Patent ID: 7847240

Claim:
An ion extraction method comprising: confining ions within an ion trap extending along a longitudinal axis; exciting a subset of the ions to cause them to oscillate along at least one transverse coordinate; after the transverse excitation, applying a first field in the region of the transverse excitation to move the excited ions towards one end of the ion trap, wherein the first field is configured to produce an axial force that varies with the amplitude of the transverse oscillation of the excited ions and produces substantially no axial force for unexcited ions located along the longitudinal axis; and providing a second field different from the first field to extract at least some of the excited ions through a potential barrier at the end of the ion trap, wherein the second field is configured to provide an axial force whose magnitude varies with the transverse excitation energy of the excited ions and produces substantially no axial force for unexcited ions located along the longitudinal axis.