Modelling of Impurity Transport Experiments at the Joint European Torus
Impurity transport in JET is studied using interpretative analysis and predictive simulations of JET discharges. The simulations are based on transport models for Ion-Temperature-Gradient (ITG) mode and Trapped-Electron (TE) mode driven turbulence and neoclassical transport. The properties of the impurity transport coefficients obtained with fluid as well as quasi-linear and nonlinear gyrokinetic simulations using the code GENE are compared and discussed. In particular, the sign of the impurity convective velocity (pinch) and the scaling of the normalised impurity density peaking factor -RnZ/nZ with impurity charge number is investigated. Predictive simulations of temperatures (Te, Ti = TZ) and densities (ne, nZ) are performed with the JETTO/SANCO core transport code. The scaling of impurity transport with impurity charge Z is crucial for the performance and optimisation of a fusion reactor. In the present study, a set of dedicated JET impurity injection experiments are analysed. The impurities were injected by laser ablation (Ni) and gas injection (Ne, Ar) and the diffusivity DZ and convective velocity VZ were determined by matching spectroscopic data with predictive results obtained with the transport code UTC-SANCO.