Numerical studies of particle transport in RFX-mod low chaos regimes

In the Reversed Field Pinch (RFP) configuration the plasma can access regimes in which a single tearing mode dominates the magnetic perturbations spectrum (Quasi Single Helicity state, QSH) [1]. Thermal measurements performed in the RFX-mod experiment [2] (Padua, Italy) during QSH states have shown clear helical structures, identified by significant temperature gradient in the plasma core, which can reach a considerable size (25-50% of plasma radius) and temporal persistance up to 85% the flat top phase (~200ms) of the discharge [3]. In this work we study some aspects of the transport mechanisms relevant to these conditions: on the one hand the impact of residual magnetic chaos, on the other hand the effect of electrostatic micro-instabilities, the latter have been overlooked in the past when the RFP configurations where frequently dominated by turbulent chaotic regimes (so-called MH regimes). We shall here consider the best perfomance discharges (plasma current Ip ~1.0-1.3MA and electron density ne ~2-4?1019 m-3) characterized by QSH regimes with separatrix expulsion from the helical core [4].