Piecewise omnigenous stellarators with zero bootstrap current

TL;DR

This paper proves analytically and confirms numerically the existence of piecewise omnigenous stellarator configurations that achieve zero bootstrap current, expanding options for stellarator reactor design with low neoclassical transport.

Contribution

It introduces and demonstrates the existence of piecewise omnigenous fields with zero bootstrap current, broadening stellarator design possibilities.

Findings

Analytical proof of zero bootstrap current in piecewise omnigenous fields

Numerical confirmation of the existence of such fields

Establishment of piecewise omnigenity as a viable stellarator design approach

Abstract

Until now, quasi-isodynamic magnetic fields have been the only known stellarator configurations that, at low collisionality, give small radial neoclassical transport and zero bootstrap current for arbitrary plasma profiles, the latter facilitating control of the magnetic configuration. The recently introduced notion of piecewise omnigenous fields has enormously broadened the space of stellarator configurations with small radial neoclassical transport. In this Letter, the existence of piecewise omnigenous fields that give zero bootstrap current is proven analytically and confirmed numerically. These results establish piecewise omnigenity as an alternative approach to stellarator reactor design.