This paper reports results on measurements of the density profiles. Here we analyse the behaviour of the electron
density for a set of experiments in type I ELMy H-mode discharges in ASDEX Upgrade where the plasma current,
plasma density, triangularity and input power were varied. Detailed measurements of the radial extent of the
perturbation on the density profiles caused by the edge localized mode (ELM) crash (ELM affected depth), the
velocity of the radial propagation of the perturbation as well as the width and gradient of the density pedestal are
determined. The effect of a type I ELM event on the density profiles affects the outermost 20–40% of the plasma
minor radius. At the scrape-off layer (SOL) the density profile broadens while in the pedestal region the density
decreases resulting in a smaller density gradient. This change in the density profile defines a pivot point around which
the density profile changes. The average radial velocity at the SOL is in the range 125–150 ms−1 and approximately
constant for all the density layers far from the pivot point. The width of the density pedestal is approximately constant
for all the ELMy H-mode discharges analysed, with values between 2 and 3.5 cm. These results are then compared
with an analytical model where the width of the density is predominantly set by ionization (neutral penetration
model). The width of the density profiles for L-mode discharges is included, since L- and H-mode have different
particle transport. No agreement between the experimental results and the model is found. |