Description
Millimeter-sized pellets are, for all practical purposes, the only way to fuel plasmas in a
future fusion reactor. The injection of such a pellet, formed of cryogenic solid hydrogen,
introduces large modifications to the plasma parameters, especially in density and
temperature. The resulting momentary transition of the plasma into a non-stationary state
leads to transport processes that are investigated. This contribution focuses mainly on two
aspects: on the one hand, it discusses the reconstruction of plasma profiles using different
diagnostics at ASDEX Upgrade (Thomson scattering, DCN interferometer, density profiles
from integrated data analysis, pellet ablation radiation monitor) for a special class of pellet
experiments. This special class consists of pellet injections at very low frequency (~5 Hz) into
a presumed stationary plasma, which allows for a statistical treatment of these “single”
repetitive pellets, leading to a significant improvement of the measurements, enabling high-
frequency profile reconstruction for this averaged pellet. On the other hand, these data are
then used for comparison with ASTRA transport simulations, in which the pellet ablation and
the subsequent profile relaxation due to transport processes are calculated, with
applications of the TGLF-SAT2 transport model also demonstrated. Some initial results will
be presented, followed by an outlook on the future of this work.