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Nuclear Fusion Volume 49 Number 12 Create an alert RSS this journal

M.N.A. Beurskens et al 2009 Nucl. Fusion 49 125006 doi:10.1088/0029-5515/49/12/125006

Pedestal and scrape-off layer dynamics in ELMy H-mode plasmas in JET

M.N.A. Beurskens1,9, A. Alfier2, B. Alper1, I. Balboa1, J. Flanagan1, W. Fundamenski1, E. Giovannozzi3, M. Kempenaars1, A. Loarte6, P. Lomas1, E. de La Luna4, I. Nunes7, R. Pasqualotto2, R.A. Pitts6, G. Saibene8, M. Walsh1, S. Wiesen5 and JET-EFDA contributors

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Abstract References Cited By

Pedestal and scrape-off layer (SOL) dynamics due to edge localized modes (ELMs) have been studied on JET with improved diagnostic capability. The new high resolution Thomson scattering system enables detailed measurement of the space and time evolution of the Te and ne pedestal profiles. The pedestal and SOL dynamics for type I ELMy H-mode plasmas have been studied for a wide range of plasma conditions. During a short period of <200 µs after the ELM event radial profiles of filaments in the SOL electron density and temperature have been observed. After that period the SOL density is increased and remains high for several milliseconds. During the same period the electron temperature shows no increase compared with the pre-ELM values. This SOL dynamics has been observed for a wide range of plasma parameters and is independent of plasma pedestal collisionality. For the first time on JET the convective and conductive ELM energy losses have been quantified using the new kinetic profile measurements. The findings provide detailed confirmation of earlier observations based on different measurements and analysis. The pedestal region perturbed by the ELM is the same for both density and temperature and the ELM effect extends up to about 20% of minor radius. The convective energy losses do not vary significantly and are ~5% of the pedestal stored energy (Wped) over a large range of pedestal collisionality \nu_{\rm e}^\ast from below \nu_{\rm e}^\ast =0.1 to above \nu_{\rm e}^\ast =0.5 whereas the conductive losses strongly decrease from ~20% of Wped to 5% of Wped with increasing \nu_{\rm e}^\ast . The experimental observations are compared with a simple model based on losses being driven by parallel transport.


PACS

52.55.Fa Tokamaks, spherical tokamaks

28.52.Fa Materials

52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

28.52.Lf Components and instrumentation

52.70.-m Plasma diagnostic techniques and instrumentation

52.40.Hf Plasma-material interactions; boundary layer effects

Subjects

Instrumentation and measurement

Nuclear physics

Plasma physics

Dates

Issue 12 (December 2009)

Received 22 May 2009, accepted for publication 17 September 2009

Published 10 November 2009



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