Segmented EI Filament for Uniform Electron Emission
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Solution Overview
Problem
Cylindrically symmetric electron impact ion sources in mass spectrometers face issues with ion beam losses and non-uniform electron emission due to filament deformation during heating and cooling cycles, as classical ring-shaped filaments lose shape and exhibit varying electron emission characteristics.
Innovation Solution
A cathode system with a filament divided into segments by current supply posts, where each post supplies or returns current to multiple segments, maintaining a consistent temperature and electron emission through spot welding, ablation, and specialized electric circuits, using materials like Tungsten, thoriated Tungsten, or Yttrium/Rhenium alloys, and resilient posts to minimize heat loss and ensure uniform electron emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a ring-shaped filament is used to generate a cylindrically symmetric electron beam, then the ion beam symmetry is improved and matches modern mass spectrometer requirements, but the filament loses shape after repeated heating and cooling cycles leading to non-uniform electron emission
Solution Approach 1:
The filament is divided into multiple independent segments (e.g., 3-6 segments) arranged in a ring or helical configuration. Each segment is electrically isolated and can be controlled independently through separate current supply posts, allowing the overall cylindrical symmetry to be maintained even if individual segments experience thermal deformation
Solution Approach 2:
The filament structure transitions from a rigid continuous ring to a dynamic segmented configuration where each segment can independently adjust its electron emission characteristics. This dynamic control allows compensation for thermal deformation by adjusting current distribution among segments to maintain uniform overall electron emission
2Stability of the object's composition
If additional support posts are added to reduce filament deformation, then the shape stability is improved, but heat is carried away via the posts leading to non-uniform temperature distribution
Solution Approach 1:
Instead of adding support posts to a continuous filament, the filament is segmented into multiple sections. Each segment is supported and electrically connected through its own posts, distributing the thermal load and reducing heat conduction paths that would cause temperature non-uniformity
Solution Approach 2:
Each filament segment has its own electrical connection and current supply characteristics, allowing local temperature and emission control. The current supply posts are configured to provide appropriate current to each segment based on its specific thermal conditions, maintaining overall uniformity despite local variations
3Reliability
If the filament is divided into segments with separate current supply, then the electron emission uniformity is improved, but the device complexity increases
Solution Approach 1:
The current supply posts serve multiple functions: they provide electrical connection to filament segments, act as mechanical support structures, and enable independent current control for temperature compensation. This multi-functionality reduces the need for separate components and manages the complexity through integrated design
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
The solution provides a stable, cylindrically symmetric electron beam with consistent electron emission along the filament, reducing ion beam losses and maintaining performance over a wide temperature range, optimizing ion source efficiency and matching modern mass spectrometer requirements.
Implementation Method 1
a cathode system for an EI source comprises a filament and a plurality of current supply posts (electrically) dividing the filament into a plurality of segments and each current supply post supplying or returning the electric current for at least two segments of the filament
Implementation Method 2
each current supply post supplying or returning the electric current for at least two segments of the filament
Data Source
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AI summary
The invention provides a cathode system for an Electron Ionization (EI) source comprising a filament and current supply posts, the current supply posts dividing the filament into segments and each current supply post supplying or returning the current for at least two segments of the filament. Each filament segment is connected, for instance by spot welding, to the supply posts delivering the heating current. The filament segments may be arranged in a row, or substantially parallel to each other. Filament segments arranged in a row may form a closed loop, for instance, a ring. Other embodiments encompass the filament shape of a helical coil.