Theoretical investigation of unstable axial mass-selective extraction of ions from a nonlinear trap

The unstable axial mass-selective extraction of ions from a three-dimension al quadrupole ion trap is studied theoretically. A method for mapping the i on coordinates over the period of the RF power-supply voltage is developed with allowance for nonlinear distortions of the quadrupole potential. Equat ions for the envelope of ion oscillations are derived in the form of the eq uation of motion of a material point in the field of effective forces. The effect of the "delayed extraction" of ions in the presence of negative even field harmonics is explained. The positive even harmonics of the distorted quadrupole potential are shown to be favorable for ion extraction. The dyn amics of the extracted ions is investigated. (C) 2000 MAIK "Nauka / Interpe riodica".