Journal Article

FZJ-2021-05646

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png The role of edge plasma parameters in H-mode density limit on the JET-ILW

Sun, H. J.FZJ* ; Goldston, R. J. ; Huber, A. (Corresponding author)FZJ* ; Xu, X. Q.FZJ* ; Flanagan, J. ; McDonald, D. C. ; de la Luna, E. ; Maslov, M. ; Harrison, J. R. ; Militello, F. ; Fessey, J. ; Cramp, S.

2021
IAEA Vienna

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Please use a persistent id in citations: http://hdl.handle.net/2128/29933  doi:10.1088/1741-4326/abf056

Abstract: A study of a dataset of JET H-mode plasma with the Be/W ITER-like wall (JET-ILW) shows that reaching the edge MHD ballooning limit leads to confinement degradation. However, unlike JET plasmas with a carbon wall (JET-C), the JET-ILW plasmas stay in a marginal dithering phase for a relatively long period, associated with a higher (≈20%) H-mode density limit (HDL) than JET-C equivalents. This suggests that ITER could be operated in H-mode with higher density than the scaling based on carbon wall devices, but likely with a dithering phase plasma with lower confinement. A new, reliable estimator for JET Er, min has been derived by combining HRTS measurements of pedestal gradient and edge-SOL decay lengths. JET radial Er ETB wells are observed in the range of −15 to −60 kV m−1 in high performance H-modes, consistent with previous CXRS results in ASDEX Upgrade. The results imply that a higher positive E × B shear in the near SOL plays a role in sustaining a marginal phase in JET-ILW which leads to a higher HDL than that in JET-C. The results of the JET-ILW dataset show agreement with the Goldston finite collisionality HD model for SOL broadening at high collisionality. A hypothesis for the dithering H-mode phase is proposed: as ne,SOL increases, ν∗,SOL increases, SOL broadens, Er shear decreases, triggers L-mode; ne drops, ν∗,SOL decreases, SOL becomes narrower, and Er shear increases, triggering H-mode, resulting in a cycle of H–L–H- oscillations. For burning plasma devices, such as ITER, operating just below the MHD limit for the dithering phase could be a promising regime for maximising core density, and fusion performance while minimising plasma-material interaction. The oscillatory signal during the dithering phase could be used as a precursor of undesirable plasma performance for control purposes.

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Contributing Institute(s):

1. Plasmaphysik (IEK-4)
2. Modellierung von Energiesystemen (IEK-10)

Research Program(s):

1. 134 - Plasma-Wand-Wechselwirkung (POF4-134) (POF4-134)

Appears in the scientific report 2021

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Database coverage:
; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; Essential Science Indicators ; IF < 5 ; JCR ; National-Konsortium ; Nationallizenz ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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