Destabilization of Alfvénic activity by non-axisymmetric magnetic field induced rotation braking in KSTAR tokamak

Abstract

We report an experimental observation of destabilization of the Alfvénic activity by non-axisymmetric (3D) magnetic field induced toroidal rotation braking in the KSTAR tokamak. The toroidicity-induced Alfvén eigenmodes (TAEs) are destabilized when toroidal plasma rotation is reduced down to the minimum to approach near-zero rotational shear by 3D magnetic braking. This observation indicates that the stability of the TAEs is strongly correlated to the plasma rotation that modifies Alfvén continuum. The TAE frequency predicted by stability calculation with the reduced rotation is in a good agreement with the experimental measurement. It is suggested that the impact of 3D magnetic field and rotation on the Alfvénic modes and associated fast ion confinement should be considered for the operation of magnetic confinement fusion devices.

Non-linear MHD modelling of edge localized modes suppression by resonant magnetic perturbations in ITER

“…Considering that the physics of RMPs is still far from being fully understood, the most important question however remains at what conditions ELMs are suppressed in present day machines and will they be suppressed in ITER scenarios? Recent modelling results of RMP experiments in ASDEX-Upgrade [26] and KSTAR [31] validated many aspects of the RMPs and ELMs physics models implemented in the nonlinear resistive MHD JOREK code that we also used to model ELM suppression in ITER in this paper. It was demonstrated previously [19,26,31] that the non-linear multi-harmonics MHD approach, including a realistic tokamak geometry with the X-point and the scrape-off-layer (SOL), realistic geometry and spectrum of RMP coils, toroidal rotation, bi-fluid diamagnetic effects and neoclassical poloidal friction represent a minimum model which permits to reproduce experimental results of ELM suppression in modelling.…”

“…Recent modelling results of RMP experiments in ASDEX-Upgrade [26] and KSTAR [31] validated many aspects of the RMPs and ELMs physics models implemented in the nonlinear resistive MHD JOREK code that we also used to model ELM suppression in ITER in this paper. It was demonstrated previously [19,26,31] that the non-linear multi-harmonics MHD approach, including a realistic tokamak geometry with the X-point and the scrape-off-layer (SOL), realistic geometry and spectrum of RMP coils, toroidal rotation, bi-fluid diamagnetic effects and neoclassical poloidal friction represent a minimum model which permits to reproduce experimental results of ELM suppression in modelling. As it was shown in [19,26,31] RMPs drive non-linearly coupled side harmonics k × N locked to the static RMP with main toroidal number N in the ELM suppression stage while strongly mitigating other harmonics responsible for ELM crash.…”

“…In the present work the 3D non-linear resistive MHD code JOREK [42,43] was used taking into account two fluid (for electrons and ions) diamagnetic effects, neoclassical poloidal friction and toroidal rotation in realistic ITER geometry including X-point, SOL and divertor and realistic RMP coils geometry and spectrum. The reduced MHD model was previously described and validated in modelling of ELM suppression experiments using RMPs in AUG [26] and KSTAR [31].…”

“…It was demonstrated previously [19,26,31] that the non-linear multi-harmonics MHD approach, including a realistic tokamak geometry with the X-point and the scrape-off-layer (SOL), realistic geometry and spectrum of RMP coils, toroidal rotation, bi-fluid diamagnetic effects and neoclassical poloidal friction represent a minimum model which permits to reproduce experimental results of ELM suppression in modelling. As it was shown in [19,26,31] RMPs drive non-linearly coupled side harmonics k × N locked to the static RMP with main toroidal number N in the ELM suppression stage while strongly mitigating other harmonics responsible for ELM crash. It was shown that ELM are suppressed not only because of the reduction of the pressure gradient resulting from the heat and particle transport due to RMPs, but mainly due to these continuous MHD transport generated non-linearly [19,26].…”

“…In the present work, we adopted the different strategy to model RMPs using the 3D non-linear resistive MHD code JOREK which allows to calculate ELMs and RMP with self-consistent plasma response while taking into account two fluid diamagnetic effects, neoclassical poloidal friction and toroidal rotation in realistic ITER geometry including X-point, SOL and divertor. The model has previously been tested and validated on AUG and KSTAR RMP experiments [26,31]. Such approach gives a more correct magnetic 3D topology and edge transport due to RMPs.…”