have been studying transition s to H - mode induced by electrode biasing at the edge of the RFX - mod experiment operating in tokamak configuration. The electromagnetic fluctua tion s and the equilibrium of the plasma parameters at edge were measured by insertable probe head, U - probe, before and during the biasing phase. They have been addressed to determine in which conditions the H mode is reached in the RFX (i.g. if there are i ntermediate phases ) . The different st ructures occurring during the H - Mode phase have been studied, including ELM and the inter ELM phase . Advanced statistical methods have been applied to simultaneous analysis of different plasma parameters such as the electron temperature , the electron density and the vorticity, as well as magnetic signals measured by a set of pick - up coils installed in the probe head . A detailed comparison of the electromagnetic features of the filaments occurre nce before and during the H - mode has been done, with a special attention to the electromagnetic ELM fine structure , through the analysis in different scales.