CONFINEMENT OF IONS INJECTED INTO A RADIOFREQUENCY QUADRUPOLE ION TRAP - PULSED ION-BEAMS OF DIFFERENT ENERGIES
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abstract
The ion confinement properties of a radiofrequency (r.f.) quadrupole ion trap with phase-synchronized switching-on of the driving r.f. field are evaluated for ion pulses injected from an external source. Singly charged ions of mass 100 u are considered. Calculations are performed for well-collimated pulsed ion beams, with a finite circular cross-section 1 mm in diameter, injected into an r.f. quadrupole trap with characteristic dimension ro = 5.4 mm. Ion injections along the gap and through an aperture in one of the electrodes, including. typical off-axial- and off-equatorial-plane incidence directions, are considered. The ion confinement property of the r.f. quadrupole trap for externally injected ions is energy-dependent. The optimum time delays before turning on the quadrupole field have different values for injected ions of different energies. For an injected ion beans with a large energy-spread the overall ion-trapping efficiency therefore cannot reach unity. The phase-dependence of the overall ion-trapping efficiency is shown for an ion beam of uniform energy distribution over the range 0-20 eV. By suitably choosing the experimental conditions, energy-selective storage of the injected ions should be possible. 1981.