The characteristics of the impurity transport in the RFX reversed field pinch experiment during enhanced confinement regimes, such as those obtained performing pulsed poloidal current drive and oscillating poloidal current drive, have been investigated. It is found that during the enhanced confinement period, the ratio between the Ly α line of C VI and the resonance line of C V increases systematically well beyond the expected enhancement due to the temperature improvement.Experimental data have been reproduced by means of a one-dimensional, time dependent, collisional–radiative impurity transport code, which simulates several C and O lines, continuum emission and radiated power. In standard RFX plasmas the typical diffusion coefficient is ∼20 m2 s−1 at the plasma centre decreasing to ∼1 m2 s−1 at the edge. Best simulations of the spectroscopic data during the enhancement confinement phases are obtained by expanding the low diffusion region at the edge from r/a = 0.9 to r/a = 0.8±0.05 and shrinking the neutral density profile at the edge.
Confinement improvement with RF poloidal current drive in the reversed field pinch