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 approximately 0.6-0.75 m, R₀/a approximately 1.8-2.5, and B_t0 approximately 1.4-2.2 T can be driven with P_tot approximately 4.5 MW to maintain I_p approximately 0.5 MA and produce the ITER-level plasma edge and divertor conditions. Given an adequate steady-state divertor solution and Q approximately 1 operation based on fusion through the suprathermal component, D-T-fueled tokamaks with R₀ approximately 0.8 m, R₀/a approximately 2, and B_t0 approximately 4 T can be driven with P_tot approximately 15 MW to maintain I_p approximately 4.6 MA and produce a peak neutron wall load W_L approximately 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%.