Main chamber high recycling on ASDEX upgrade

Main chamber recycling has been quantified over a wide range (Ip = 0.6–1.1 MA, Bt = −3 to −1.9 T, ne = 0.3–1 × 1020 m−3, Ptot = 2.5–20 MW), both inter-ELM and during type-I ELMs. A vertical CO2 interferometer channel registers densities δneLV2 in excess of those expected from core/SOL parameters. δneLV2 is localized at the inner, lower divertor baffle in the main chamber. Its behavior follows the neutral fluxes measured by a nearby pressure gauge. Particle fluxes to the inner wall as well as densities exhibit parallel behavior. δneLV2 can be as high as 8 × 1019 m−2 and the ELM perturbation itself as large as 9 × 1019 m−2. ne at the inner wall reaches 2.5 × 1020 m−3 and fluxes ∼6 × 1023 s−1. For controlled conditions δneLV2 is linear with ne and increases with Ptot. A ne threshold increasing with Ip exists below which δneLV2 ∼ 0, corresponding to a Greenwald density <0.45. These results suggest enhanced SOL transport, both inter-ELM and during ELMs, on the high field side leading to these appreciable plasma-wall interactions.