Toroidal Plasma Traps

Abstract

A magnetic field keeps the plasma from drifting to the side walls, but has no effect on motion toward the ends of a tube. A simple way of producing a magnetic trap is to make an endless tube. We simply bend the tube into a circle, as shown in Fig. 9. A body similar to a doughnut or bagel has a special geometric name, the torus. A magnetic trap of this form is referred to as toroidal. An external coil or solenoid generates a magnetic field along the tube. This field keeps the plasma from drifting in the transverse direction into the walls. Although the plasma moves freely along the field this motion does not result in plasma loss. The magnetic field lines are closed into circles and do not intersect the walls of the bottle. However, plasma confinement in a toroidal trap is complicated by the fact that the magnetic field cannot be homogeneous in such a trap.