Study Of The Physical Mechanism Of Edge Localized Mode Control Using Resonant Magnetic Perturbations Based On Plasma Response To Non-axisymmetric Magnetic Field

An investigation of plasma response to non-axisymmetric magnetic perturbations in tokamaks is carried out,which improves the understanding of the physical mechanism of edge localized mode(ELM)control using resonant magnetic perturbations(RMPs).The results suggest that plasma response to RMP is multi-modal,linear multi-mode plasma response can be used to optimize ELM control window,and non-linear plasma response is the key to understand the physical mechanism of ELM suppression.The contributions of this work are embodied in the following aspects.First,a system to measure the non-axisymmetric magnetic plasma response is established based on the EAST magnetic diagnostics,which provides the information of both toroidal and poloidal plasma response in experiments.Meanwhile,a new technique based on singular value decomposition for multi-mode plasma response extraction is presented,which extracts modes by separating the full poloidal cross-section structure from the phase difference between upper and lower RMP coils ??UL· Modes with physical meanings can be extracted with this technique,which helps to improve the understanding of 3D physics in tokamaks.Second,a systematic investigation of the property of linear plasma response in EAST is carried out,which demonstrates that plasma response in EAST is multi-modal.The ??UL dependence of plasma response shows good agreement between experiments and simulations in various beta and q95 operating regimes,which indicate single fluid model is capable of plasma response simulation in EAST current operating regime.Furthermore,with the new multi-mode technique,a detailed investigation of the multi-mode plasma response property is carried out.The amplitude of the dominant and secondary mode shows different space dependence,which suggests plasma response measured by magnetic sensors at different position have different dependence of q95.This is proved by experimental measurement,which further demonstrate the multi-modal feature of plasma response in EAST.Third,an investigation of the relation between multi-mode plasma response and ELM control is carried out,which shows that the mode with highest resonance on pedestal top is strongly correlated with ELM mitigation or suppression.The ??UL dependence of extracted modes are compared to the effect of ELM control using both n=2 and n=3 RMP in wide q95 operating regimes.It shows that the mode with highest resonant plasma response near the pedestal top is strongly correlated with ELM mitigation or suppression,even if the mode is not the dominant one in plasma response.These results demonstrate that multi-mode plasma response should be taken into consideration for ELM control,and the mode with more resonance on pedestal top plays key role in this process.Fourth,an investigation of ELM control using mixed toroidal harmonic RMPs is carried out in EAST/DIII-D international cooperation experiment,which demonstrates that edge components penetrate during the transition from ELM mitigation to suppression.It is observed that mixed toroidal harmonic RMPs lower the threshold current for ELM suppression compared to the single n=3 case.The decreased threshold suggests that mixed toroidal harmonic RMPs offers a better path to ELM control.The error field effect is studied by superimposing n=2 error field correction upon the n=2 phase scan,which shows that it is possible to suppress ELM and correct error field simultaneously.The plasma response measured by magnetic sensors shows the n= 3 harmonic plays the key role in ELM suppression using mixed toroidal harmonic RMPs.Simulations using toroidal rotation find good agreement with the ELM mitigated phase when the input rotation profile is high and induces strong screening of the RMP.Simulations with zero-crossing rotation find strong penetration of the RMP and reproduce the mode structure of ELM suppression on both the low and high field side.This suggests that edge components may penetrate during the transition from ELM mitigation to suppression.This work improves the understanding of ELM control related 3D physics,and further demonstrate that 3D coils can be used to improve plasma confinement and stability in tokamaks.This can be used to optimize operation scenario for ITER and future fusion reactor,and improves the economic efficiency and practicability of them.