Modeling of AUG pellet discharges

Particle transport in tokamaks has been widely investigated both experimentally and
theoretically over the last 2 decades, advancing our physics understanding, in particular
for the density peaking. The density perturbation by pellet injection allows to decouple
particle diffusion and convection, while only their ratio matters to determine the peaking
at steady-state. In this paper we analyze a pellet frequency scan in ASDEX Upgrade, at fixed pellet mass . and velocity. At lower frequency the density profile has time to relax to the state before . the injection, at higher frequency there is a secular increase of the plasma density as the . profile remains hollow. This suggests a critical transport time scale, thus providing a
constraining test for transport models. The profile evolution is first simulated with ad-hoc models of region-wise uniform particle . diffusivity, constant in time. In this way we characterize the transport level inside and . outside the pellet deposition region. The effect of a particle pinch is also investigated. Then the TGLF model is used for the predictive study, with both saturation rules. The modeling results are presented and the eventual shortcomings are discussed.