Injection and Storage of Singly Charged Ions and Extension of the Principles of Ion Storage to Highly Charged Low Energy Recoil Ions

Abstract

On-line experiments on low energy multiply charged ions can be performed with high sensitivity and resolution if the ions of interest are caught in flight and are subsequently accumulated in a finite observation volume. The various aspects of injecting singly and multiply charged ions into harmonic and nonharmonic ion trap devices are discussed. Injection of a continuous ion beam into an active trap was evaluated by numerical integration of the Mathieu equations to determine the finite confinement time of the injected ions. Three different modes of operation of the ion trap, namely, the radio-frequency (RF), the Penning, and the combined RF and Penning modes were considered. On the other hand the phase space method was used for a pulsed ion beam injected into the RF quadrupole ion trap for which the RF quadrupole field was switched on after the ion injection. In this way, a high trapping efficiency is reached for a suitable combination of the chosen initial RF voltage phase angle and the delay time after the ion injection. In addition, the trapped ions are confined indefinitely and energy- and mass-selective storage of the injected ions are also possible. The occurrence of ion motion induced side bands in the spectrum of stored ions and their importance for determining the ion temperature are discussed. Scaling relations are given which relate the results obtained for singly charged ions to the storage properties as they pertain to highly charged ions. Use is made of the unique environment of ion traps to speculate about novel collision and high resolution spectroscopy experiments on highly charged ions.