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research article

Plasma-edge gradients in L-mode and ELM-free H-mode JET plasmas

Breger, P.
•
Flewin, C.
•
Zastrow, K. D.
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1998
Plasma Physics and Controlled Fusion

Experimental plasma-edge gradients in JET during the edge-localized-mode (ELM) free H-mode are examined for evidence of the presence and location of the transport barrier region inside the magnetic separatrix. High spatial resolution data in electron density is available in-and outside the separatrix from an Li-beam diagnostic, and in electron temperature inside the separatrix from an ECE diagnostic, while outside the separatrix, a reciprocating probe provides electron density and temperature data in the scrape-off layer. Ion temperatures and densities are measured using an edge charge-exchange diagnostic. A comparison of observed widths and gradients of this edge region with each other and with theoretical expectations is made. Measurements show that ions and electrons form different barrier regions. Furthermore, the electron temperature barrier width (3-4 cm) is about twice that of electron density, in conflict with existing scaling laws. Suitable parametrization of the edge data enables an electron pressure gradient to be deduced for the first time at JET. It rises during the ELM-free phase to reach only about half the marginal pressure gradient expected from ballooning stability before the first ELM. Subsequent type I ELMs occur on a pressure gradient contour roughly consistent with both a constant barrier width model and a ballooning mode envelope model.

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Type
research article
DOI
10.1088/0741-3335/40/3/001
Web of Science ID

WOS:000072905800001

Author(s)
Breger, P.
Flewin, C.
Zastrow, K. D.
Davies, S. J.
Hawkes, N. C.
Konig, R. W. T.
Pietrzyk, Z. A.
Porte, L.  
Summers, D. D. R.
von Hellermann, M. G.
Date Issued

1998

Published in
Plasma Physics and Controlled Fusion
Volume

40

Issue

3

Start page

347

End page

359

Subjects

JET

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
CRPP  
SPC  
Available on Infoscience
April 16, 2008
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/21542
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