Confinement of nonneutral plasmas in a trap composed of a cusped magnetic field and an electrostatic octapole field

The field configuration formed by the superposition of a cusped magnetic fi eld and an electrostatic octapole field provides a closed system of confine ment for a charged particle. In a cusped magnetic field, the Stormer region which constrains a charged particle is open, but it is closed by adding a potential barrier made by the octapole field. One-component plasmas are thu s expected to be confined in this configuration: preserving superior charac teristics of the cusp field for plasma stability. A preliminary experiment was performed on the confinement of electrons in this field configuration. An electron plasma was confined for 3 s in a magnetic field as weak as B = 50 G at the circular line cusp. The confinement time was roughly proportion al to B-2, suggesting that the confinement would be improved substantially in a higher magnetic field.