Piecewise omnigenous magnetohydrodynamic equilibria as fusion reactor candidates

TL;DR

This paper introduces a novel stellarator magnetic configuration that achieves high levels of piecewise omnigenity, leading to improved confinement, stability, and transport properties, making it a promising candidate for fusion reactors.

Contribution

It presents a new MHD equilibrium configuration that satisfies ideal conditions and exhibits unprecedented piecewise omnigenity, expanding viable stellarator designs.

Findings

Reduced radial transport and fast ion losses

Enhanced MHD stability across various ta values

Compatible rotational transform profile with island divertor

Abstract

In piecewise omnigenous magnetic fields, charged particles remain perfectly confined in the abscence of collisions and turbulence. This concept extends the traditional notion of omnigenity, the theoretical principle upon which most of existing magnetic fusion reactor designs, including tokamaks, are based. While piecewise omnigenity broadens the range of potentially viable stellarator reactor candidates, it is achieved by relaxing the requirement of continuity in the magnetic field strength, which could appear to pose significant challenges for the design of magnetohydrodynamic equilibria. In this work, a stellarator magnetic configuration is presented that satisfies the ideal magnetohydrodynamic equilibrium equation and that achieves unprecedented levels of piecewise omnigenity. As a result, it exhibits favorable transport characteristics, including reduced bulk radial (neoclassical and turbulent transport), bootstrap current and fast ion losses. In addition, the configuration displays robust MHD stability across a range of \b{eta} values and possesses a rotational transform profile compatible with an island divertor. Collectively, these features satisfy the standard set of physics criteria required for a viable reactor candidate which, until now, were believed to be attainable only by certain types of omnigenous stellarators.