Edge stability analysis of high βp plasmas

An MHD stability analysis of the edge plasma shows that in highly triangular plasmas, the increasing global βp has a stabilizing effect on the low-n instabilities that trigger edge localized modes (ELMs). The improved stability allows the access of higher edge pressure gradients before the ELM is triggered. At the same time, the edge plasma moves closer to the high-n ballooning mode stability boundary. The stability changes can explain why the high value of βp helps to access smaller ELMs. (Some figures in this article are in colour only in the electronic version)