Operational limits for high edge density H-mode tokamak operation

摘要

Operational regime boundaries for High confinement mode (H-mode) plasmas with high edge density are invest gated on the ASDEX Upgrade tokamak. In addition to the MHD stability boundary imposed by Edge Localize Modes (ELMs) and the H-mode threshold, the onset of complete divertor detachment limits the accessible separate density. At the H-mode density limit, a transport enhancement is observed that reduces the temperature gradient in to edge of the main plasma and can lead to a disruption by loss of H-mode and and subsequent radiation and resistive MHD instability. This 'transport limit' occurs parallel to full divertor detachment at high edge collisionalities, possible origin is drift-Alfven-ballooing turbulence driven by the pressure gradient at high collisionality.