Finite Beta Effects on Dynamic Ergodic Divertor

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In recent tokamak experiments, it is noted that stochastic field lines reduce strong heat load driven by the edge localize mode(ELM) to the divertor plate. Stochastic field lines are produced by the external perturbed field and it is called the Resonat Magnetic Perturbation(RMP) by Dynamic Ergodic Divertor(DED). From the viewpoint of high-βstellarator equilibrium, 3D effects on the DED field are very important because pressure-induced perturbed field makes further stochasticity of magnetic field lines in the peripheral region. However, in present analysis of RMP fields, a vacuum helical perturbed field superimposed on a 2D MHD equilibrium, a so-called vacuum approximation, is widely used. Since the vacuum approximation does not include the plasma response, considerations including the plasma response and its impact are critical and urgent issue.In this study, as a first step of 3D MHD modeling, the fully 3D MHD equilibrium of non-axisymmetric tokamak is solved numerically and equilibrium responses are studied. For this study, we use a 3D MHD equilibrium code HINT2, which is widely used to analyze the 3D equilibrium of helical system plasmas. Analyzing 3D MHD equilibrium, change of the magnetic topology was found. This does not appear in the vacuum approximation. This is an important point between the 3D MHD modeling and the vacuum approximation.