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The global build-up to intrinsic edge localized mode bursts seen in divertor full flux loops in JET
Univ Warwick, Dept Phys, Ctr Fus Space & Astrophys, Coventry CV4 7AL, W Midlands, England.;Max Planck Inst Phys Komplexer Syst, Dresden, Germany.;Univ Warwick, Dept Phys, Coventry CV4 7AL, W Midlands, England..
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Fusion Plasma Physics.
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Number of Authors: 11112015 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 7, article id 072506Article in journal (Refereed) Published
Abstract [en]

A global signature of the build-up to an intrinsic edge localized mode (ELM) is found in the temporal analytic phase of signals measured in full flux azimuthal loops in the divertor region of JET. Toroidally integrating, full flux loop signals provide a global measurement proportional to the voltage induced by changes in poloidal magnetic flux; they are electromagnetically induced by the dynamics of spatially integrated current density. We perform direct time-domain analysis of the high time-resolution full flux loop signals VLD2 and VLD3. We analyze plasmas where a steady H-mode is sustained over several seconds during which all the observed ELMs are intrinsic; there is no deliberate intent to pace the ELMing process by external means. ELM occurrence times are determined from the Be II emission at the divertor. We previously [ Chapman et al., Phys. Plasmas 21, 062302 (2014); Chapman et al., in 41st EPS Conference on Plasma Physics, Europhysics Conference Abstracts (European Physical Society, 2014), Vol. 38F, ISBN 2-914771-90-8] found that the occurrence times of intrinsic ELMs correlate with specific temporal analytic phases of the VLD2 and VLD3 signals. Here, we investigate how the VLD2 and VLD3 temporal analytic phases vary with time in advance of the ELM occurrence time. We identify a build-up to the ELM in which the VLD2 and VLD3 signals progressively align to the temporal analytic phase at which ELMs preferentially occur, on a similar to 2 - 5ms timescale. At the same time, the VLD2 and VLD3 signals become temporally phase synchronized with each other, consistent with the emergence of coherent global dynamics in the integrated current density. In a plasma that remains close to a global magnetic equilibrium, this can reflect bulk displacement or motion of the plasma. This build-up signature to an intrinsic ELM can be extracted from a time interval of data that does not extend beyond the ELM occurrence time, so that these full flux loop signals could assist in ELM prediction or mitigation.

Place, publisher, year, edition, pages
AMER INST PHYSICS , 2015. Vol. 22, no 7, article id 072506
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Fusion, Plasma and Space Physics
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URN: urn:nbn:se:kth:diva-269396DOI: 10.1063/1.4926592ISI: 000358933600032Scopus ID: 2-s2.0-84937057185OAI: oai:DiVA.org:kth-269396DiVA, id: diva2:1413128
Note

QC 20200309

Available from: 2020-03-09 Created: 2020-03-09 Last updated: 2020-03-09Bibliographically approved

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Bergsåker, HenricBykov, IgorElevant, ThomasFrassinetti, LorenzoGarcia-Carrasco, AlvaroHellsten, TorbjörnIvanova, DaryaJohnson, ThomasMenmuir, SheenaPetersson, PerRachlew, ElisabethRubel, MarekStröm, PetterTholerus, EmmiWeckmann, Armin
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