Suitability of linear quadrupole ion traps for large Coulomb crystals

TL;DR

This paper evaluates different linear quadrupole ion trap designs for growing large Coulomb crystals, focusing on micromotion, anharmonicity, and resonance heating to identify optimal configurations.

Contribution

It introduces a comparative analysis of trap designs based on micromotion, anharmonicity, and resonance effects, highlighting the advantages of a rotated-endcap trap.

Findings

Rotated-endcap trap shows reduced micromotion and anharmonicity effects.

Significant differences found between trap designs in key parameters.

The analysis aids in optimizing trap design for large Coulomb crystal experiments.

Abstract

Growing and studying large Coulomb crystals, composed of tens to hundreds of thousands of ions, in linear quadrupole ion traps presents new challenges for trap implementation. We consider several trap designs, first comparing the total driven micromotion amplitude as a function of location within the trapping volume; total micromotion is an important point of comparison since it can limit crystal size by transfer of radiofrequency drive energy into thermal energy. We also compare the axial component of micromotion, which leads to first-order Doppler shifts along the preferred spectroscopy axis in precision measurements on large Coulomb crystals. Finally, we compare trapping potential anharmonicity, which can induce nonlinear resonance heating by shifting normal mode frequencies onto resonance as a crystal grows. We apply a non-deforming crystal approximation for simple calculation of these anharmonicity-induced shifts, allowing a straightforward estimation of when crystal growth can lead to excitation of different nonlinear heating resonances. In the axial micromotion and anharmonicity points of comparison, we find significant differences between the compared trap designs, with an original rotated-endcap trap performing slightly better than the conventional in-line endcap trap.