Impurity transport studies in the Madison Symmetric Torus reversed-field pinch during standard and pulsed poloidal current drive regimes

The transport of intrinsic impurities is investigated during standard and improved confinement regimes of the Madison Symmetric Torus (MST) reversed-field pinch. The impurity diffusion coefficient (D) and pinch velocity (v) are obtained through comparing the time evolution of experimental impurity density profiles with the results of a one-dimensional impurity transport code. Experimental hollow fully stripped (C, O, B) ion populations in improved confinement discharges are reproduced with the transport code indicating outward convection of impurity ions. Estimated D and v are low and close to classical values. Standard MST discharges are characterized by a high level of stochasticity and nearly flat radial profiles of the fully stripped carbon. To reproduce this flat impurity profile a high outward convective velocity and high central D are assumed in the simulation.