Enhanced Confinement and Quasi-Single-Helicity Regimes Induced by Poloidal Current Drive

Enhanced confinement regimes with quasihelical symmetry are reproducibly obtained in the modified reversed field pinch eXperiment (RFX)-mod by reducing the level of internal chaos through the combination of a smooth magnetic boundary (through a virtual shell scheme) and the oscillating poloidal current drive technique. The plasma moves from a chaotic multiple helicity towards a quasi-single-helicity regime with a magnetic island showing high temperature and soft x-ray emissivity. The chaos reduction involves also the plasma outside the island allowing for a global enhanced confinement with an improvement up to 50%.