A Data-Assimilation Based Method for Equilibrium Reconstruction of Magnetic Fusion Plasma and its Application to Reversed Field Pinch

Carbon-free energy sources are essential to avoid global warming, and nuclear fusion is expected to play a major role in achieving clean and sustainable energy. In the development of magnetic fusion, there exist a lot of issues related with plasma equilibrium to be studied extensively, typical representative of which is a problem of equilibrium reconstruction of plasma. In this paper we propose a new method of equilibrium reconstruction for fusion plasma based on the data assimilation. Aiming at dealing not only with axisymmetric toroidal plasmas but also with more general toroidal plasmas, we formulate the problems of equilibrium reconstruction in generalized forms and derive methods to solve them. We also propose a method for applying the equilibrium reconstruction method to the reversed field pinch (RFP), and it is applied to a real RFP experimental apparatus for its evaluation. It is shown through numerical experiments that the proposed equilibrium reconstruction method works well with reasonable accuracy. And it is also shown through real experiments applying the RFP apparatus that the equilibrium of RFP plasma is appropriately reconstructed.