Studies of divertor magnetic configurations and control systems for fusion energy experiments

Abstract

The divertor is one of the most essential components in tokamaks and sustaining the excessive heat power strike. The sputtered impurity particles from the damaged divertor surface materials can dilute and contaminate the plasma, degrading the confinement and fusion efficiency. Thus, the divertor overheating has been one of the most challengeable issues for the fusion reactors like ITER. The divertor heat load is determined by the edge plasma parameters. Using the edge transport code can help us to explore the available way to generate the detached plasma. We used the transport code SOLEDGE2D-EIRENE to simulate the radiative divertor plasma and the quasi-snowflake (QSF) plasma on EAST. SOLEDGE2D-EIRENE is a typical 2-D fluid code of the edge plasma by solving Braginskii equations with the Bohm boundary conditions. Modeling result indicates that the neon seeding increased the radiated power both in the plasma core and the divertor region, and the mitigation of the divertor heat load still can be improved. The QSF magnetic configuration is a special advanced divertor shape on EAST which is similar to snowflake minus(SF-) configuration. Longer poloidal connection length of the scrape-off layer(SOL) of QSF plasma increases the radiated power loss compared with the normal single null(SN) configuration, which is beneficial for reducing the divertor heat load. The detachment feedback control is also developed on EAST. We firstly used the CD4 as the working gas to realize the divertor electron temperature (Te,div) feedback control. CD4 shows a different physical mechanism of forming detachment compared to the medium Z impurity like neon(Ne) and argon(Ar). The integrated control method of Te div-Prad joint feedback was achieved in H-mode plasma: Prad feedback control increases the radiated power, while Te,div monitor judges the divertor detached situation. Through this way, the robustness of the feedback control system is improved, using less impurity seeding amount still can keep the detachment and having less influence on the core confinement.