Predictive simulations of impurity transport at JET
Paper in proceedings, 2013
Impurity transport in the Joint European Torus is analysed using the coupling between the transport codes JETTO (for main ions) and SANCO (for impurities) for predictive simulations of dedicated impurity injection experiments. The experimentally injected trace levels of Ne, Ar and Ni in a 2% C background are considered together with numerical experiments covering a broad range of impurities from Be to W. Transport coefficients due to Ion-Temperature-Gradient (ITG) mode and Trapped-Electron (TE) mode turbulence are used together with neoclassical transport from NCLASS. The transport coefficients obtained using the Chalmers fluid model are compared with gyrokinetic results using the code GENE. An updated, multiple ion species version of the Chalmers model called EDWM (Extended Drift Wave Model) has been used for the transport coefficients. Self-consistent simulations of electron and ion temperatures, main ion and impurity densities and toroidal momentum are performed. The role of neoclassical impurity transport is evaluated and the dependence of the simulated profiles on impurity charge number Z, collisionality, ExB shearing, rotation gradient (roto-diffusion), and impurity charge fraction (Zeff) are discussed. For the NBI heated JET L-mode discharges considered, the predictive simulations show that the impurity transport in the bulk of the plasma is dominated by ITG driven transport resulting in impurity peaking factors substantially below the neoclassical predictions for low to intermediate charge numbers. For larger Z-values as well as in the inner core region (ρ<0.2), neoclassical effects are found to be important, resulting in significantly larger peaking factors.