Radio-Frequency Power Injection and Impurity Profile Control in JET
The idea of adopting Tungsten as the material for several Plasma Facing Components in ITER emphasizes the importance of understanding the transport that governs heavy impurities in low collisionality H-mode discharges and the ways to control their core concentrations. Various experiments worldwide have shown that electron heating by means of Radio Frequency power does flatten the impurity density. In the RF induced outward flow of Si traces was justified as due to Trapped Electron Modes (TEM) on the basis of gyro-kinetic calculations. In the nonlinear gyro-kinetic simulation applied to ITER scenarios predict that the convection of impurities is usually directed inwards for ion heat fluxes which exceed or are equal to the electron heat flux, but can reverse direction in conditions in which the electron heat flux exceeds significantly the ion heat flux. In JET, various type of discharges at ITER relevant collisionality (veff ~ 0.1) had shown that both Ni (A = 28) and Mo (A = 42) feature flat or slightly hollow density profiles when ICRH is applied.