Five-Period Quasi-Isodynamics Stellarator Configurations with a High β

Abstract

Quasi-isodynamic stellarators (stellarators with a poloidal direction of the lines of the absolute value of the magnetic field B = const at the magnetic surfaces, where the centers of the “banana” trajectories of all trapped particles move over the magnetic surfaces) have many advantageous characteristics, such as good collisionless fast particle confinement, small neoclassical transport coefficients, and a bootstrap current that tends to zero. The limiting plasma pressure in quasi-isodynamic stellarators with a simple period structure decreases with decreasing number of periods. The implementation of compact quasi-isodynamic stellarators with high plasma pressure requires a significant decrease in the secondary dipole current (the Pfirsch–Schlüter current). Earlier, six-period quasi-isodynamic configurations were described, with a complex period structure, a significantly decreased dipole current, and a high limiting plasma pressure relative to the magnetic field pressure (〈β〉 ≈ 0.2). The aspect ratio A in these configurations was approximately 30. In stellarators of this type, the limiting plasma pressure shouldn’t decrease with decreasing number of periods. In this work, results are presented of the boundary optimization of a five-period quasi-isodynamic stellarator with a complicated period structure with 〈β〉 ≈ 0.2 and an aspect ratio А ≈ 23.