The role of temperature fluctuations in the dynamics of type-I and type-II edge localized modes at ASDEX Upgrade

I.G.J. Classen, J.E. Boom, A. Bogomolov, E. Wolfrum, M. Maraschek, W. Suttrop, P.C. de Vries, A.J.H. Donné, B.J. Tobias, C.W. Domier, N.C. Luhmann

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Two-dimensional temperature measurements using the electron cyclotron emission imaging diagnostic at ASDEX Upgrade revealed a variety of temperature fluctuations associated with type-I and type-II edge localized modes (ELMs). The characteristics and dynamics of these modes, and their role in the ELM cycle, are presented. During type-I ELMs, different phases of distinct mode activity have been identified. At the onset of the ELM crash, a short lived mode is observed in the pedestal region. During the actual crash phase, multiple filamentary structures are observed just outside the separatrix. A third type of fluctuation, the inter-ELM mode, is often observed in between type-I crashes. The occurrence of this mode tends to lengthen the ELM period. During type-I ELM suppression with magnetic perturbation coils, smaller crash events become more frequent, replacing the large type-I crashes. In type-II ELMs, temperature crashes are absent altogether, and a continuous broadband fluctuation in the 20–60 kHz range, showing beat wave like behaviour, is observed. The similarities between the characteristics of this mode and the inter-ELM mode suggest that it is the same instability. In type-I ELMs it delays the next crash, in type-II ELMs it might be responsible for the complete absence of crash events.
Original languageEnglish
Article number073005
Pages (from-to)073005
Number of pages7
JournalNuclear Fusion
Issue number7
Publication statusPublished - 2013


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