Integrated Modeling And Experimental Analysis Of Advanced Scenarios In Tokamak

Integrated modeling of tokamak plasmas is widely used in the predictive modeling of advanced scenarios and experimental analysis.In this work,modeling tools and code are used to pursue ways to high-performance scenarios in tokamaks,equilibrium reconstruction of tokamaks using diagnostic data,and analysis of experimental data based on the reconstructed results.Predictive integrated modeling of high-performance scenarios will help us deepen our understanding of the physical processes in highperformance scenarios and provide a theoretical basis for exploring better operation scenarios in the future.Meanwhile,it provides an improved direction for improving the confinement performance of the magnetic confinement plasma in the future experiments.Also,the processing and analysis of the experimental data can provide an important data basis for the follow-up study of the physical process in the experimentalplasmas,and in turn,provide an experimental basis for improving the simulation and prediction methods.Equilibrium reconstruction of tokamaks using diagnostic data is a key step.Improving the accuracy of reconstruction results has an important impact on the analysis of experimental data and the exploration of physical mechanisms.Edge localized current density profile in the advanced scenario is reconstructed from external magnetic data.Equilibrium reconstruction is important for the study of magnetically confined plasma in tokamaks,as well as for the integrated modeling and experimental analysis of advanced operation scenarios.It is crucial to obtain accurate internal plasma information by using highly accurate diagnostic data.In this work,by changing the current reconstruction algorithm in the equilibrium fitting code EFIT,edge-localized current information is obtained only using external magnetic diagnosis.Compared with the results of kinetic reconstruction,it is found that the results are in good agreement.Furthermore,the whole current profile is obtained by using the new algorithm combined with the external magnetic diagnosis data and MSE data.This indicates that the external magnetic diagnostic data can provide us the internal current information.As two kinds of relatively reliable diagnosis,external magnetic diagnosis and MSE diagnosis can extract whole current profile.Integrated modeling of advanced scenarios with strong reversed-shear in the EAST tokamak is firstly carried out.We used an iterative method to investigate the influence of off-axis electron cyclotron heating(ECH)and different electron density on the predicted profiles.It was found that high off-axis deposited ECH(p～0.5)is favorable to obtain strong reversed-shear q-profile and large-radius ITBs.Further analysis shows that when the off-axis electron cyclotron heating is 2 MW,if<ne>nG>0.7,the qprofile with reversed-shear and the large-radius ITB are predicted.It is found that the ITBs in the predicted profiles will gradually move toward the axis as the electron density decreases.This indicates that the electron density has a great influence on the position with ITBs.However,if the off-axis electron cyclotron heating is reduced to 1.5 MW,when<ne>nG is about 0.9,ITBs are obtained in the predicted profiles.However,when the density is reduced to<ne>nG～0.8,ITB also disappears in the obtained profile.This shows that the off-axis electron cyclotron heating also plays an important role in obtaining the predicted ITBs.Also,modeling efforts have been carried out to pursue ways to scenarios with localized reversed-shear on EAST.Simulation results show that on the basis of the predicted scenarios strong reversed-shear,if a small electron cyclotron heating is applied to the core region(near axis),the scenario with localized reversed-shear can be achieved,and large-radius ITBs can also be obtained.By scanning the centrally deposited electron cyclotron heating(ECH)power,it is found that if the centrally deposited electron cyclotron heating power is too large(greater than 0.15 MW),the electron temperature,ion temperature and electron density will peak significantly near the axis,and q-profile with localized reversed-shear and large-radius ITBs won’t be obtained.In addition,through simulation analysis,it is found that the formation of ITB in the predicted profile is mainly caused by the r q-profile with reversed-shea and the increase of Shrafranov shift.The equilibrium and profiles obtained from the reconstruction are used to investigated the formation and maintenance of the internal transport barrier(ITB)in EAST high βN experiments.The results show that higher heating power is required to obtain the internal transport barrier in the experiments with higher density.In addition,the experimental results show that the formation of internal transport barrier is related to the appearance of fishbone activities.Further simulation analysis shows that E×B shear flow plays a key role in the formation of internal transport barrier in the channel of ion temperature.In the experiment,the toroidal rotation increases at about 4 s,the ion temperature and the internal transport barrier are formed;The internal transport barrier disappear in the ion temperature(Ti-ITB)with the decrease of the toroidal rotation.However,the increase of toroidal rotation does not promote the formation of internal transport barriers of electron temperature and electron density.After the appearance of the fishbone activities,the internal transport barriers of electron temperature and electron density were also observed,and the formation of the fishbone activities was accompanied by the increase of the toroidal rotation,and the internal transport barriers of ion temperature were also formed.One possible reason is that the appearance of fishbone activities induces the formation of internal transport barrier.In the positive feedback process of ITB formation,the toroidal rotation gradually increases,and the internal transport barriers of electron temperature,electron density and ion temperature gradually increase to a steady state.