Buffer-gas-free mass-selective ion centering in Penning traps by simultaneous dipolar excitation of magnetron motion and quadrupolar excitation for interconversion between magnetron and cyclotron motion

A new excitation scheme of the radial ion-motional modes is introduced for Penning-trap ion-cyclotron-resonance experiments. By simultaneous dipolar excitation of the magnetron motion and resonant quadrupolar excitation for the conversion between magnetron motion and cyclotron motion, a mass-selective recentering of the ions of interest is performed while all other (contaminant) ions are ejected from the trap. This new technique does not rely on the application of a buffer gas as presently used [G. Savard, St. Becker, G. Bollen, H.-J. Kluge, R.B. Moore, Th. Otto, L. Schweikhard, H. Stolzenberg, U. Wiess, Physics Letters A 158 (1991) 247] and will thus prevent charge-exchange reactions and damping of the motion that decreases mass resolving power.

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► We investigate a new excitation scheme for mass-selective ion centering in Penning traps.
► A dipolar excitation at the ions’ magnetron frequency and a quadrupolar excitation at the cyclotron frequency are superimposed.
► We present the theory of the ions’ motion and first experimental tests of the new method.
► The experiment yields high resolving powers for mass selection.