US Patent 7351965 Rotating excitation field in linear ion processing apparatus

Methods for applying an RF field in a two-dimensional electrode structure include applying RF voltages to main electrodes and to compensation electrodes. The voltages on the compensation electrodes may be adjusted to be proportional to the voltages on the main electrodes. The adjustment(s) may be done to optimize the RF field for different modes of operation such as ion ejection and ion dissociation. For dissociation, a supplemental RF dipole may be applied, or two mutually orthogonal dipoles may be applied in phase quadrature to form a circularly polarized field. Electrode structures may include main trapping electrodes, one or more compensation electrodes, one or more ion exit apertures, and means for applying the various desired voltages.