Chaotic motion of single ions in a toroidal ion trap mass analyzer

Abstract

Although widely used in mass spectrometry, radiofrequency ion traps involve complex electric field shape and correspondingly complex ion motion. In addition, numerous variations of electrode geometry have been developed to address or benefit from different aspects of ion motion and the resulting effects on performance as a mass analyzer. We report on SIMION simulations that show classical chaotic behavior of ions in the toroidal ion trap. The chaotic motion is a result of the non-linear components of the electric fields as established by the trap electrodes, and not by Coulombic interaction from other ions. The chaotic behavior was observed specifically in the ejection direction of ions located in non-linear resonance bands within and adjacent to the region of stable trapping. The non-linear bands crossing through the stability regions correspond to hexapole resonance conditions, while the chaotic ejection observed at the boundary of the stable trapping region represents a “fuzzy” ejection boundary. Fractal-like patterns were obtained in a series of zoomed-in regions of the stability diagram.