Spherical torus: an approach to compact fusion at low field. Initial ignition assessments

Initial assessments of ignition devices based on the spherical torus concept suggest that an ignition spherical torus (IST) can be highly cost-effective and exceptionally small in unit size. Assuming advanced methods of current drive and confinement and beta scalings with plasma current, a D-T IST with a toroidal field of 2 to 3 T is estimated to have a major radius ranging from 1 m to 1.6 m, and a fusion power less than 60 MW. For the nominal IST (at 2 T and 1.6 m), the direct cost of the nuclear island is estimated to be about $120 M with a total direct cost about $340 M in mid-1984 dollars based on the Fusion Engineering Design Center (FEDC) cost algorithm. For ISTs with higher field and smaller size (e.g., at 3 T and 1 m), further reductions of the cost of the nuclear island are estimated. In case of confinement scaling with the plasma size only, strong plasma paramagnetism (self-generated magnetic field) in the spherical torus may still serve to compensate for the projected confinement shortfall