1 - Nuclear Sciences and Applications - IAEA

THE PLASMA BOUNDARY IN JET
IAEA-CN-50/A-VII-12
L. DE KOCK, P.E. STOTT, S. CLEMENT 1 , S.K. ERENTS 2 ,
P.J. HARBOUR, M. LAUX 3 , G.M. McCRACKEN 2 , C.S. PITCHER 2 ,
M.F. STAMP, P.C. STANGEBY 4 , D.D.R. SUMMERS, A.J. TAGLE
JET Joint Undertaking,
Abingdon, Oxfordshire,
United Kingdom
Abstract
THE PLASMA BOUNDARY IN JET.
The parameters of the scrape-off layer in JET are presented for the case of the new belt limiters
and compared with the earlier case of eight discrete limiters. The scaling with the main plasma
parameters is found to be similar and fits a model that correctly describes the dependence on the mean
plasma density but shows a discrepancy with the input power. — The carbon influx relative to the deuterium
influx, derived from spectroscopic measurements, is compared with the influx calculated from
the measured SOL parameters using the physical sputtering plus carbon self-sputtering and the charged
particle flux on the belt limiter. Both ratios show a decreasing trend with increasing density, although
a discrepancy at low density remains. — The SOL in neutral beam heated discharges, although not
steady state, shows a behaviour comparable with that in OH iimiter discharges. However, in discharges
with radiofrequency heating the SOL parameters are instantaneously affected by the RF power and its
behaviour depends on wall conditions. — Some typical measurements of the SOL parameters in divertor
plasmas are given, showing that in the outer divertor the plasma is hotter than in the inner one (with
correspondingly lower and higher density, respectively). The power flow to the outer divertor is higher
than to the inner one, and the temperature difference indicates that net currents must flow in the SOL.
1. INTRODUCTION
Edge conditions are important in tokamaks as they determine
impurity production by sputtering at the limiter, the ability of
the scrape-off layer to screen impurities frcm the core of the
discharge and the establishment of the H mode of enhanced
confinement in discharges with a magnetic separatrix.
Experimental measurements have been made with Langmuir probes
and other diagnostics. Empirical seal ings of the scrape-off
layer parameters in terms of the main discharge parameters have
been established and compared with models of the scrape-off
layer. In this paper we review our understanding of Ohmic and
additionally heated, discharges in limiter and divertor
configurations.
1 Asociaci6n Euratom/CIEMAT, Madrid, Spain.
2 UKAEA Culham Laboratory, Abingdon, Oxfordshire, UK.
3 Central Institute of Electron Physics, Academy of Sciences, Berlin, GDR.
4 Institute for Aerospace Studies, University of Toronto, Toronto, Ontario, Canada.
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