Combination of quasi-isodynamic and piecewise omnigenous magnetic fields

This is the authors' abstract. We don't add key points for this paper.

Due to their simultaneous optimization for radial and parallel neoclassical transport, quasi-isodynamic (QI) fields have been the main choice of stellarator magnetic configuration for most fusion reactor candidates in recent years. However, achieving a high degree of quasi-isodynamicity often comes at the cost of a strong shaping of the flux surfaces of the stellarator and complex coil geometries. In this work, the concepts of quasi-isodynamicity and piecewise omnigenity (pwO) are combined to form QI-pwO fields. These fields are QI in the low-field region of the magnetic surface, whereas they significantly depart from quasi-isodynamicity in the high-field region without sacrificing the neoclassical transport properties of QI fields. This departure could make it easier to integrate the optimization of neoclassical transport with other physical and technological aspects of a stellarator reactor.