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Toroidally symmetric, narrow band low frequency (<2 kHz) magnetohydrodynamic (MHD) activity at the plasma edge has been identified during initial phases of dithering L-H transitions in JET. It manifests itself as regular bursts on the divertor D(alpha) emission, and is also observed on magnetic and target Langmuir probes and on edge channels of the reflectometer. The oscillations appear simultaneously with the transition from L-mode phase to the dithering H-mode phase and disappear with the transition to the type III edge localized mode (ELM)y H-mode phase of the discharge. In spite of being regular and in many respects similar to dithering cycles previously observed in ASDEX Upgrade and attributed to repetitive series of L-H-L transitions, these oscillations show clear signatures of ELMs and can be gradually converted into irregular type III ELMs with the increase in edge electron temperature.

Additional information

Authors: CHANKIN A V, RSC Kurchatov Institute, Moscow (RU);ARSHAD S A ET AL, JET Joint Undertaking, Abingdon, Oxon (GB)
Bibliographic Reference: Report: JET-P(97)23 EN (1997) 7pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon, OX14 3EA (GB)
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