Steady-state and ELM heat flux load predictions on ST40 limiter and divertor PFCs*

ST40 is a high field (B_tor > 2T) spherical tokamak operated by Tokamak Energy Ltd with an aspect ratio of 1.6 -1.8. ST40 can operate up to 0.7 MA of plasma current, I_p, with up to 1.8 MW of auxiliary heating, P_aux, in various magnetic geometries for ~0.5 sec pulse durations. One of the biggest challenges in high-performance tokamak operations is the management of heat flux on plasma-facing components (PFCs) such as divertors, as these materials are designed to dissipate the plasma heat and particle loads. This makes the PFCs very susceptible to damage and failure. In this research, the Heat Flux Engineering Analysis Toolkit (HEAT) [1] is used to predict the effects of P_aux, I_p, and magnetic geometry on the heat loads to the divertors and limiters of the ST40 tokamak. MHD equilibrium for diverted (single and double null) and limited plasmas were generated using the FIESTA code. Initial steady-state simulations used P_aux of 1.8 MW for a double null plasma and a prescribed Eich radial heat flux profile. This simulation showed that large heat loads (>20 MW/m²) were deposited on the divertors. Initial attempts to predict ELM heat loads on the PFCs will also be shown. The results from these simulations are essential in designing future experiments that fully-protect the PFCs as well as validating heat flux predictions for future devices.

[1] T. Looby et. al., A Software Package for Plasma-Facing Component Analysis and Design: The Heat Flux Engineering Analysis Toolkit (HEAT), Fusion Science and Technology 78 (2022), 10 – 27.