EXTENSIONS OF THE TOKAMAK—SPHERICAL TORUS AND SPHEROMAK
FIGURE F.2 Examples of the magnetic topologies of three related toroidal configurations with increasing curvature and varying stability characteristics. The tokamak (left) uses a strong external toroidal field to provide robust stability against pressure- and current-driven instabilities. The spherical torus (center) uses a weak toroidal field in a compact configuration to allow access to higher β values than those obtained in the tokamak. The spheromak (right) uses internal plasma currents only to provide the confining poloidal field plus a weak toroidal field. A larger safety factor indicates a higher level of protection from current-driven instabilities. Courtesy of M. Peng, Princeton Plasma Physics Laboratory.