The H-mode in COMPASS-D

Abstract

H-mode confinement is observed in COMPASS-D in ohmic and ECR heated single null divertor configuration discharges over a wide parameter range. At low densities the L - H transition power threshold shows a sharp increase, in contrast to scaling law behaviour. Transition to ELM-free H-mode is better correlated with a critical value of plasma pressure than edge power density. In experiments influencing H-mode dynamics, edge current density is found to be destabilizing, suggesting the possible role of the peeling mode. ELM characteristics are discussed, and impurity rotation observations and derived radial electric fields presented.