X-point effect on edge stability

Abstract

We study the effects of the X-point configuration on edge localized mode (ELM) triggering peeling and ballooning modes using fixed boundary equilibria and modifying the plasma shape to approach the limit of a true X-point. The current driven pure peeling modes are asymptotically stabilized by the X-point while the stabilizing effect on ballooning modes depends on the poloidal location of the X-point. The coupled peeling–ballooning modes experience the elimination of the peeling component as the X-point is introduced. This can significantly affect the edge stability diagrams used to analyse the ELM triggering mechanisms.