Gyrokinetic simulations of ion temperature gradient mode and trapped electron
mode driven impurity transport in a realistic tokamak geometry are presented
and compared with results using simplified geometries. The gyrokinetic results,
obtained with the GENE code in both linear and non-linear modes are compared
with data and analysis for a dedicated impurity injection discharge at JET. The
impact of several factors on heat and particle transport is discussed, lending
special focus to tokamak geometry and rotational shear. To this end, results
using s-alpha and concentric circular equilibria are compared with results with
magnetic geometry from a JET experiment. To further approach experimental
conditions, non-linear gyrokinetic simulations are performed with collisions
and a carbon background included.
The impurity peaking factors, computed by finding local density gradients
corresponding to zero particle flux, are discussed. The impurity peaking
factors are seen to be reduced by a factor of ~2 in realistic geometry compared
with the simplified geometries, due to a reduction of the convective pinch. It
is also seen that collisions reduce the peaking factor for low-Z impurities,
while increasing it for high charge numbers, which is attributed to a shift in
the transport spectra towards higher wavenumbers with the addition of
collisions. With the addition of roto-diffusion, an overall reduction of the
peaking factors is observed, but this decrease is not sufficient to explain the
flat carbon profiles seen at JET.Comment: 19 pages, 9 figures (17 subfigures
