Matlab-based Free-boundary Equilibrium Solver for Fast Control-oriented Predictions

X. Song, B. Leard, E. Schuster

Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)

Spokane, WA, USA, October 17-21, 2022

A free-boundary equilibrium solver for axisymmetric tokamak geometries has been developed based on the finite-difference and Picard-iteration methods in a rectangular computational area. The solver can run either in direct mode, where external coil currents are prescribed, or in indirect mode, where desired plasma boundaries with or without X points are prespecified to find the needed coil currents. The equilibrium solution is made consistent with nominal plasma parameters, such as the total plasma current (Ip), poloidal beta (bp) or safety factor (q) on a specified flux surface. To benchmark the mathematical correctness and accuracy of the solver, numerical solutions are compared to analytic fixed-boundary solutions. Furthermore, these numerical solutions are benchmarked against those produced by another numerical solver based on the finite-element and Newton-iteration methods in triangular grids. The equilibrium solver is being coupled with the Control Oriented Transport SIMulator (COTSIM) within a Matlab/Simulinkâ environment in its path to become a fast tokamak flight simulator enabling pulse design, model-based scenario optimization, and assessment of performance of control solutions in closed-loop simulations before experimental implementation.

*Supported by the US DOE under DE-SC0010537.