Fast particle optimization of a quasi-axisymmetric stellarator equilibrium using the Γ_C metric

An important goal of stellarator optimization is improvement of the confinement of fast particles, such as alpha particles created by DT fusion reactions. In this work, a fixed-boundary, quasi-axisymmetric (QA) stellarator equilibrium was re-optimized using the method outlined in Bader et al—minimization of both deviation from quasisymmetry as well as the analytical quantity Γ_C, the latter of which represents the angle between magnetic flux surfaces and contours of J, the second adiabatic invariant [1]. This was done while also maintaining MHD stability and good neoclassical confinement. In addition, the alpha particle losses have been simulated and compared between the original and optimized equilibria in order to measure the effectiveness of this optimization strategy, which has not before been used for a QA stellarator. The starting equilibrium was the LI383 equilibrium, a 3-period QA stellarator, scaled to the magnetic field strength of the proposed permanent magnet stellarator PM4STELL [2].

1. A. Bader et al 2019 J. Plasma Phys. 85 905850508

2. D. Gates et al 2019, 61^st Annual Meeting of the APS Division of Plasma Physics, BP10.00047