Rotating-radio-frequency ion traps.

We discuss a new ion trap, the rotating-radio-frequency (rotating-rf) trap, in which the motion of a charged particle is described by trigonometric functions rather than the usual Mathieu functions of a normal rf trap.\footnote{R.I. Thompson, et al., Can. J. Phys. {\bf 80}, 1433 (2002).}$^,$\footnote{T. Hasegawa et al., Phys. Rev. A {\bf 72}, 043403 (2005).} In the rotating-rf trap, a rotating quadrupole electric field confines charged particles, whereas in a normal rf trap, an oscillating quadrupole electric field does. Ion motion in a rotating-rf trap is a superposition of two non-degenerate circular secular motions and two corresponding circular micromotions. The cases of applying a uniform dc magnetic field and a quadrupole dc electric field in addition to the rotating rf field are also discussed. Confinement in a rotating-rf trap can be tighter than in a normal linear rf trap with the same experimental parameter values.