Effect Of The Limiter Biasing On The Impurity Behavior In Edge Region Of J-TEXT Tokamak

The impurity in fusion plasma may increase the plasma radiation and decrease the core temperature,hence affect the MHD stability.Furthermore,it can also dilute the fusion fuels and reduce the efficiency of the fusion reaction.Therefore,impurity control is the key to the stable operation of fusion reactors in the future.The concentration of impurities in tokamak plasma is mainly dominated by impurity transport in the core region and the impurity source from the edge region.Varying the relative potential between the limiter and the plasma is supposed to be able to modulate the plasma-limiter interaction process,change the pattern of plasma flow,and affect the impurity generation and transport in the edge region afterward.This thesis based on the study of the effect of limiter biasing on plasma parameters and impurity radiation to explore the possibilities of impurity control on J-TEXT tokamak.In order to study the behavior of edge impurities,several spectroscopic diagnostic systems have been developed on J-TEXT tokamak.And a new vacuum ultraviolet(VUV)spectroscopy system has been established.In this thesis,the calibration and upgrade of the VUV system are completed.The study of the effect of limiter biasing on impurity behavior is carried out based on the above-mentioned diagnostics.The five points will be discussed.Firstly,an alignment plate customized with different shaped apertures is designed for the optical alignment.Secondly,based on the spectral lines of carbon III(97.7nm,229.7nm and 465nm),carbon IV(154.8nm and 580nm),carbon V(227.1nm)and oxygen V(278.1nm and 283.6nm),the absolute sensitivity calibration is accomplished via collisional radiation ratio,ADAS database,and STRAHL code.Thirdly,by replacing the previous CCD of the VUV system with the microchannel plate(MCP)equipped with an Electron Multiplying Charge Coupled Device(EMCCD),the temporal resolution of the VUV system has been upgraded to 2ms from 30 ms.Fourthly,it is foundthat the positive biasing on the top limiter is more effective to improve the plasma particle confinement.Fifthly,it is found that the positive biasing on the low-field limiter may be more effective in enhancing the edge impurity screening and reducing the core impurity concentration.