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(EX/C4-2Ra) Electron Heat Transport in ASDEX Upgrade: Experiment and Modelling

F. Ryter¹⁾, G. Tardini¹⁾, F. De Luca⁴⁾, H.-U. Fahrbach¹⁾, F. Imbeaux²⁾, A. Jacchia³⁾, K.K. Kirov¹⁾, F. Leuterer¹⁾, P. Mantica³⁾, A.G. Peeters¹⁾, G. Pereverzev¹⁾, W. Suttrop¹⁾, ASDEX Upgrade Team^1)
 
1) IPP-Garching, Garching, Germany
²⁾ DRFC, Association Euratom-CEA, CEA-Cadarache, France
³⁾ Istituto di Fisica del Plasma, Associazione EURATOM-ENEA-CNR, Milano, Italy
⁴⁾ INFM and Dipartemento di Fisica, Universita degli Studi di Milano, Milano, Italy

Abstract.  The temperature profile resilience observed in tokamak conventional plasmas has been clearly attributed to a threshold in inverse gradient length: above this threshold transport increases strongly whereas it is very low below. New experiments with ECH in ASDEX Upgrade allow to determine the threshold by varying the heat flux in the confinement region by one of magnitude while keeping the plasma boundary constant. Such experiments at low density with pure electron heating allow to study in detail the electron heat transport. In addition the influence of ion heat flux and coupling between the species is studied. The experimental result are compared with the ITG/TEM Weiland model which shows excellent agreement. The results on threshold seem to support the hypothesis that TEM rather than ETG turbulence is the dominant cause of anomalous electron heat transport. In these experiments power modulation of ECH allow simultaneously the investigation of transient transport which is also well reproduced by the Weiland model. Therefore a single physics-based transport model including ITG/TEM physics reproduces the experimental heat transport results under quite different conditions.

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