Higher order theory of quasi-isodynamicity near the magnetic axis of stellarators

Abstract

The condition of quasi-isodynamicity is derived to second order in the distance from the magnetic axis. We do so using a formulation of omnigenity that explicitly requires the balance between the radial particle drifts at opposite bounce points of a magnetic well. This is a physically intuitive alternative to the integrated condition involving distances between bounce points, used in previous works. We investigate the appearance of topological defects in the magnetic field strength (``puddles''). A hallmark of quasi-isodynamic fields, the curved contour of minimum field strength, is found to be inextricably linked to these defects. Our results pave the way to constructing solutions that satisfy omnigenity to a higher degree of precision, and also to simultaneously consider other physical properties, like shaping and stability.

References in corpus (9)

• Constructing stellarators with quasisymmetry to high order
• Necessary and Sufficient Conditions for Quasisymmetry
• Mapping the space of quasisymmetric stellarators using optimized near-axis expansion
• Direct construction of optimized stellarator shapes. III. Omnigenity near the magnetic axis
• Near-Axis Expansion of Stellarator Equilibrium at Arbitrary Order in the Distance to the Axis
• A single-field-period quasi-isodynamic stellarator
• Solving the problem of overdetermination of quasisymmetric equilbrium solutions by near-axis expansions: I. Generalised force balance
• Phases and phase-transitions in quasisymmetric configuration space
• Higher order theory of quasi-isodynamicity near the magnetic axis of stellarators

Cited by in corpus (5)

• Constructing the space of quasisymmetric stellarators
• Higher order theory of quasi-isodynamicity near the magnetic axis of stellarators
• The zonal-flow residual does not tend to zero in the limit of small mirror ratio
• Electron root optimisation for stellarator reactor designs
• Near-axis quasi-isodynamic database