Anomalous impurity transport in tokamaks in the presence of RF fields

Paper in proceeding, 2008

Recent experiments1-4 have shown that auxiliary heating can influence impurity accumulation in Tokamaks. In the present study the transport of impurities by Ion-Temperature-Gradient (ITG) and Trapped-Electron (TE) mode turbulence in the presence of radio frequency (rf) fields in the ion cyclotron range of frequencies is investigated using an electrostatic, collisionless fluid model. The turbulence is affected by the ponderomotive force associated with the rf field of the fast magnetosonic wave in the plasma. It is shown that the inward impurity convective velocity (pinch) and diffusivity can be reduced by the rf field, in particular close to the wave resonance location where the ponderomotive force may be significant. However, the steady state impurity density peaking factor -∇nz/nz does not seem to be as strongly affected by the rf field as indicated by recent tokamak experiments.