Fast-ion transport induced by externally applied Resonant Magnetic Perturbations in the ASDEX Upgrade tokamak

Description

In magnetically con ned fusion plasmas, MHD instabilities such as the Edge Localized Modes (ELMs), present in current devices, need to be kept under control in order to avoid too high heat uxes on plasma facing components. Therefore, substantial e orts have been focused on developing techniques to mitigate these instabilities. Among these methods, one of the most promising techniques is the application of external Magnetic Perturbations (MPs), which have been observed to e ectively mitigate or even suppress ELM instabilities. However, the inclusion of a 3D perturbative eld has a strong impact on the plasma stability and con nement. Fast-ions (i.e. supra-thermal ions) resulting from the fusion device plasma heating systems and fusion reactions require a good con nement to preserve the device performance and integrity. Therefore, the study of the impact that perturbative elds have on energetic particles is crucial to assess and design the MPs systems in future machines like ITER. In this thesis, dedicated experiments in AUG have been carried out to analyse the fast-ion transport dependence on the poloidal spectra of the perturbation, showing that the amplitude of the observed fast-ion losses depends strongly on the energetic particle phase space and poloidal mode spectra of the external perturbation. The transport mechanism underlying these experimental results has been analysed through realistic numerical simulations using the ASCOT code. The results of these simulations have been combined with an analytical theory of nonlinear wave-particle resonances. This has shown that the combination of multiple linear and nonlinear resonances with the applied perturbative elds create a region where resonant transport is maximised. This transport occurs at the plasma edge and depends on the perturbation poloidal and toroidal spectra, as well as the magnetic equilibrium and particle orbit topology. The impact of the collisionality and the radial electric elds on these resonances has also been assessed throughout this work. This analysis contributes to the ability to control the resonant transport at the plasma edge, which opens new avenues for the control of the energetic particle population and associated MHD uctuations in future burning plasmas.

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