Some Observations on Higher-order Non-linear Resonances in a Paul Trap
✍ Scribed by R. Alheit; Th. Gudjons; S. Kleineidam; G. Werth
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 695 KB
- Volume
- 10
- Category
- Article
- ISSN
- 0951-4198
No coin nor oath required. For personal study only.
✦ Synopsis
We present some detailed measurements on instabilities of ion trajectories in a Paul trap caused by deviations of the ideal quadrupole potential by trap imperfections. Numerous lines of reduced stabfity have been observed. Their podtion in the stability diagram can be well explained by theory. The identification of a non-linear resonance can be performed by a measurement of the ions' macrofrequendes w,, %. We have observed space charge shifts of the resonances. From the strength and shape of a non-linear resonance, one m a y posdbly determine the contribution of a particular perturbation to the quadrupole potential, and thus characterize the specific trap.
The stability of ion trajectories in an ideal radio-frequency quadrupole ion trap (Paul-trap, QUISTOR) depends on the value of dimensionless stability parameters a and q: 4eU0 a,= -hz=m?a2 z and r are the axial and radial coordinates of the rotational symmetric electrode structure, U, and V, the amplitudes of the DC and AC voltages applied to the electrodes, respectively, 0 the frequency of the AC trapping field, m the mass of the stored ion, and r, the radius of the ring electrode. We have assumed that r, and the closest distance between the endcap electrodes 2 ~0 are related as ro/zi,=fiz, as it is often the case. Stability of the ion motion in an ideal quadrupole trap is assured when a and q have values inside the boundary of a stability diagram gives by the solution of the equation of motion in the time-dependent electric potential. The solution is characterized by parameters &, p,, which depend on a,,, and q,,z: