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Experimental study of the stability of Alfvén Eigenmodes on JET

Funded under: FP5-EAECTP C


Over the last few years, experiments have been performed on JET to study the dependence of the AE stability limits on the main plasma parameters in different operating scenarios. The measurements are compared with theoretical models, with the aim of improving the prediction capabilities for burning plasma experiments, such as ITER. An increase in the edge magnetic shear provides a significant stabilising contribution for AEs in plasmas characterised by a monotonic q-profile. Conversely, with non-monotonic q-profiles and Internal Transport Barriers, multiple weakly damped modes exist in the Alfvén frequency range even in the presence of a high edge magnetic shear, with possible negative implications for the AE stability in ITER. The dependence of the frequency and damping rate for n=1 TAEs on the bulk plasma Beta was also analysed using NBI heating in limiter plasmas. The mode frequency decreases for increasing Beta, in agreement with fluid and gyrokinetic predictions. Conversely, contrary to fluid predictions for intermediate and high-n TAEs, for low NBI powers we observe a splitting in the n=1 TAE frequency spectrum, accompanied by a reduction in the mode damping rate. The dependence of the damping rate for n=1 TAEs on the Larmor radius rho, has been investigated for plasmas characterized by a low magnetic shear in the core. In these plasma the coupling between AEs and kinetic Alfvén waves is predicted to contribute significantly to the total damping rate for n=1 TAEs. This mechanism is accounted for by the radiative damping model in the NOVA-K code.

Additional information

Authors: TESTA D, Plasma Science and Fusion Center, Massachusetts Institute of Technology, Boston (US);FASOLI A, Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne (CH);JAUN A, NADA VR-Euratom Association, Royal Instutute of Technology, Stockholm (SE);FU G, Princeton Plasma Physics Laboratory, Princeton (US);BORBA D, Associacão EURATOM/IST (PT);DE VRIES P, Association EURATOM - FOM Rijnhuizen, Nieuwegein (NL)
Bibliographic Reference: A paper presented at: 19th IAEA Fusion Energy Conference. Organised by: International Atomic Energy Agency (IAEA). Held at: Lyon, France, October 14-19 2002.
Availability: This paper is published in EPFL Internal Report LRP 738/02, available free of charge from: École Polytechnique Fédérale de Lausanne, Ecublens, CH-1015 Lausanne. Fax: +41-21-6934747.
Record Number: 200315846 / Last updated on: 2003-01-31
Original language: en
Available languages: en