Inboard gas puffing and behaviour of H-mode edge parameters in COMPASS-D

Abstract

It is shown that fuelling from the inboard midplane extends the operation window for H-mode in comparison with fuelling from the outboard midplane. In Ohmically heated plasmas, the minimum line-averaged density required for transition to ELM-free H-mode is approximately ~30% lower in comparison with the fuelling from the outboard midplane. The power at the transition to H-mode is similarly reduced. Temporal and spatial resolutions of thermal helium beam, Doppler diagnostics and Thomson scattering were improved to study the edge parameter evolutions during the L-H transitions and ELMs. At L-H and H-L transitions, the diagnostics demonstrate a coincident temporal and spatial evolution of gradients in the radial electric field and electron pressure. During regular ELM behaviour similar evolutions are observed.