Plasma confinement in a spindle cusp magnetic field

An experimental study of the confinement properties of a low (average) beta plasma in a spindle cusp magnetic field is described. An argon discharge plasma and a plasma produced by contact ionization of potassium were investigated. Electron and ion densities, space potentials, and plasma flow velocities were measured in the ring and point cusps. The leak width of the escaping plasma was measured over a wide range of magnetic field strengths and neutral gas pressures. The dependence of the leak width on neutral pressure and magnetic field strength is accounted for by a simple model is which plasma streams out of the cusps along the magnetic field lines while diffusing across the magnetic field due to the combined effects of neutral particle collisions and Bohm diffusion