Confinement regimes in simple magnetized toroidal plasmas

In the simple magnetized torus TORPEX (R = 1 m, a = 0.2 m), we explore experimentally the accessibility of a high confinement mode, which is predicted by theory for this configuration [P. Ricci, et al., Phys. Rev. Lett. 100, 225002 (2008)]. We consider different gases (H2, D, He, Ne, N2) and we measure the dependence of the temperature and density gradients upon the ratio γ/v’ExB (γ is the interchange linear growth rate and v’ExB is the velocity shear). We observe that gamma/v’ExB decreases from γ/v’ExB6-7 for hydrogen to γ/v’ExB0.3-0.4 for neon. Consistently with theory, temperature and density profiles steepen when γv’ExB drops below unity. The perpendicular particle flux is estimated by particle balance and measured using a multi-pin flux probe. First simulation results are presented with a global fluid code that solves the drift-reduced Braginskii equations in the whole TORPEX domain.