Evaluation of the fusion power via beam-target reaction on EAST and CFETR

This study quantifies deuterium-tritium (D-T) fusion power contributions from beam-target reactions in the EAST and CFETR tokamaks, providing support for the planned trace tritium experiments on EAST. A simplified model for tokamak beam-target fusion power is developed, incorporating fast-ion radial distributions. The model is validated against JET's tritium-rich experimental scenario, where beam-target reactions predominate. Simulations assume a tangentially injected neutral beam with a 0.1 m circular cross-section, centered midway between the torus inner wall and magnetic axis. Analysis for individual beam particles shows that the beam-target fusion energy gain Q_bt increases significantly with bulk plasma temperature and logarithmically with density. For multi-particle systems, the total beam-target fusion power is enhanced by both a higher beam absorption rate and a more peaked fast-ion spatial distribution. As bulk plasma density increases, the beam absorption rate rises towards saturation while the fast-ion spatial distribution broadens radially from the core towards the edge. Consequently, an optimum bulk plasma density exists that maximizes the beam-target fusion power. Density scans for EAST reveal a peak beam-target fusion power of 0.45 MW (Q_bt of 0.1) at the bulk plasma ion density n_i0= 4.05×10¹⁹ m⁻³ (total deuterium and tritium with ratio of 50/50). Unlike thermal fusion scaling with the square of the bulk plasma density, this represents a notable enhancement in beam-target fusion power and reduction in tritium consumption compared to the higher bulk plasma density case. Due to high bulk plasma temperature in CFETR, the beam target fusion energy gain is higher than EAST and the thermal fusion dominates in the total fusion. With n_i0=10.2×10¹⁹ m⁻³, CFETR obtains 10.42 MW (Q_bt of 0.35) beam-target fusion power and ~1 GW thermal fusion power.