| The excessively high heat flux control is the critical task for tokamak long-pulse high-performance operation.For ITER,the steady-state heat flux must be exhausted from 40 MW/m2 to less than 15 MW/m2.During type-I ELM burst,the transient heat flux will reach around 10 MJ/m2 while the divertor target limit is only around 0.5 MJ/m2 For CFETR and future fusion reactor,the steady-state and transient heat fluxes will be much higher than the material limit.The past radiative divertor experiments in tokamaks have shown that the heat flux on the divertor target can be exhausted by ionization and radiation with impurity seeding from divertor region,such as N2,Ne and Ar.In this thesis,the detachment and grassy-ELM H mode have been combined in EAST to achieve the both control of steady-state and transient heat fluxes on the divertor target without significant confinement degradation.Firstly,the radiative divertor system has been upgraded.The piezo valves for the control of impurity seeding has been changed to the outside of the neck tubes in 2017-2018.In addition,a series of leak detection and test works have been performed to support radiative divertor physics and detachment feedback control experiments in 2018-2020 EAST campaigns.From 2020 to 2021,the EAST lower divertor has been upgraded to W divertor and the radiative divertor systems have also been upgraded.From 2016 to 2020,advanced research of surface eroding thermocouple(SETC)has been performed in order to measure the heat flux on the upgraded lower divetor target.The advanced research has shown the feasibility of surface eroding thermocouple in EAST.Secondly,the stable detachment with effective control of the steady-state heat flux on the divertor target has been achieved in EAST radiative divertor experiments.In recent EAST radiative divertor experiments with a favorable Bt direction(B × ▽B ↑)in the USN configuration,the partial energy detachment in the upper outer divertor has been achieved with either Ne or Ar seeding from upper outer divertor.The peak steady-state heat flux on the upper outer divertor target measured by probe was reduced by more than 70%,the Tet around upper outer strike point was reduced to around 5 eV and the C sputtering was well controlled.In relatively high performance H mode with Ip=550 kA and Pinj=3.7 MW,the peak steady-state heat flux on the upper outer divertor target was reduced from 4.6 MW/m2 to 2.5 MW/m2,by～45%with CD4 seeding.The Tet around upper outer strike point was reduced to less than 5 eV.In addition,a series of physics analyzations have been performed including the in-out asymmetry of divertor behavior in detachment process,comparison of radiation distribution with different Bt direction,and compatibility of detachment with core confinement.Thirdly,the steady-state and transient heat fluxes have been both well controlled through the combination of radiative divertor and grassy-ELM H mode.The experiments in EAST show that the unmitigated peak heat flux on the divertor target in grassy-ELM H mode is only 5-10%as compared with it in type-I ELM H-mode.Compared with type-III ELM H mode,the confinement of grassy-ELM H mode is much better.To reduce the steady-state and transient heat fluxes on the divertor target simultaneously,the experiment to combine the grassy-ELM H-mode and radiative divertor operation was proposed and performed in the 2018-2020 EAST campaign.The first stable deep particle detachment,and partial detachment without confinement degradation have both been achieved in the grassy-ELM H-mode.The comparison and analyzation have shown the compatibility of grassy-ELM H mode and radiative divertor.In addition,detachment feedback control experiments have also been performed in grassy-ELM H-mode.Through the newly developed detachment feedback control scheme,the upper outer divertor target was well protected without significant confinement degradation.Compared with original single Tet or radiation feedback control scheme,the new feedback control scheme is more suitable for long-pulse detachment feedback control.The combination of partial detachment and grassy-ELM H mode is one of the promising modes for EAST and fusion reactor long-pulse operation considering the core confinement,as well as the reduction of steady-state and transient heat flux on the divertor target.The first experiment research has been conducted in the thesis and the feasibility of combination of radiative divertor and grassy-ELM H-mode has been preliminarily confirmed in EAST,which can provide reference for fusion reactor operation.However,the operation parameters in EAST is far from them in fusion reactor.In the future,more radiative divertor experiments will be conducted with higher operation parameters. |
