Abstract
The NSTAB nonlinear stability code solves differential equations in conservation form, and the TRAN Monte Carlo test particle code tracks guiding center orbits in a fixed background, to provide simulations of equilibrium, stability, and transport in tokamaks and stellarators. These codes are well correlated with experimental observations and have been validated by convergence studies. Bifurcated 3D solutions of the 2D tokamak problem have been calculated that model persistent disruptions, neoclassical tearing modes (NTMs) and edge localized modes (ELMs) occurring in the International Thermonuclear Experimental Reactor (ITER), which does not pass the NSTAB simulation test for nonlinear stability. So we have designed a quasiaxially symmetric (QAS) stellarator with similar proportions as a candidate for the demonstration (DEMO) fusion reactor that does pass the test [1]. The configuration has two field periods and an exceptionally accurate 2D symmetry that furnishes excellent thermal confinement and good control of the prompt loss of alpha particles. Robust coils are found from a filtered form of the Biot-Savart law based on a distribution of current over a control surface for the coils and the current in the plasma defined by the equilibrium calculation. Computational science has addressed the issues of equilibrium, stability, and transport, so it remains to develop an effective plan to construct the coils and build a diverter.
Highlights
The NSTAB nonlinear stability code solves differential equations in conservation form, and the TRAN Monte Carlo test particle code tracks guiding center orbits in a fixed background, to provide simulations of equilibrium, stability, and transport in tokamaks and stellarators
Computer Simulation of Magnetic Fusion. Comparisons with both theory and experiment have shown that the NSTAB simulation of magnetic fusion in three dimensions gives reliable predictions of what can be expected to happen in practice
The results of computational science show that the best resolution of these issues will be a switch to quasiaxially symmetric (QAS) or quasihelically symmetric (QHS) stellarators in the search for good candidates
Summary
Comparisons with both theory and experiment have shown that the NSTAB simulation of magnetic fusion in three dimensions gives reliable predictions of what can be expected to happen in practice. This configuration is MHD stable for realistic changes in the shape of the plasma. The NSTAB simulation of magnetic fusion predicts poor performance of ITER, but it shows that a QAS stellarator with comparable specifications would be a good reactor. An experimental verification that the required superconducting coils and magnets can be constructed and supported remains an open question in nuclear engineering. The discovery of QAS and QHS configurations has brought us to a turning point in magnetic fusion research that makes successful solutions of the problems with equilibrium, stability, and transport inside the plasma tractable. A useful project would be to study questions of mechanical and nuclear engineering that arise in the construction of magnets and modular coils
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