Experimental Study On Divertor Heat Flux Under Resonant Magnetic Perturbations In EAST

The extremely high heat flux on divertor component is one of the key problems to be solved in the steady-state operation of magnetic confinement fusion reactor under high confinement mode（H-mode）.During H-mode operations,the divertor suffers from not only the severe stationary heat flux,but also huge transient heat flux caused by edge-localized modes（ELMs）.Resonant magnetic perturbation（RMP）is an effective method for controlling ELMs,while also modifying the deposition of stationary heat flux on the divertor by changing the magnetic topology in tokamak.Understanding the deposition pattern of divertor heat flux under RMP will provide a scientific basis for effectively control of the severe heat flux.Basing on the fully superconducting tokamak EAST and the wide-angle infrared diagnostic system,this thesis presents a systematic experimental study on divertor heat flux under RMP.The work content and results are as follows:The previous infrared diagnostic system is limited in the field of view.In order to achieve full monitoring coverage of crucial plasma-facing components（PFCs）in EAST,as well as to improve the viewing range of the divertor,the wide-angle infrared diagnostic system has been upgraded.This work aims to support the long-pulse and high-parameter plasma operations in EAST,while also provides a diagnostic foundation for researching divertor heat flux.To solve the problem of inevitable jitters on infrared images during plasma discharge,an algorithm based on phase correlation of image edges has been developed to correct the jitters in the infrared video.This correction ensures the data quality of the infrared diagnostic and significantly improves the accuracy of heat flux calculation,providing a technical foundation for divertor heat flux research in EAST.Based on experiments and theoretical simulations,the dependence of divertor heat flux characteristics on basic RMP parameters was studied and clarified.The experiment shows that there exists a threshold in RMP coil current for inducing the strike point splitting.Observations indicate that the heat flux amplitude at the secondary strike point increases with RMP coil current.Theoretical simulations suggest that this is due to a deeper penetration of magnetic field lines under higher coil current.The RMP phase scanning makes the splitting structures of heat flux scan on the target plate.This phenomenon can be qualitatively explained by magnetic footprint simulations.However,analysis shows that the heat flux structure scanning induced by phase scanning does not effectively improve the heat flux distribution.It is found that even under the upper single null（USN）configuration,RMP can cause magnetic connection to the lower outer divertor（LO-div）by modifying the magnetic topology and then transport the heat from the plasma to LO-div.By using the upgraded infrared diagnostic system,for the first time,the toroidal asymmetry of divertor heat deposition under RMPs with different toroidal mode numbers was directly observed in EAST.The experimental results show that RMP with higher toroidal mode number can induce finer splitting structures.The results are in good agreement with the theoretical simulations.Besides,we conducted the experimental investigation into toroidal homogenization of divertor heat flux using RMP rotation.The results show that the broadening factor of divertor heat flux is improved and the peak heat flux is reduced after hornogenization,and larger RMP coil current leads to better homogenization.The systematic studies were also conducted to investigate the divertor heat flux characteristics under RMP suppressing ELMs.The experiments revealed that there are shifting in the heat flux splitting structure and in the allocation of heat flux between inner and outer target plate,during the transition from ELM mitigation to ELM suppression.The averaged heat flux profiles of ELM mitigation and ELM suppression were compared and analyzed by means of high-frequency infrared diagnostics to verify the energy balance of heat deposition while ELM mitigation and ELM suppression.The divertor heat flux under compatibility of ELM suppression with gas puffing and pellet injection was also studied.It was demonstrated that increasing the plasma density with gas puffing while maintaining complete ELM suppression.Under the synergy of RMP and gas puffing,the heat flux allocation between inner and outer target plates is optimized and the peak heat flux on outer target plate is effectively mitigated.Pellet injection under RMP resulted in an effective increase in plasma density and a decrease in divertor heat flux,but at the cost of decreased plasma temperature and worse ELM control conditions.By scanning the discrepancy of the lower and upper separatrix radii mapped to the LFS mid-plane(dR_sep)in the USN configuration.it was found that RMP is possible to maintain good ELM control within a certain range of dR_sep without inducing additional strike points to LO-div.