Characterization of broadband MHD fluctuations during type-II edge localized modes as measured in 2D with ECE-imaging at ASDEX Upgrade

TitleCharacterization of broadband MHD fluctuations during type-II edge localized modes as measured in 2D with ECE-imaging at ASDEX Upgrade
Publication TypeJournal Article
Year of Publication2012
AuthorsJ.E Boom, E. Wolfrum, I.G.J. Classen, P.C de Vries, M. Maraschek, W. Suttrop, C.PP von Thun, A.JH Donne, B.J Tobias, C.W. Domier, NC Luhmann, Jr., H.K Park
JournalNuclear Fusion
Volume52
Number11
Pagination114004
Date PublishedNov
Type of ArticleArticle; Proceedings Paper
ISBN Number0029-5515
KeywordsALCATOR C-MOD, density, GOOD CONFINEMENT, JET, JT-60U, PLASMAS, SMALL ELM REGIMES, STABILITY
Abstract

The characterization of a broadband fluctuation that is typical for the type-II ELM regime at ASDEX Upgrade has been improved using the 2D capabilities of ECE-imaging. During the transition from the type-I to type-II ELMy phase, it has been found that electron temperature fluctuations form a broadband peak in the 19-65 kHz range. In the type-II phase, this broadband fluctuation reaches a maximum relative amplitude of almost 20% just inside the top of the pedestal. Simultaneously, the electron temperature profile is completely flattened at this location. The 2D distribution of the amplitude of this broadband fluctuation is such that, when averaged over time, a minimum occurs around the mid-plane. From the measurements of the nearby magnetic pickup coils, a similar broadband fluctuation seems visible in the same frequency range. However, this is peaked at a slightly lower frequency and does not show a similar minimum. From the analysis of the fluctuations on small timescales, the poloidal and toroidal mode numbers are estimated to be m similar to 100 and n similar to 21. Furthermore, activity reminiscent of beat waves has been observed, which might partially account for the fluctuation's broadband nature and the seeming velocity variation of single fluctuation passages. Overall, similarities between the characteristics of this broadband fluctuation and various precursors to type-I ELMs suggest that this fluctuation can play an important role in regulating the ELM cycle.

DOI10.1088/0029-5515/52/11/114004
Division

FP

Department

PDG

PID

db658b67f92abbfd9d9261fa0480d4d2

Alternate TitleNucl. Fusion
LabelOA

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