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(EX/P1-17) Experimental Study of the Stability of Alfvén Eigenmodes on JET.

D. Testa¹⁾, A. Fasoli²⁾¹⁾, G. Fu⁴⁾, A. Jaun³⁾, D. Borba⁵⁾, P. de Vries⁶⁾, JET EFDA Contributors
 
¹⁾ Plasma Science and Fusion Center, Massachusetts Institute of Technology, Boston, USA
²⁾ CRPP, Association EURATOM – Confédération Suisse, EPFL, Lausanne, Switzerland
³⁾ NADA VR – Euratom Association, Royal Institute of Technology, Stockholm, Sweden
⁴⁾ Princeton Plasma Physics Laboratory, Princeton, New Jersey, USA
⁵⁾ Associacão EURATOM/IST, Portugal; EDFA – CSU, Culham Science Centre, UK
⁶⁾ Association EURATOM FOM – Rijnhuizen, TEC, Nieuwegein, NL

Abstract.  Over the last few years, experiments have been performed on JET to study the dependence of the AE stability limits on the plasma parameters in different operating scenarios. These measurements have been systematically compared with theoretical models, with the aim of providing accurate predictions for burning plasma experiments, such as ITER. The increase in the edge magnetic shear provides a significant stabilizing contribution for low-n AEs in plasmas characterized by a monotonic q-profile, in agreement with code predictions. Conversely, in plasmas characterized by a non-monotonic q-profile and an Internal Transport Barrier, we have observed for the first time multiple weakly damped modes in the Alfvén frequency range even in the presence of a high edge magnetic shear. The increase in core toroidal rotation and bulk plasma beta splits the n=1 TAE frequency spectrum, contributing to reduce the mode damping rate without fast ion drive. The dependence of the damping rate for n=1 TAEs on the normalized Larmor radius rhostar has been investigated: it was found that them damping rate does not depend on $\rho^{\ast}$ up to $\rho^{\ast}$ < 3.5×10^{- 3}, and then decreases at higher $\rho^{\ast}$.

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