The physics of large and small edge localized modes

The operational boundaries for the occurrence of various types of edge localized mode (ELM) instability in high-confinement-mode (H-mode) fusion plasmas are reviewed. The phenomenology of ELMs and the occurrence of different ELM types in parameter space are described. Favourable ELM regimes are observed in various experiments which combine small ELM losses with high edge pressure and thereby allow for good H-mode confinement even in situations where core confinement is strongly dependent on edge parameters. Recent progress of ELM models based on ideal or resistive MHD is described and their ability to describe the various ELM regimes discussed. (author)