Impurity transport in JET L-mode discharges

The transport of intrinsic impurities has been studied in JET (Joint European Torus) L-mode discharges. The analysis reconsiders the question of the convective pinch in the plasma core, which was discussed by Giannella et al. (1994), and an investigation is made of the L-mode edge transport barrier, evidence for which was first presented by Denne-Hinnov et al. (1993). The present study of three, 3.5MA, 3.4T limiter discharges with ∼10MW RF additional heating analyses the radiation, including the VUV and XUV line emission from C and Ni, the only two significant impurities in these discharges. Use has been made of the empirical LINT method to derive elemental radiated power components of the impurities and impurity concentrations. The simulations have been carried out using the 1 1/2-D SANCO impurity transport code with atomic data taken from the ADAS data base. These results show that within experimental uncertainties the inward particle pinch in the bulk of the plasma is negligible and a linear dependence is found between the magnitude of the edge transport barrier and the diffusion coefficient in the outer region of the plasma. Both convective and diffusive barriers have been considered and, using a more precise definition for their magnitude than before, their relative effectiveness quantified. Since it is not possible to determine a unique value for the magnitude of the edge barrier or whether it has a convective or diffusive mechanism for the present intrinsic impurities, which only vary slowly with time, the analysis relating to the edge barrier is applied to the results of Denne-Hinnov et al. who were able to fix the size of the barrier for medium Z elements. (author)