Linear Ion Trap Aperture Design for Field Homogeneity
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Solution Overview
Problem
Two-dimensional ion traps face significant challenges due to axial field inhomogeneities and mechanical errors, which degrade the resolution and mass accuracy of mass spectrometers, primarily caused by the introduction of apertures that disrupt the quadrupole potential and structural integrity of the rods.
Innovation Solution
A linear ion trap design featuring an aperture that extends radially and longitudinally through the rods, with recesses adjacent to the aperture that do not penetrate radially, minimizing axial field inhomogeneities and preserving structural integrity, thereby optimizing the quadrupole potential and reducing fringe effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an aperture is introduced into the rod to allow ion ejection, then ion ejection efficiency is improved, but the quadrupole potential is degraded and structural integrity is compromised
Solution Approach 1:
The aperture is segmented into multiple sections along the rod length, with each section having controlled dimensions. This segmentation allows the aperture to provide sufficient ion ejection pathways while maintaining the overall quadrupole potential integrity by limiting the disruptive effect to localized regions rather than compromising the entire rod structure.
Solution Approach 2:
The aperture design implements local quality by concentrating the ejection function in specific localized regions of the rod rather than uniformly compromising the entire structure. The aperture sections are strategically positioned and dimensioned to provide necessary ion ejection efficiency while preserving the quadrupole potential in critical regions, thus resolving the contradiction between ejection efficiency and potential integrity.
2Manufacturing precision
If the aperture extends along the entire length of the rod, then axial field homogeneity is improved, but structural integrity and manufacturing feasibility deteriorate
Solution Approach 1:
Instead of a continuous aperture extending along the entire rod length, the design uses multiple discrete aperture sections distributed along the rod. This segmentation achieves adequate axial field homogeneity by providing distributed ejection pathways while maintaining manufacturing feasibility, as each discrete section is easier to fabricate and assemble than a continuous long aperture.
Solution Approach 2:
The aperture sections extend along a substantial fraction of the rod length (achieving near-full coverage) but are implemented as discrete partial sections rather than a complete continuous aperture. This partial action approach provides sufficient axial field homogeneity for practical purposes while avoiding the manufacturing complexities and structural weaknesses of a fully continuous aperture.
3Strength
If the aperture is limited to a fraction of the central region, then structural integrity is improved, but axial field inhomogeneity increases
Solution Approach 1:
The aperture is divided into multiple discrete sections distributed along a substantial fraction of the rod length, rather than being confined to a single central region. This segmentation strategy maintains structural integrity by limiting material removal at any single location while reducing axial field inhomogeneity through the distributed arrangement of aperture sections along the rod length.
Solution Approach 2:
The aperture design transitions from a purely radial aperture (single dimension) to a three-dimensional structure with radial, axial, and angular components. By extending aperture sections along the axial dimension and distributing them at different angular positions, the design achieves better axial field homogeneity while maintaining structural integrity through the multi-dimensional distribution of the aperture features.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances axial field homogeneity, reduces the complexity of the electronics system, and improves mass resolution and accuracy, achieving performance comparable to segmented rod architectures while maintaining structural integrity.
Implementation Method 1
ions are introduced into or formed and contained within a trapping volume formed by a plurality of electrode or rod structures by means of substantially quadrupolar electrostatic potentials generated by applying RF voltages, DC voltages or a combination thereof to the rods
Implementation Method 2
a two-dimensional or linear ion trap typically includes two pairs of electrodes or rods, which contain ions by utilizing an RF quadrupole trapping potential in two dimensions
Implementation Method 3
a non-quadrupole DC trapping field is used in the third dimension
Implementation Method 4
When using a mass selective instability scan in a linear ion trap, the ions are most efficiently ejected from the trap in a radial direction
Data Source
Figure 1~2
Figure 3~5
Figure 4A~4D
AI summary
An aperture design for a linear ion trap is provided in which the aperture is optimized to minimize possible axial field inhomogeneities whilst preserving the structural integrity of the quadrupole rods. In general, the invention provides a linear ion trap for trapping and subsequently ejecting ions. The linear ion trap comprises a plurality of rods which define an interior trapping volume which has an axis extending longitudinally. One or more of the rods includes an aperture which extends both radially through the rod and longitudinally along the rod. The aperture being configured such that the ions can pass from the interior trapping volume through the aperture to a region outside the interior trapping volume. At least one recess is disposed adjacent the aperture, extending longitudinally along the rod and facing the interior trapping volume, the recess not extending radially through the rod.