Relation Between Type-II ELMs, Edge Localized Turbulence, Washboard Modes and Energy Losses Between ELMs in High Density ELMy H-modes on JET

A characteristic feature of ELMy H-mode regimes with so-called mixed type-I/II edge localized modes is a change in the magnetic fluctuation spectrum measured with pick-up coils near the plasma boundary. The power losses in-between ELMs can be attributed to so-called washboard modes, i.e. bands of small-scale MHD modes rotating in the electron diamagnetic drift direction, which become more pronounced in these plasmas. The washboard modes can cause a saturation of the edge temperature, but they are not strong enough to stop the evolution of the edge density. The onset of the ELM precursor modes suppresses the washboard bands and allows the pedestal pressure to build-up faster, which leads eventually to the ELM crash.
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