Experimental And Simulation Studies Of Ne And Ar Seeded Radiative Divertor Plasma On EAST

The tokamak device is an important device to achieve magnetic confinement nuclear fusion.With the higher power in the tokamak,power exhaust problem will be one of the most critical issues for achieving nuclear fusion because the heat flux from the upstream plasma onto the divertor targets will exceed the maximum capability of the divertor targets.Seeding the noble extrinsic impurities to increase the radiation in divertor and Scrape-Off Layer(SOL)regions through ionizations and charge exchanges of the impurity particles,namely realizing the radiative divertor plasma operation,can effectively mitigating high particle and heat fluxes on divertor targets.In this thesis,neon(Ne)and argon(Ar)seeded radiative divertor plasmas are systematically investigated through both experimental and simulation methods on Experimental Advanced Superconducting Tokamak(EAST).The results in this dissertation could provide experiences and references for achieving EAST long-pulse high-performance operations and radiative divertor operations in future devices,such as ITER and CFETR.The theories and models related to the radiative divertor plasmas are introduced in the first part of this dissertation.Mechanism of the radiation divertor plasma involves complex processes of atomic,molecular and plasma physics.The simple one-dimensional model "two-point model" and plasma sheath theory can help us understand plasma states and detachment process.Anomalous transport theory explains radial transport in edge plasma,which is also beneficial to understand simulation model of SOLPS(Scrape-Off Layer Plasma Simulation).Behaviors of the radiation are also briefly introduced,which play key roles in the power exhaust process.Divertor gas puff system was upgraded since EAST upgraded its top divertor into ITER-like divertor in 2014,and the delay of injecting gas to divertor region was reduced significantly.Series of Ne and Ar seeded radiative divertor experiments were carried out under the new divertor condition.In Ne seeded radiative divertor experiments,Ne/D2 mixture with different proportions were seeded from the divertor region as the radiators to compare their different behaviors of detachment,heat flux reduction and physical sputtering on the targets.Different gas puff methods are also investigated.Using multi-pulse method can effectively avoid excessive impurities entering the plasma core region and causing contamination there.However,this method is less effective in achieving detachment.Based on experiences of different proportions and different injection methods,the radiation feedback control experiment and the detachment feedback control experiment were carried out respectively.The experiment successfully realized the feedback control of the total radiant power and the electron temperature near the strike point on the target.The detached plasma can be efficiently obtained while avoiding excessive impurities entering the plasma core.Similar researches in Ar seeded plasma were also carried out.The results show that the injection of Ar impurity can also effectively achieve the detached plasma,but the stricter requirements are imposed on the total amount of injected Ar.Excessive Ar gases are easier to cause significant power losses in the core region.At the same tim e,the Ar impurity could cause sever sputtering on the targets.This sputtering caused by Ar can be partially suppressed only when achieving the detachment.Comparisons between Ne and Ar seeding experiments are also discussed.To validate the experiment,fill the gap of the diagnostic data,and better understand the mechanism and physics of experiments,SOLPS-ITER numerical simulations are introduced in the studies of radiative divertor plasmas.Firstly,the validated simulations of the Ne and Ar seeded radiative divertor plasma are discussed.The simulation results are consistent with the experimental measurements.In addition to,based on the good agreements between experiments and descriptive simulations,predictive simulations of Ne-seeded plasma with different impurity seeding rates are also studied in this dissertation.These results will provide important references for the experiments in the future.