For ion-mode plasma containment, a toroidal vacuum vessel (322) has a major radius (208) and a minor radius (212). The toroidal vacuum vessel (322) is filled with a gas (391) having an initial particle density. An ionizing device (341) ionizes the gas (391) into a plasma (400). A transformer inductively (326) drives a toroidal particle current (332) comprising an ion current and an electron current about a toroidal axis. The toroidal particle current (322) heats the plasma (400) and generates a poloidal magnetic field (373). Field coils (414) wound poloidally about the toroidal vacuum vessel (322) generate a toroidal magnetic field (371). The toroidal magnetic field (371) at a wall of the toroidal vacuum vessel (322) is adjusted to satisfy a boundary condition for a minimum-energy. The plasma (400) is contained by the radial electric field, the poloidal magnetic field (373), and the toroidal magnetic field (371) within the toroidal vacuum vessel (322) in the minimum-energy state.