Continuous observation of filaments from the confined region to the far scrape-off layer

Abstract

The thermal helium beam diagnostic at ASDEX Upgrade can access the whole plasma edge region simultaneously with a high spatiotemporal resolution. Manifold dynamics of plasma edge transport is observed for different plasma confinement regimes, comprising L- and H-mode scenarios with type-I and small ELMs as well as ELM free EDA regimes. The measurements show that the plasma dynamics in the confined region close to the separatrix is often dominated by regular high frequency modes (10–100 kHz), whereas filaments with an intermittent occurrence rate of 0.1–2 kHz dominate in particular the far scrape-off layer (SOL). The comparison among different regimes shows a similar filamentary activity between L-mode and inter-ELM H-mode phases. An increased filamentary activity in H-mode, however, is found for rising densities n∕nGW. This is the case for the regime of quasi continuous exhaust (QCE) with three times higher filament velocities compared to a clean inter-ELM H-mode.

Keywords

• Plasma filaments
• Scrape-off layer
• Convective transport
• Quasi-coherent modes
• Confinement regimes
• ELM free regimes