Intermittent transport across the scrape-off layer: latest results from ASDEX Upgrade

Abstract

Abstract.We report the latest results of turbulence and transport studies in the ASDEX Upgrade scrapeoff layer (SOL). Dissimilarity between the plasma and the floating potential fluctuations is studied experimentally and by gyrofluid simulations. Measurements by a retarding field analyzer reveal that both, ELM and turbulent filaments convey hot ions over large radial distances in the SOL. The measured far SOL ELM ion temperature increases with the ELM energy, consistent with earlier observations that large ELMs deposit a large fraction of their energy outside the divertor. In the SOL, the ELM suppression by magnetic perturbations (MPs) results into lower ELM ion energy in the far SOL. At the same time, large filaments of ion saturation current are replaced by more continuous bursts. Splitting of the divertor strike zones observed by the infrared imaging in H-mode with MPs agree with predictions from the EMC3-Eirene simulations. This suggests that the 'lobe' structures due to perturbation fields observed near the X-point are not significantly affected by plasma screening, and can be described by a vacuum approach, as in the EMC3-Eirene. Finally, some effects of the MPs on the L-mode SOL are addressed.

Turbulent fluctuations during pellet injection into a dipole confined plasma torus

“…Interpretation of particle flux from the probe array measurements are not easy because the edge fluctuations are very large and because the electron temperature fluctuations cannot be independently measured. 25,26 Nevertheless, the turbulent particle flux estimated using the probe array is important and relevant because these estimates are consistent with independent means to measure particle transport, and changes in estimated flux during pellet injection are consistent with theoretical expectations. Both before and after the pellet injection, the particle flux is inward as measured with the interferometer array.…”

“…IV, the fluctuations in the edge are sufficiently large to cause negative current spikes in the ion saturation current, which we hypothesize results from the rapid outward transport of superthermal electrons. As discussed by Gennrich and Kendl 25 and Kočan and co-authors, 26 the assumption of the equivalency of the floating and plasma potential fluctuations tends to over estimate particle flux. On the other hand, because the phase shift between the density and temperature fluctuations can be small, the direction of the radial particle flux may still be correctly estimated.…”

The effects of magnetic topology on the scrape-off layer turbulence transport in the first divertor plasma operation of Wendelstein 7-X using a new combined probe

“…The conditional averaging method is used to illustrate the properties of fast events on the ion saturation current and radial turbulent particle flux. The conditional averaging of 𝐼 𝑠 has a FWHM of about 13 μs, which is similar to the time scale of blobs in some fusion devices [62,63]. Besides these fast events, an obvious oscillation around 10-20 kHz is accompanied with the fast events, and the turbulence within this frequency range dominates the radial transport as shown in the frequency distribution of Γ 𝑟 (𝑓, 𝑅).…”

The impact of the fast ion fluxes and thermal plasma loads on the design of the ITER fast ion loss detector

“…This is comparable to surface heat load on the reciprocating Langmuir probes in the current tokamaks (e.g. [11]) and is significantly larger compared to lost alpha particle heat flux of 1 MW/m 2 , estimated from ASCOT simulations [4].…”