  Laser blow-off injections of aluminum and tungsten have been performed on the
DIII-D tokamak to investigate the variation of impurity transport in a set of
dedicated ion and electron heating scans with a fixed value of the external
torque. The particle transport is quantified via the Bayesian inference method,
which, constrained by a combination of a charge exchange recombination
spectroscopy, soft X-ray measurements, and VUV spectroscopy provides a detailed
uncertainty quantification of the transport coefficients. Contrasting discharge
phases with a dominant electron and ion heating reveal a factor of 30 increase
in midradius impurity diffusion and a 3-fold drop in the impurity confinement
time when additional electron heating is applied. Further, the calculated
stationary aluminum density profiles reverse from peaked in electron heated to
hollow in the ion heated case, following a similar trend as electron and carbon
density profiles. Comparable values of a core diffusion have been observed for
W and Al ions, while differences in the propagation dynamics of these
impurities are attributed to pedestal and edge transport. Modeling of the core
transport with non-linear gyrokinetics code CGYRO [J. Candy and E. Belly J.
Comput. Phys. 324,73 (2016)], significantly underpredicts the magnitude of the
variation in Al transport. The experiment demonstrates a 3-times steeper
increase of impurity diffusion with additional electron heat flux and 10-times
lower diffusion in ion heated case than predicted by the modeling. However, the
CGYRO model correctly predicts that the Al diffusion dramatically increases
below the linear threshold for the transition from the ion temperature gradient
(ITG) to trapped electron mode (TEM).
