Numerical Calculation Of The Plasma Equilibrium And Influence Of Magnetic Perturbation On Runaway Current On J-TEXT

It is very important to obtain reliable and accurate plasma discharge configuration and related discharge parameters during the tokamak discharge.Grad-Shafranov equilibrium equation is derived,analytic solution is obtained by using the separation variable method combining with the EFIT（equilibrium fitting code）algorithm and related diagnostic data（such as SXR-soft X ray emission data computing magnetic axis location and magnetic probe data,etc.）to determine the optimal solution,then obtain the distribution of current density profile,pressure profile,safety factor profile,the magnetic surface profile.The thermal deposition,electromagnetic stress and runaway electrons can severely threaten the safe operation of tokamak during disruption,the main research is how to avoid or suppress runaway current.Different devices have done a lot of experiment about magnetic perturbation suppressing runaway electrons.The experiment results show that the magnetic perturbation within a certain range can suppress the runaway current,when magnetic perturbation is too large,the escape current can increase instead in J-TEXT tokamak.In this paper,the influence of different magnetic perturbations on the runaway current are studied by numerical calculation.The study shows:when the magnetic perturbation valueδB/B is in the range of 0¹0^-3,the runaway current decreases with the increase of magnetic perturbation value.During pre-disruption（plasma discharge current platform）,the current density profile from the core to the edge of change is flat.During plasma disruption without magnetic perturbation（runaway current platform）,current density profile is steep.When magnetic perturbationδB/B<10^-4,core current density peak is not obvious,but there is still a certain peak tendency.When magnetic perturbationδB/B>10^-4,the current density peak trend will increase increasing with the magnetic perturbation value increasing.Therefore,the magnetic perturbation will be able to suppress the runaway current within the range of deltaδB/B=10^-4.Based on the J-TEXT tokamak device,the pulse height analyzer diagnosis system is built,it is used to measure the core plasma temperature and the behavior of mid-high Z impurities.Electron temperature can reflect a lot of physical phenomena,such as plasma MHD（magneto-hydro dynamic）behavior.The spectrum measurement of equilibrium plasma is obtained via different discharge conditions:when the plasma discharge current is larger,the electron density is higher,the core plasma temperature is much higher.When the positive EB（electrode biasing）is added,the radiation of Hαdecreases,the plasma confinement is improved,and the core temperature increases.With the external RMP（Resonant magnetic perturbation）,the plasma penetrates,the plasma confinement becomes poor and the core temperature decreases.During plasma discharge,these high Z material impurities will inevitably exist in plasma and can influence the plasma discharge behavior because of their larger dilution and radiation energy loss characteristics.In this paper,we study the behavior of high Z impurity in the core plasma by using the PHA diagnosis system in J-TEXT tokamak.Due to the Kαline emission energy characteristic,the high Z impurities appear in the J-TEXT tokamak plasma mainly include Ar,Cr and Fe.The results show:the plasma density is lower,the impurity radiation is much higher;when the positive EB is added,Cr and Fe impurity radiation decreases;when the external RMP（resonant magnetic perturbation）is added,the plasma penetrates,the plasma temperature decreases,and the radiation intensity of Ar impurity decreases continuously.