Curved Ion Trap Electrodes for Space Charge and Focusing
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Solution Overview
Problem
Existing ion traps face limitations in space charge capacity, focusing capabilities, and manufacturing complexity, particularly when dealing with high space charge requirements and the need for precise ion beam focusing for mass analyzers like orbitraps and multi-reflection time-of-flight analyzers.
Innovation Solution
An ion trap design featuring elongate trapping electrodes with varying curvatures and sectional areas along its axis, creating a non-linear trapping field that allows for enhanced ion storage and ejection capabilities, including a quasi-potential well with a non-constant coefficient of parabolicity, enabling better ion focusing and increased space charge capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a 3D quadrupole ion trap is used for ion accumulation, then ion storage capability is provided, but the limited volume of the ion cloud results in significant Coulomb interactions that greatly affect parameters of resulting ion beams
Solution Approach 1:
The patent transitions from a compact 3D quadrupole trap to a linear ion trap configuration, effectively adding a spatial dimension along the trap axis. This elongated geometry distributes ions over a larger volume, reducing ion density and consequently minimizing Coulomb interactions while maintaining ion storage capacity.
Solution Approach 2:
The patent employs curved ion trap configurations including circular, helical, and banana-shaped geometries. These curved paths increase the effective trapping volume and allow ions to be distributed along curved trajectories, thereby reducing ion density and Coulomb interactions compared to straight linear configurations.
2Quantity of substance
If linear ion traps and curved ion traps are used to increase ion cloud volume, then space charge effects are reduced, but subsequent focusing in the axial direction becomes problematic
Solution Approach 1:
The patent applies different curvature characteristics to different sections of the ion trap. For example, the central region may have one curvature radius while the end regions have different curvature radii, allowing optimization of both ion distribution (reducing space charge) and focusing capability at specific locations along the trap axis.
Solution Approach 2:
The patent employs variable RF voltages applied to different segments of the trap electrodes, allowing dynamic control of the electric field distribution. This enables adjustment of the trapping potential landscape to achieve both adequate ion distribution and proper focusing at the trap exit.
3Manufacturing precision
If curved focusing and deflection optics are used between the trap and orbitrap mass analyser, then ion focusing is improved, but the construction becomes complicated and requires wide slits leading to increased requirements on differential pumping
Solution Approach 1:
The patent designs the ion trap electrodes to serve multiple functions: they provide ion confinement through RF fields, create focusing fields through their curved geometry, and define the ejection trajectory. This multi-functionality eliminates the need for separate curved focusing optics, simplifying the overall construction while maintaining focusing capability.
Solution Approach 2:
The patent extracts the focusing function from separate optical components and integrates it directly into the ion trap electrode structure itself. The curved trap electrodes generate the necessary focusing fields as an inherent property of their geometry, removing the need for additional curved focusing and deflection optics.
4Quantity of substance
If curved ion trap with orthogonal ejection is used, then high space charge capacity is achieved, but the trap suffers from lower space charge capacity than the orbitrap itself and requires complex curved lenses
Solution Approach 1:
The patent transitions from orthogonal ejection (perpendicular to the trap axis) to axial ejection (parallel to the trap axis). This dimensional change in ejection direction allows for simpler lens systems while maintaining high space charge capacity, as the ion beam naturally follows the trap axis and requires less complex steering and focusing.
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 allows for a wider mass range of ions to be trapped and ejected, improved focusing, reduced manufacturing costs, and increased space charge capacity, while enabling ions to be ejected independently of mass-to-charge ratio, with narrower slits for differential pumping and sharper focusing.
Implementation Method 1
a power supply for supplying an rf voltage to the trapping electrodes, characterised in that the shape of the trapping electrodes and/or the magnitude of the applied rf voltage are chosen so as to create an electric field within the trapping volume
Implementation Method 2
create an electric field within the trapping volume which imposes an electric force on ions therein
Data Source
AI summary
An ion trap comprises substantially elongate electrodes 10, 20 some of which are curved along their axis of elongation and which define a trapping volume between them. The sectional area of this trapping volume towards the extremities of the trap in the direction of elongation is different to the sectional area away from its extremities (eg towards the middle of the trap). In a preferred embodiment, the trap has a plurality of elongate electrodes, wherein opposed electrodes have different radii of curvature so that the trap splays towards its extremities. Thereby, a wider mass range of ions can be trapped and ejected, a higher space charge capacity (for a given trap length) is provided, and sharper ion beam focussing on ejection is possible.