Minimum magnetic curvature for resilient divertors using Compact Toroidal Hybrid geometry

Abstract

The properties of resilient divertors are explored using equilibria derived from Compact Toroidal Hybrid (CTH) geometries. Resilience is defined here as the robustness of the strike point patterns as the plasma geometry and/or plasma profiles are changed. The addition of plasma current in the CTH configurations significantly alters the shape of the last closed flux surface and the rotational transform profile, however, it does not alter the strike point pattern on the target plates, and hence has resilient divertor features. The limits of when a configuration transforms to a resilient configuration is then explored. New CTH-like configurations are generated that vary from a perfectly circular cross section to configurations with increasing amounts of toroidal shaping. It is found that even small amounts of toroidal shaping lead to strike point localization that is similar to the standard CTH configuration. These results show that only a small degree of three-dimensional shaping is necessary to produce a resilient divertor, implying that any highly shaped optimized stellarator will possess the resilient divertor property.

Advancing the physics basis for quasi-helically symmetric stellarators

“…Divertor Divertors for quasi-symmetric stellarators require either resilience to changes in the plasma current and pressure profiles or active control mechanisms to ensure proper function of a resonant divertor, often referred to as an island divertor, from startup to the operational point (König et al 2002). Properties for non-resonant divertors have been explored both theoretically and numerically (Bader et al 2017(Bader et al , 2018Boozer & Punjabi 2018). In this section we present a methodology for constructing such a divertor, and provide a first attempt at what a non-resonant divertor could look like for a QHS stellarator.…”

“…Properties for non-resonant divertors have been explored both theoretically and numerically (Bader et al. 2017, 2018; Boozer & Punjabi 2018). In this section we present a methodology for constructing such a divertor, and provide a first attempt at what a non-resonant divertor could look like for a QHS stellarator.…”

“…These advances come in several forms including the identification of new quasi-axisymmetric configurations (Henneberg et al 2019b). Advances in theoretical understanding have produced mechanisms for optimization in the areas of turbulent transport (Mynick, Pomphrey & Xanthopoulos 2010;Xanthopoulos et al 2014;, energetic particle transport (Bader et al 2019;Henneberg, Drevlak & Helander 2019a) and non-resonant divertors (Bader et al 2018). Also, construction of optimized equilibria from first principles has been demonstrated for quasi-symmetric stellarators (Landreman & Sengupta 2018;Landreman, Sengupta & Plunk 2019) and quasi-omnigenous stellarators .…”

“…2019; Henneberg, Drevlak & Helander 2019 a ) and non-resonant divertors (Bader et al. 2018). Also, construction of optimized equilibria from first principles has been demonstrated for quasi-symmetric stellarators (Landreman & Sengupta 2018; Landreman, Sengupta & Plunk 2019) and quasi-omnigenous stellarators (Plunk, Landreman & Helander 2019).…”

Stellarators as a fast path to fusion

“…Non-resonant divertors have been explored less than resonant divertors, but there are several theoretical papers on non-resonant divertors [12,[34][35][36]. Unlike resonant divertors, non-resonant divertors place no constraint on the edge rotational transform and the width of the escaping flux tube that carries plasma to the pumps can be adjusted.…”