Main chamber high recycling on ASDEX upgrade

Main chamber recycling has been quantified over a wide range (I-p = 0.6-1.1 MA, B-t = -3 to -1.9 T, n(e) = 0.3-1 X 10(20) m(-3), P-tot = 2.5-20 MW), both inter-ELM and during type-1 ELMs. A vertical CO2 interferometer channel registers densities delta n(e)LV2 in excess of those expected from core/SOL parameters. delta n(e)LV2 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. delta n(e)LV2 can be as high as 8 x 10(19) m(-2) and the ELM perturbation itself as large as 9 x 10(19) m(-2). n(e) at the inner wall reaches 2.5 x 10(20) m(-3) and fluxes similar to 6 x 10(23) s(-1). For controlled conditions delta n(e)LV2 is linear with n(e) and increases with P-tot. A n(e) threshold increasing with I-p exists below which delta n(e)LV2 similar to 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. (C) 2009 Published by Elsevier B.V.