Study Of Edge Magnetic Topology Change Induced By3D Magnetic Perturbation On Tokamak

Magnetic confined fusion is one of the most popular way in controlled nuclear fusionresearches, which aims at providing inexhaustible and clean energy for human beings by makingpeaceful use of nuclear fusion. Many researches have shown that tokamak, a kind of torus magneticconfinement device, is outstanding and promising for achieving the goal. ITER program is a planof constructing an experimental reactor based on the ‘tokamak’ concept to explore long pulsedischarges and study the engineer and physical feasibility related to fusion reactors.The magnetic field in tokamak consists of two parts, the equilibrium field and perturbationfield. The former is a2D topology constructed by helix magnetic field lines on nested torus. Thelater usually comes from construction errors, stray fields from external systems and magneticperturbation coils. Resonant magnetic perturbation (RMP) coils are always used to generate radialmagnetic perturbations. It has been an effective methods for control of magnetohydrodynamics,especially for the ELM-control.The work of this paper is based on Experimental Advanced Superconducting Tokamak (EAST)in Institute of Plasma Physics of Chinese Academy of Science. A numerical modeling code usingfield line tracing algorithm named TOP2D is developed for modeling3D magnetic topology intokamaks. Modeling results show that magnetic island chains are formed on rational surfaces dueto RMPs. Near separatrix adjacent island chains overlaps to form a stochastic layer on plasmaboundary. The separatrix also splits to form multiple helical stripes on divertor targets. So field linesinside equilibrium separatrix which enter edge stochastic layer may connect to the divertor targets.The helical stripes formed by field line strike point splitting on divertor targets are called magneticfootprints. Both the stochastic layer width and splitting degree are found to be influenced by theresonance characteristics of perturbation spectrum.On EAST2014campaign, RMP experiments were operated and the magnetic topology changeswere observed by CCD cameras and divertor probes. It confirms the effect of RMPs and theusefulness of this numerical modeling code. In future EAST experiments, numerical modeling can provide more references and help to study the physical mechanisms related to edge transport processand controlling MHD instabilities along with experimental analyses. The RMP experiments onEAST will also provide credible data and technical experience for ITER program.