ELM studies on ASDEX

The performance of tokamaks operating in the H-mode crucially depends on the ELM (Edge Localized Mode) behaviour of the discharge. On DIII-D and ASDEX it was found that only in ELMy discharges with a carefully optimized ELM repetition rate stationary conditions could be achieved. Nevertheless, the nature of the ELM as an MHD phenomenon is not yet clear. On DIII-D giant ELMs occur at the ideal ballooning limit while grassy ELMs are found in the connection region of the s - α diagram pointing towards resistive ballooning modes. On the other hand, on PBX-M it was found that ELMs appear in discharges which were analyzed to be ballooning stable and an MHD stability analysis indicated that ELMs could be connected to low-n pressure driven ideal kink modes. (author) 8 refs., 2 figs