Reversed Field Pinch helical self-organization studies with the volume preserving field line tracing code NEMATO

The existence of a Reversed Field Pinch (RFP) dynamo as a (laminar) helical self-organization was anticipated by MHD numerical studies [1]. High current operation in RFX-mod experiment shows such a helical self-organization: strong internal electron transport barriers (ITB) appear and magnetic chaos healing is diagnosed when Single Helical Axis (SHAx) regimes are achieved [2]. We present results of the field line tracing code NEMATO [3] applied to study the magnetic topology resulting from 3D MHD simulations, with the aim of clarifying the conditions for chaos healing in SHAx states. First tests confirm the basic picture: the magnetic chaos due to island overlap is significantly reduced after the expulsion of the dominant mode separatrix. The possible synergy with the presence of magnetic and/or flow shear at the SHAx ITB will also be discussed [4].\\[4pt] [1] S. Cappello, Plasma Phys. Control. Fusion (2004) {\&} references therein \\[0pt] [2] R. Lorenzini et al., Nature Phys. (2009) \\[0pt] [3] J. M. Finn and L. Chacon, Phys. Plasmas (2005) \\[0pt] [4] M.E. Puiatti et al invited presentation EPS 2009 conference, submitted to Plasma Phys. Control. Fusion