Study Of Recycling And Impurity Behavior In Long-Pulse H-mode Discharges In EAST Tokamak

The purpose of future tokamak devices(ITER,CFETR)is high-power long-pulse steady-state operations.Effectively controlling the recycling and impurity partials is a necessary for this purpose.The Experimental Advanced Superconducting Tokamak(EAST)is a fully superconducting magnetic confinement facility with ITER-like magnetic field configurations.Development and demonstration of high-power long-pulse plasma operations are the key issues of EAST.Physically understanding and effectively controlling the recycling and impurity partials are crucial for EAST to achieve high-performance long-pulse steady-state operations in metal wall condition.In this thesis,based on the EAST tokamak experimental platform,the boundary visible spectroscopy diagnostic and fast-ion loss diagnostic have been developed and a series of related experiments have been carried out.This work is helpful to understand the particle recycling and impurity behavior,and is also helpful to explore effective control methods of particle recycling and impurities which can provide solid technical bases for obtaining high-performance long-pulse steady-state operations.Boundary visible spectroscopy diagnosis can provide important data support for the study of long-pulse particle recycling and impurity behavior.In addition,some high-energy particles are lost in EAST high-power operation,which will cause stronger recycling and impurity.Therefore,the boundary visible spectroscopy diagnostic system and fast-ion loss diagnostic system have been developed on EAST.By measuring Da(Ha)spectral line and calculating the hydrogen-deuterium ratio to studying the process of boundary recycling.By measuring high-n Balmer series emission lines(D?,D?,D?,etc.)of romance and emission lines of impurities to studing the process of boundary recycling and impurities behavior in middle or high density operation conditions.In the fast-ion loss diagnostic,the high-speed camera is used to measure the gyro radius and the pitch angle of the lost fast-ion,and the PMTs is used to analyze the instability of lost fast-ion.Under these diagnoses,EAST discharge,especially long pulse discharge point,is studied.In the exploration of EAST long-pulse and high-confinement steady-state plasma discharges,it was found that graphite wall materials,lithium wall conditioning,plasma configuration optimization,triangular deformation enhancement,internal cryogenic pump,strike point optimization and divertor detachment can effectively reduce boundary recycling and impurity.With graphite wall materials,the effective ion charge and radiation of impurities are low,the recycling and impurities are also low.Under lithium conditioning,due to the strong gettering effect of lithium on carbon,oxygen and hydrogen impurities,which significantly reduces fuel recycling and impurity content,and as a result,the quality of plasma is improved.In the discharges of switching the configurations between USN and LSN,the heat load shared between the two target plates in the upper and lower divertors,thus reducing the damage of the wall caused by the accumulated interaction between plasma with the wall.Optimization of the strike point can improve the pumping capacity of internal cryogenic pump,enhance the particle removing ability and reduce the recycling process.In the medium and high-density discharges,plasma detachments were achieved which greatly reduces the damage of particles to the first wall and the formation of impurities.With these optimizations,EAST have been obtained high-confinement long-pulse steady-state plasma for about hundred seconds.It's well known that the accumulation of tungsten impurities in the core produces a large amount of radiation,which increases the radiation loss in the core plasma and reduces the plasma confinement performance.and put a limit in the realization of long-pulse steady-state H-mode discharges.Therefore,it is necessary to control both the source of boundary tungsten impurity and tungsten accumulation in the core effectively.The on-axis ECRH heating in EAST tokamak can effectively control the accumulation process of tungsten impurity in the core.The core ECRH heating is mainly heating electrons,which increases the electron temperature,enhances the anomalous transport process in the core,and then reduces the inward drift of the high Z impurity.A long-pulse H-mode discharge of 102s has been obtained by the optimization of all methods mentioned above.Based on the visible spectrum diagnostic and other diagnostics,the characteristics of particle recycling and impurity behavior in EAST are studied,and many effective methods for controlling recycling and impurity are explored.The work in this thesis are facing the high-power,steady-state operation of ITER and CFETR in the future,more research in controlling the recycling and impurities in the high-confinement long-pulse steady-state plasma are needed.