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Understanding of the
shape, electron heat
internal transport barriers
ASDEX Upgrade |
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A.G. Peeters, C. Angioni, M. Apostoliceanu, G.V. Pereverzev,
E. Quigley, F. Ryter, D. Strintzi, F. Jenko, U. Fahrbach, C. Fuchs,
O. Gehre, J. Hobirk, B. Kurzan, C.F. Maggi, A. Manini,
P.J. McCarthy, H. Meister, J. Schweinzer, J. Stober, W. Suttrop,
G. Tardini and the ASDEX Upgrade Team |
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2005 |
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DOI |
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Resumo |
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In this paper several transport phenomena are described and explained through a (quasi) linear description of
the micro-instabilities. This paper deals with the following phenomena: density peaking, electron heat transport,
density pump-out, reactor density profiles and the stabilization of the ion temperature gradient (ITG) mode in
transport barriers. Density peaking is observed to increase with decreasing collisionality—a phenomenon that can
be explained by the influence of collisions on the trapped electron response. The density pump-out due to central
electron heating is observed to occur only if the dominant instability is the trapped electron mode (TEM). The
proposed explanation involves the thermo-diffusive contribution to the particle flux which is outwards for the TEM
while it is inwards for the ITG. The insight in the density profile behaviour can be used to predict moderately peaked
density profiles in a reactor. Collisionality is also found to influence the electron heat flux in discharges with dominant
electron heating even at relatively small values of the density. The dominant instability under dominant electron
heating is found to be the TEM, and the dependence of the electron heat flux on the electron temperature gradient is
reasonably described by the quasi-linear results. At higher density (and collisionality) the growth rate of the TEM
is reduced and a transition to a dominant ITG is found. This transition is reflected in the speed of the electron heat
pulse propagation. Finally, it has been found that the ITG under experimentally relevant conditions is not stabilized
by a uniform radial electric field. |
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