EX/P3-9 Improved Confinement with Internal Electron Temperature Barriers in RFX-mod

In RFX-mod the feedback control on multiple magnetohydrodynamic modes allows to improve axysimmetry and to safely operate at high current. RFX-mod reliably operates at 1.5 MA, the highest current ever achieved on a Reversed Field Pinch (RFP). In these high current discharges magnetic topology spontaneously self-organizes in an ohmic helical symmetry, quasi single helicity state ( QSH), in which the magnetic dynamics is dominated by the innermost resonant mode, with the new magnetic axis helically twisting around the geometrical axis of the torus. Inside the helical structure energy confinement is enhanced and electron temperatures exceeding 1 keV are measured, with steep gradients, which identify an internal transport barrier. Separatrix expulsion and symmetric Te profiles with high gradients are obtained for ratios between dominant mode and total B above about 4%. The measured electron temperature peak results nearly symmetric and involves a large fraction of the plasma cross section, corresponding to an improvement of the global electron energy confinement up to a factor 2. Transient strong QSH are reproducibly induced by oscillating poloidal current driven operation (OPCD), also at lower currents (Ip>500kA). The measured steep temperature profiles obtained on QSH conditions correspond to an electron thermal diffusivity diminution by more than one order of magnitude. Perturbative experiments (pellets and impurity laser blow off injections) have been performed to study particle confinement inside and outside the thermal island. Experimental evidences of main gas confinement increasing inside the helical structure have been obtained, while for impurity during a QSH there are no evidences of confinement increase. Plasma energy and particle transport properties are compared with the topological properties of the magnetic field both in standard, or multiple helicity (MH), and QSH cases and compared with numerical simulation result.