STAR_Lite: A stellarator designed to experimentally validate non-resonant divertors

TL;DR

STAR_Lite is a new stellarator experiment designed to validate non-resonant divertors, demonstrating their robustness across various configurations and resilience to magnetic perturbations, with implications for plasma exhaust management.

Contribution

The paper introduces the design and analysis of STAR_Lite-A, a flexible stellarator configuration that experimentally validates the robustness of non-resonant divertors in a quasi-axisymmetric setup.

Findings

NRDs persist across different configurations

Heat exhaust remains resilient to coil current variations

X-points and quasisymmetry are preserved under magnetic perturbations

Abstract

The non-resonant divertor (NRD) offers a promising exhaust solution for stellarators, combining topological simplicity with resilience to magnetic field perturbations. To experimentally validate the robustness of non-resonant divertors in a quasi-axisymmetric (QA) configuration, we introduce STAR_Lite, a new stellarator experiment at Hampton University. This paper details the design and analysis of the first STAR_Lite coil configuration, STAR_Lite-A. The two field-period configuration manifests an NRD through X-points with zero rotational transform, at the top and bottom of the device. The divertor legs extruding from the X-points are topologically similar to the poloidal divertors of tokamaks. To expand the experimental range, STAR_Lite-A is optimized for experimental flexibility, producing a wide range of distinct QA configurations by only varying the currents in the modular coils. The NRDs not only persist across these configurations, but numerical strike-line simulations confirm that heat exhaust remains resilient to changes in coil currents, with plasma following the divertor legs and creating a toroidal, discontinuous, strike pattern. We further examine the resilience of the NRD to magnetic perturbations caused by manufacturing errors in the modular coils. We find that quasisymmetry and the existence of X-points is well-preserved under these magnetic field changes, but the rotational transform may vary substantially and displacements of the divertor X-points may lead to one X-point having a dominant effect on edge transport. Overall, our analysis indicates a compact, modular design can likely generate a resilient NRD structure while satisfying the practical constraints of a university-scale experiment.