Effect of plasma shape variation on ELMs and H-mode pedestal properties in ASDEX Upgrade

Abstract

The effect of plasma shape variation (in particular, variation of the upper and lower triangularity δ) on edge localized modes (ELMs) and H-mode pedestal properties in ASDEX Upgrade is reported here. Strongly shaped plasmas (high δ) show an increased edge pressure gradient and, without external gas puff, type-I ELMs generally have larger losses and lower frequency than in plasmas with low δ. With external gas puff, ELM losses at high δ are reduced and in the same range as found for low δ. The average ELM power loss is a constant fraction of the total loss power, independent of triangularity. The width of the steep electron temperature and pressure gradient zone remains essentially constant at low δ while at high δ it shows a variation inconsistent with a poloidal gyroradius scaling. The edge pressure gradient and the pedestal pressure scales strongly with plasma current and triangularity. In type-I ELM H-modes, the pedestal pressure is directly related to the global stored plasma energy, independent of plasma shape.