Small Tokamaks for Fusion Technology Testing

Small steady-state tokamaks for testing divertors and fusion nuclear technologies are considered. Based on present physics and technology data and extrapolation to reduced R₀/a, H-D-fueled tokamaks with R₀ ∼ 0.6–0.75 m, R₀/a ∼ 1.8–2.5, and B_t0 ∼ 1.4–2.2 T can be driven with P_tot ∼ 4.5 MW to maintain I_p ∼ 0.5 MA and produce the ITER-level plasma edge and divertor conditions. Given an adequate steady-state divertor solution and Q∼1 operation based on fusion through the suprathermal component, D-T-fueled tokamaks with R₀ ∼ 0.8 m, R₀/a ∼ 2, and B_t0 ∼ 4 T can be driven with P_tot ∼ 15 MW to maintain I_p ∼ 4.6 MA and produce a peak neutron wall load W_L ∼ 1 MW/m². Such devices appear possible if the plasma properties at the lower R₀/a remain tokamak-like and, for the D-T case, an unshielded center core is feasible. The use of a single conductor as the inboard leg of the toroidal field coils for this purpose is discussed. The physics issues and the design features are identified for such tokamaks with a testing duty factor goal of 10–20%.