Ion Source Virtual Cathode for Soft Electron Ionization
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Solution Overview
Problem
Existing electron ionization (EI) sources face challenges in generating a stable high-intensity electron beam at low electron energies, which limits their ability to produce rich molecular ions and high-mass diagnostic ions necessary for structure elucidation and identification of unknown compounds.
Innovation Solution
The design includes an ion source with an electron extractor, thermionic cathode, and electron lens, which decelerates electrons to form a virtual cathode, allowing for the acceleration of a high-intensity electron beam into the ionization chamber, even at low electron energies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If low electron energy (8-20 eV) is used for soft ionization, then molecular ions and high-mass diagnostic ions are enhanced, but electron beam intensity becomes too low
Solution Approach 1:
The electron beam path is segmented into multiple sections with different voltage conditions: an initial acceleration region, a deceleration region with the electron lens creating a potential valley, and a final acceleration region into the ionization chamber. This allows the electron beam to be built up, slowed down to form the virtual cathode, then accelerated again to maintain high intensity at low energy.
Solution Approach 2:
A virtual cathode is introduced as an intermediary structure between the electron source and the ionization chamber. This virtual cathode, formed by the potential valley, serves as an intermediate electron reservoir that enables the electron beam to maintain high intensity while operating at low energy (8-20 eV), thereby producing enhanced molecular ions without sacrificing beam intensity.
2Quantity of substance
If low electric field strength is applied between filament and ionization chamber, then soft ionization is achieved, but electron beam stability deteriorates
Solution Approach 1:
The system dynamically adjusts electron energy through a multi-stage voltage application process. The electron lens creates a time-dependent potential valley that decelerates electrons to form the virtual cathode, then allows them to be re-accelerated. This dynamic voltage control enables stable electron beam operation at low energy, achieving both soft ionization and beam stability.
Solution Approach 2:
The voltage parameters are changed in a specific sequence: first applying voltage to accelerate electrons from the filament, then applying a retarding voltage at the electron lens to create the potential valley and virtual cathode, and finally applying extraction voltage to accelerate electrons into the ionization chamber. These parameter changes enable stable low-energy operation while maintaining high electron beam intensity.
3Power
If conventional EI source configuration is used, then high electron beam intensity is achieved, but soft ionization capability is limited
Solution Approach 1:
The electron lens serves multiple functions: it focuses the electron beam, creates the potential valley for deceleration, and forms the virtual cathode. This multi-functional component enables the ion source to achieve both high electron beam intensity and soft ionization capability, making the system versatile for different ionization requirements.
Solution Approach 2:
The virtual cathode formed by the electron lens acts as an intermediary that couples the high-intensity electron beam with the low-energy ionization process. This intermediary structure allows the system to maintain high electron beam intensity while delivering soft ionization (8-20 eV) to the sample, thereby achieving both high power and soft ionization capability simultaneously.
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 configuration enhances the production of molecular ions and high-mass diagnostic ions, improving the soft ionization process and increasing the intensity of sample signals, facilitating better structural elucidation and tandem mass spectrometry experiments.
Implementation Method 1
An electron emitter, typically a thermionic cathode such as a heated filament composed of a refractory material (e.g., tungsten), is employed to emit energetic electrons.
Implementation Method 2
a potential valley is formed at the electron lens that serves to decelerate the electrons and form at the electron lens a virtual cathode comprising the decelerated electrons
Implementation Method 3
Ionization of the sample material occurs as a result of the electron beam bombarding the sample material in the region where the sample and electron paths intersect. The primary reaction of the ionization process may be described by the following relation: M+e−→M*++2e−
Data Source
AI summary
An ion source is configured for soft electron ionization and produces a low electron-energy, yet high-intensity, electron beam. The ion source includes an electron source that produces the electron beam and transmits it into an ionization chamber. The electron beam interacts with sample material in the ionization chamber to produce an ion beam that may be transmitted to a downstream device. The electron source is configured for generating a virtual cathode upstream of the ionization chamber, which enhances the intensity of the electron beam.