Overview of ST40 high-field spherical tokamak and recent results

ST40 [1] is a high-field spherical tokamak (ST) built and operated by Tokamak Energy Ltd. It is a step on the Company’s roadmap to develop commercial fusion power plants based on the ST concept and utilizing magnets made of high temperature superconductors. ST40 is equipped with copper magnets and heated using two co-current neutral beam injectors that deliver up to 1.0MW of 55keV, and 0.8MW of 24keV neutrals. Thus far, ST40 has been operated at Bt≤2.2T, Ip=350–800kA R₀=0.4–0.5m, and A=1.6–1.8. After reaching the 100MK ion temperature milestone in 2022 [1], ST40 went through a series of hardware upgrades to improve its diagnostic capabilities and in preparation for diverted operations. These included new coil power supplies and new diagnostic systems such as: Thomson Scattering (TS), tangential midplane bolometer and soft X-ray (SXR) cameras, divertor infra-red (IR) camera, and Langmuir probes. The first operations with these improvements aimed at commissioning the new diagnostics and developing double-null diverted (DND), upper single-null diverted (USND), and high-β_p scenarios. The results of these experiments and plans for future experimental Campaigns will be presented.

[1] S.A.M. McNamara, et al., Nucl. Fusion 63 (2023) 054002

[2] M. Gryaznevich, O. Asunta, Fusion Eng. Des. 123 (2017) 177-180