Edge turbulence characterization in RFX-mod with optical diagnostics

In the edge region of fusion devices coherent structures (blobs) are commonly observed. In order to investigate their evolution and the possible driving mechanisms, we studied the relationship between the size of the coherent structures and the local characteristic length L(p) of the edge electron pressure profile P(e)(r), together with the effect of magnetic fluctuations on del P(e). The results show an increase in the blob size with both Lp and magnetic fluctuations, suggesting an interplay between electron pressure gradient, magnetic fluctuations and edge turbulence generation. Measurements of the spatial scales of the edge turbulence structures and the corresponding toroidal phase velocity are obtained in the reversed field pinch RFX-mod by means of a gas puffing imaging diagnostic, while the local edge profiles of electron density n(e)(r) and temperature T(e)(r) and therefore P(e)(r) have been measured via the line intensity ratio technique of helium emission lines.