Results of a preliminary conceptual design of a magnetic fusion reactor based on the spherical torus (tokamak), characterized by high first-stability-regime beta values at low aspect ratio and moderate vertical elongation of the plasma, are described. The concept incorporates resistive (demountable) toroidal-field coils, a double-null poloidal-field magnetic divertor, and the potential for oscillating-field current drive to allow steady-state operation. The physics basis, design-point determination, and fusion-power-core engineering are summarized.