The Malmberg-Penning Trap

Nonneutral plasmas are often contained in Malmberg-Penning traps. These cylindrically symmetric traps use a uniform axial magnetic field to provide radial confinement and applied end potentials provide axial confinement. The containment apparatus is shown schematically in the figure above. Because the plasma is nonneutral, there is a self-electric field which causes the plasma to ExB rotate.

The trap is contained inside a vacuum chamber, with pressures typically below 10^-8 Torr and the entire apparatus is immersed in a uniform static axial magnetic field.

The source of the electrons (cathode) is from a directly heated spiral of tungsten wire. Electrons are trapped using an inject, hold, and dump cycle.

For a simpler explanation of how the trap works, check out the EDG poster.