Miniature Paul—Straubel ion trap with well-defined deep potential well

Abstract

In some recently proposed experiments using ion traps, a Paul trap of conventional size and design is insufficient. We have constructed a miniature Paul-Straubel trap. It has a small elliptic ring (-0.2 mm) and three pairs of planar electrodes (-2 cm part) arranged so that they form a cube. The two conventional end-cap electrodes are replaced by the six planar electrodes. The ring is heatable to a high temperature for improving the uniformity of the dc potential on the ring surface. With this trap, we hope to do such fundamental studies as the true zero-point confinement of a single ion. COConventional Paul traps for single ion spectroscopy (1-5) are composed of a ring and two end-cap electrodes. When an rf voltage is applied between the ring and end-caps, it forms a three-dimensional harmonic oscillator pseudopotential. Typical size traps are of 1 mm ring diameter. The small size makes controlling orientation in space of the principal axes of the elliptical confining potential very difficult and no previous design has succeeded in doing so. To increase the trapping strength, an even smaller ring size has to be used. Another serious problem with all of the traps used has been the stray offset dc fields existing in the trap. It is well known that such offset potentials introduce a large unwanted micromotion of the trapped ions (5), preventing one from obtaining ultrahigh-resolution spectra or achieving real zero-point confinement-an ultimate demonstration of the quantum-mechanical analogue of a particle at rest in free space.To remedy these problems, we constructed a miniature trap as shown in Fig. 1. In this trap, a Paul-Straubel trap, the usual two end-cap electrodes are replaced by two parallel metal plates perpendicular to the z axis, being 1 cm away from the ring electrode. Any stray dc potentials on the plates would then have a much smaller effect at the center of the ring. The elliptic ring itself, 0.2 mm in diameter and slightly elongated in the y direction, is made of a thin tungsten wire, with two small leads, which attach to two rigid supporting rods (not shown in Fig. 1). By running a large current through the ring, it is possible to heat the ring to a very high temperature at which any surface layer would be cleaned up to the atomic level. This operation should greatly reduce, if not completely remove, the contact potential on the ring surface and accordingly reduce the stray electric fields present at the center of the pseudopotential well. The clean-up process can of course be repeated even in an operating trap. There are also two pairs of auxiliary plates placed on the four sides of the ring perpendicular to the x and y axes, respectively. They are so arranged that the four side plates and the two end plates are on the surfaces of a cube with the ring at its center. Applying some small voltage between the pairs of opposite plates should make it possible to null out any residual stray dc fields at the center of the trap.Straubel (6) showed trapping of macroscopic charged particles using a ...

Comparison of the activation time effects and the internal energy distributions for the CID, PQD and HCD excitation modes

“…This empirical mass‐dependent equation for the ion trap instruments (reported in Supporting Information) allows the normalization of the collision energy according to the m/z value of the precursor ions. As the internal energy is statistically distributed over each degree of freedom (DOF) (equilibrium process), the internal energy required to achieve ion dissociation depends mainly on the m/z values of the ion and its position in the potential well of linear ion traps . Note that this empirical equation may change depending on the operating parameter maintenance of the instrument.…”

“…First, the activation of the precursor ion occurs at high q (i.e. a typical q value of 0.7 corresponding to a deeper position in the deep potential well of a linear ion trap and consequently to a very stable ion trajectory to avoid its ejection during activation). A short excitation pulse (0.1 ms) increases the kinetic energy of the precursor ion and converts this increase in kinetic energy into internal energy by collisions.…”

Optical atomic clocks

“…A stronger variation of the original Paul design in which the end cap electrodes are pulled away from the ring was introduced by Straubel (1955). It also offers larger optical access and can be implemented in several variations (Yu, Dehmelt, and Nagourney, 1989;Yu, Nagourney, and Dehmelt, 1991;Schrama et al, 1993). An even more open geometry with good approximation of quadrupole potential is obtained with the end cap trap (Schrama et al, 1993), where the ring is replaced by two cylindrical shields that surround the rfcarrying end cap electrodes [see Fig.…”

Trapped ion optical frequency standards

“…While these actual shapes may well give rise to greater anharmonicities, these are not too severe for the ion sitting close to the trap centre. Other designs used for frequency standards also include the end-cap trap (Schrama et al 1993) (where there is no ring, its function being achieved by the use of two outer electrodes arranged concentrically around the end-caps), the inverted 'Paul-Straubel' or ring trap (Yu et al 1989) (which is the ring equivalent of the end-cap trap) and the linear ion trap (Prestage et al 1989) where ions are confined in a linear string along the z-axis by means of ac voltages across four electrodes parallel to the axis and a dc voltage applied at each end.…”