Axial and radial space-charge effects in radiofrequency gas-filled low-pressure quadrupole ion guides

• Published in: International journal of mass spectrometry Vol. 491; p. 117097
• Main Authors: Yavor, Mikhail I., Shcherbakov, Anatoly P., Pomozov, Timofey V., Kirillov, Sergey N., Vorobjev, Alexey N., Makarov, Vasily V., Verenchikov, Anatoly N.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2023
• Subjects: Gas-filled interface; Mass spectrometer; Radiofrequency quadrupole guide; Space charge; Time-of-flight; Space charge; Radiofrequency quadrupole guide; Mass spectrometer; Gas-filled interface; Time-of-flight
• ISSN: 1387-3806; 1873-2798
• DOI: 10.1016/j.ijms.2023.117097

This paper presents theoretical and experimental study results of the space-charge (SC) effects in gas-filled radiofrequency ion guides, typically operating at ∼1 Pa gas pressures. A self-consistent Coulomb interaction simulation allows modeling the ion self-propulsion by the own SC, optionally supplemented by an external axial field. The simulations are accelerated with an improved collision model, combining the hard-sphere and polarization interaction models. Simulated ion beam parameters are consistent with the experimental measurements performed with an orthogonal accelerating time-of-flight mass spectrometer. The experimental and theoretical studies consistently demonstrate notable SC effects in ion guides, even at moderate ion currents in the sub-nA range. The effects become softer when using a weak ∼0.02 V/mm axial field. The efficiency of the ion guides improves with their miniaturization. The simulations and experiments demonstrate stronger beam compression for multiple-charged ions, even in the presence of SC effects, thus providing shorter turnaround times in orthogonal accelerators. The SC effects depend on the ion beam composition in the ion guides; the presence of light or multicharged ions strongly affects the ion motion of heavier species with a lower charge. [Display omitted] •Self-consistent ion density and velocity distributions in gas-filled quadrupole guides presented.•Optimal ion transport requires applying ∼0.02 V/mm auxiliary axial field.•Efficiency of ion guides is improved with their minituarization•Mass discrimination of heavy low charge ions is expected at nA ion currents.•Simulated space charge effects are consistent with experimental measurements.