Thermal structures and their relation to magnetic topology in RFX-mod

A statistical analysis of plasma temperature profiles in RFX-mod plasmas reveals that improved thermal structures can be observed in chaotic magnetic topologies, specifically in the so-called multiple helicity (MH) states. The improved thermal structures feature high electron temperatures, up to 1.2 keV, enhanced temperature gradient and radial extension which have been conventionally only attainable in organized quasi-single helicity states. The analysis reported here suggests a possible role of the m = 1, n=-7 and the m = 1, n=-8 modes (where m and n are the poloidal and toroidal mode numbers, respectively) in MH states, where the plasma retains good temperature properties. These findings, also supported by numerical ORBIT simulations, indicate that the magnetic islands of the innermost resonant modes may act as regions of improved energy confinement, opening new avenues for understanding the connection between the plasma's magnetic topology and thermal properties. This paves the way for new sets of experiments in RFX-mod2, with the aim of exploring these mechanics in detail and improving the thermal properties of RFP plasmas.