Particle Dynamics in Damped Nonlinear Quadrupole Ion Traps

TL;DR

This paper investigates particle motion in damped nonlinear quadrupole ion traps, revealing complex stable trajectories and a novel collective behavior where particles form self-stabilized knots of diamond orbits.

Contribution

It introduces a comprehensive analysis of nonlinear effects on particle trajectories and reports the discovery of a new collective behavior in 2D microparticle traps.

Findings

Particles exhibit stable closed orbits influenced by nonlinear damping.

Extended orbits are confined to the trap axis in 3D traps.

Particles spontaneously form self-stabilized knots of diamond orbits.

Abstract

We examine the motions of particles in quadrupole ion traps as a function of damping and trapping forces, including cases where nonlinear damping or nonlinearities in the electric field geometry play significant roles. In the absence of nonlinearities, particles are either damped to the trap center or ejected, while their addition brings about a rich spectrum of stable closed particle trajectories. In three-dimensional (3D) quadrupole traps, the extended orbits are typically confined to the trap axis, and for this case we present a 1D analysis of the relevant equation of motion. We follow this with an analysis of 2D quadrupole traps that frequently show diamond-shaped closed orbits. For both the 1D and 2D cases we present experimental observations of the calculated trajectories in microparticle ion traps. We also report the discovery of a new collective behavior in damped 2D microparticle ion traps, where particles spontaneously assemble into a remarkable knot of overlapping, corotating diamond orbits, self-stabilized by air currents arising from the particle motion.