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(EXP5/14) Results from Transient Transport Experiments in Rijnhuizen Tokamak Project: Heat Convection, Transport Barriers and `Non-local' Effects

P. Mantica¹⁾, G. Gorini¹⁾²⁾, G. M. D. Hogeweij³⁾, J. de Kloe³⁾, N. J. Lopes Cardozo³⁾, A. M. R. Schilham^3)
 
1) Istituto di Fisica del Plasma `P.Caldirola', Associazione Euratom-ENEA-CNR, Milano, Italy
<sup>2)</sup> INFM and Dipartimento di Fisica `G.Occhialini', Universitá degli Studi di Milano-Bicocca, Milano, Italy
³⁾ FOM Instituut voor Plasmafysica `Rijnhuizen', Associatie Euratom-FOM, Trilateral Euregio Cluster, 3430 BE Nieuwegein, The Netherlands

Abstract.  An overview of experimental transport studies performed on the Rijnhuizen Tokamak Project (RTP) using transient transport techniques in both Ohmic and ECH dominated plasmas is presented. Modulated Electron Cyclotron Heating (ECH) and oblique pellet injection (OPI) have been used to induce electron temperature ( T_e) perturbations at different radial locations. These were used to probe the electron transport barriers observed near low order rational magnetic surfaces in ECH dominated steady-state RTP plasmas. Layers of inward electron heat convection in off-axis ECH plasmas were detected with modulated ECH. This suggests that RTP electron transport barriers consist of heat pinch layers rather than layers of low thermal diffusivity. In a different set of experiments, OPI triggered a transient rise of the core T_e due to an increase of the T_e gradient in the 1 < q < 2 region. These transient transport barriers were probed with modulated ECH and found to be due to a transient drop of the electron heat diffusivity, except for off-axis ECH plasmas, where a transient inward pinch is also observed. Transient transport studies in RTP could not solve this puzzling interplay between heat diffusion and convection in determining an electron transport barrier. They nevertheless provided challenging experimental evidence both for theoretical modelling and for future experiments.

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