Reconstruction of the radiation emitted by the intrinsic impurities in the RFX reversed field pinch

Experimental data concerning line, continuum radiation and total radiated power emitted by the intrinsic impurities (carbon and oxygen) in the RFX reversed field pinch have been reproduced with a one-dimensional time-dependent collisional radiative impurity diffusion model. The reconstruction has been performed both in discharges with fixed current at different densities and with different currents at fixed density. The results of the model confirm the relatively low Zeff values measured in RFX at all current levels, despite the high power flow to the wall. A diffusion coefficient of 20 m2 s-1 at the centre of the plasma, decreasing to 1 m2 s-1 at the edge, and a pinch velocity which is outwardly directed in the central region and inward at the edge have to be used to simulate the experimental data. The diffusion coefficient behaviour deduced for light impurities is coherent with the transport properties deduced for the main plasma species and is consistent with a plasma in which the confinement region is localized at the edge, where strong density gradients have been observed; the pinch velocity profile characteristics agree with the plasma radial flow resulting from three-dimensional nonlinear MHD codes.