Contour Method for Resistive Evolution of Grad-Shafranov Plasma Equilibrium and Its Application to MTF Studies at General Fusion

We present a numerical code based on a contour method, which is developed at General Fusion (GF) for simulating magnetized plasma dynamics. The goal of this code is to model the existing GF plasma experiments and to guide the design of future GF magnetized target fusion (MTF) systems, in which metal liner compresses compact toroid plasma. The method assumes that the tokamak-like plasma goes through a sequence of axisymmetric Grad-Shafranov equilibria, which are linked together through the transport processes. The plasma is represented as a set of nested contours (flux surfaces), each of them encloses a fixed amount of plasma particles and corresponds to some values of poloidal flux Ψ_c, toroidal flux Φ_c and entropy S_c. The contours are reconstructed as levels of poloidal flux function Ψ(r,z) on 2D Eulerian quadrilateral mesh. At every time step, the code alternates between 1D transport sub-step, where updated values of Ψ_c, Φ_c and S_c are calculated using contour averaged transport equations, and 2D Grad-Shafranov sub-step, where new equilibrium mesh function Ψ(r,z) is found by iterations. The main advantage of this code is its speed: the time step is limited by a large resistive diffusion timescale and not by a small Alfven timescale as in usual MHD codes. The code can be generalized to include moving boundaries of plasma domain, which is especially useful in modeling MTF systems. Verification of our code against open source code MHD OpenFOAM and comparison of results with ongoing GF experiments will be demonstrated.