Confinement Simulation of Optimized Stellarators

Predicting the plasma energy and particle confinement and accessible ion temperature is a key challenge for understanding and designing optimized stellarator experiments and future fusion systems. The ion temperature which controls the fusion reaction is typically determined by marginal stability to the ITG critical gradient. Magnetic shaping of optimized stellarator equilibria has been shown to produce a wide variation of the ITG critical gradient by approximately a factor of 10 [1]. The impact of this variation on the predicted energy confinement and plasma temperature is assessed using the turbulent transport simulation code TRINITY3D. It solves the plasma transport equations using GX to simulate turbulent transport using delta-f flux-tube methods, KNOSOS to evaluation neoclassical transport, and simulations of plasma heating, particle sources, and losses. The plasma confinement and profiles are predicted for several optimized stellarator equilibria with high and low ITG critical gradients, and variations in shear. The results are analyzed to understand correlations. The variation of the predicted confinement with respect to magnetic field, plasma size, heating power, and plasma boundary conditions are compared with empirical confinement scaling. This will provide an initial evaluation of the range of optimized stellarator confinement that is accessible by design.

[1] G.T. Roberg-Clark, et al., 2023 Phys. Rev. Res. 5, L032030.