Ion Guides with RF Diaphragm Stacks for Beam Shaping
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Solution Overview
Problem
Conventional ion guides with stacked diaphragms face challenges in actively driving ions forward and shaping the ion beam, particularly due to the limitations of circular apertures which result in uneven ion distribution and specific mass-dependent ion reflection, leading to inefficient ion extraction and limited mass range.
Innovation Solution
The use of diaphragm stacks with non-circular apertures, such as oval, rectangular, or indented holes, which allow for active forward drive and precise shaping of the ion beam, enabling ion collection along the axis and improved mass selectivity through tailored aperture shapes and voltage applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If circular apertures are used in stacked diaphragms, then the structure is simple and easy to manufacture, but the ion beam cannot be effectively shaped and ions are not collected along the axis
Solution Approach 1:
The patent applies asymmetry by replacing circular apertures with non-circular apertures (rectangular, oval, or indented shapes) in the diaphragms. This asymmetric aperture design creates a non-uniform electric field distribution that actively shapes the ion beam and guides ions toward the central axis, resolving the limitation of circular apertures which produce symmetric fields that cannot effectively concentrate ions axially.
2Device complexity
If conventional stacked diaphragms are used, then the structure is simple, but active forward drive of ions is not achieved without complicated additional measures
Solution Approach 1:
The patent merges the ion guiding function and the ion forward drive function into a single integrated structure. The non-circular apertures in the stacked diaphragms simultaneously provide radial confinement (guiding ions along the axis) and, when combined with applied voltages, create axial electric field components that actively drive ions forward through the stack, eliminating the need for separate driving mechanisms.
Solution Approach 2:
The patent implements dynamics by applying time-varying voltages (RF and DC components) to the diaphragms with non-circular apertures. The RF voltage creates a dynamic pseudopotential well that confines ions radially, while the DC voltage gradient provides a static axial driving force, together creating a dynamic system that actively transports ions through the stack efficiently.
3Shape
If circular apertures with diminishing diameters are used, then the funnel shape is created, but ion distribution becomes uneven and space charge effects increase
Solution Approach 1:
The patent applies local quality by using non-circular apertures (such as rectangular or indented shapes) that create non-uniform electric field distributions across the aperture area. This local variation in field strength guides ions more uniformly through the stack, preventing the concentration of ions in specific regions and reducing space charge effects that arise from uneven ion distribution in circular aperture systems.
4Productivity
If non-circular apertures are used, then ion beam shaping and active forward drive are achieved, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the ion guide into multiple discrete diaphragm stages, each with non-circular apertures. This segmented structure allows the complex function of ion shaping and forward drive to be achieved through a series of simpler, identical modular units. Each diaphragm contributes to the overall ion guidance and transport, and the modular nature simplifies manufacturing and assembly compared to a monolithic complex structure.
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 approach enables efficient active forward drive and shaping of the ion beam, enhancing ion collection and mass selectivity, with a broader range of ion masses that can be guided, and reducing electrical capacitance, thus improving the performance of ion guides in mass spectrometry applications.
Implementation Method 1
Both phases of an RF voltage (several hundred kilohertz up to several megahertz; a few hundred volts) are applied alternately to the apertured diaphragms. This repels the ions from the inner funnel wall. The method of operation and the effect of this repelling pseudopotential are described in detail in the quoted patent specification, U.S. Pat. No. 5,572,035.
Implementation Method 2
In addition, a graded DC voltage (a few tens of volts in total) is applied to the apertured diaphragms to create a potential gradient along the axis of the stack of diaphragms. This forces the mobile ions through the highly rarefied gas in the ion funnel toward the exit hole.
Implementation Method 3
The internal space of the stack of diaphragms is filled with a damping gas. The diaphragm stack thus not only drives the ion beam actively forward, but is also able to shape its cross section. In combination with a damping and cooling gas in the diaphragm stack, the ions can be cooled and, in diaphragm stacks with suitable aperture shapes, can be collected in particular regions of the internal space.
Data Source
AI summary
The invention relates to RF voltage-operated ion guides based on stacked apertured diaphragms. The invention provides ion guides consisting of diaphragm stacks that permit the ion beam to be shaped in cross-section so that it corresponds to the acceptance profile of the subsequent section of the device, therefore yielding optimal ion transmission. For this purpose, at least some of the diaphragms in the diaphragm stacks do not have circular openings, but instead have openings which shape the cross section of the emerging ion beam in the desired manner. It is possible, for instance, to obtain elliptical beam cross sections, divided beams or beams focused to the shape of a fine thread at the output of the diaphragm stacks.