  Confinement of single ions in a novel radio-frequency (RF) quadrupole ion
trap with spherical shape is investigated. An optimization of this spherical
ion trap (SIT) is carried out in order to suppress its nonlinearity
substantially by eliminating the electric octupole moment. Hence, a trapping
potential and consequently an electric field very similar to the ideal
quadrupole ion trap (QIT) are obtained. Afterwards, three stability regions for
the optimized SIT are numerically computed. The regions coincide well with
those reported in the literature for the ideal QIT. The reason is attributed to
the zero electric octupole moment of our proposed trap. The SIT simple geometry
and relative ease of fabrication along with its increased trapping volume
compared to the conventional hyperbolic quadrupole ion trap, make it an
appropriate choice for miniaturization.
