Power Exhaust and Particle Balance Studies on ST40*

ST40 is a private funded, compact, high magnetic field (B_tor > 2T) spherical tokamak (ST) designed, built, and operated by Tokamak Energy Ltd in the United Kingdom [1]. ST40 can operate up to 0.7 MA of plasma current, I_p, ≤ 1.8 MW of neutral beam power, in high-field side (HFS) limited discharges and is developing plasma scenarios for diverted upper single null (USN) and disconnected double null (DN) discharges.  ST40 has achieved record plasma ion temperatures of more than 100000000 K [2] in the HFS limited configuration.  Initial power loading on the graphite, limiter plasma facing components (PFCs) shows peak heat fluxes > 9 MW/m² during the I_p flat-top in qualitative agreement with predictions of peak heat flux and limiter wetted area from the HEAT code [3].  Additionally, a 0-D particle balance of these HFS limited discharges will be shown. Initial results from development of diverted discharges will be presented as well as experimental plans for the next campaign.

[1] M. Gryaznevich, O Asunta and the Tokamak Energy Ltd Team, “Overview and status of construction of ST40,” Fus. Eng. Design. 123 (Nov 2017) 177-180 

[2] S.A.M. McNamara et. al., “Achievement of ion temperatures in excess of 100 million degrees Kelvin in the compact high-field spherical tokamak ST40.” Nucl. Fusion. 63(5) (2023) 054002

[3] T. Looby et. al., “A Software Package for Plasma-Facing Component Analysis and Design: The Heat Flux Engineering Analysis Toolkit (HEAT),” Fus. Sci. Tech. 78 (2022) 10 – 27