Electron Gun Vacuum Layout for Stable Emission Current
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Solution Overview
Problem
Existing charged particle beam devices face contamination of the electron source due to impurities discharged by non-evaporable getter materials during activation, leading to unstable emission currents.
Innovation Solution
A charged particle beam device is designed with a configuration that includes a single crystal needle, filament, insulator, non-evaporable getter material, extraction electrode, vacuum vessel, and shields to maintain a high vacuum and prevent contamination of the electron source by impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-evaporable getter material is installed inside the electron gun to lower pressure, then vacuum quality is improved, but impurities are discharged during activation causing contamination of the electron source
Solution Approach 1:
The electron gun is divided into two separate vacuum chambers: a first vacuum chamber containing the electron source and NEG material, and a second vacuum chamber containing other electron gun components. This segmentation isolates the contamination source (NEG material) from the electron source while maintaining differential vacuum levels, resolving the contradiction between achieving low pressure and preventing contamination.
Solution Approach 2:
A differential pumping system acts as an intermediary between the first and second vacuum chambers, maintaining different pressure levels in each chamber. This allows the NEG material to operate in a lower pressure environment for effective gas absorption while preventing impurities from reaching the electron source, which operates in a slightly higher but still high-vacuum environment.
2Reliability
If pressure around electron source is reduced to stabilize emission current, then emission stability is improved, but activation of NEG material discharges impurities to surroundings
Solution Approach 1:
The NEG material is extracted from the general electron gun environment and placed specifically within the first vacuum chamber, separated from the electron source by the chamber wall and differential pumping system. This extraction allows the NEG material to perform its pressure-reducing function while isolating its harmful byproduct (impurity discharge) from the electron source.
Solution Approach 2:
The design accepts that the NEG material will discharge impurities during activation and requires periodic replacement or reactivation. The system is designed to handle this temporary contamination event by isolating it spatially and temporally from the electron source, allowing the NEG material to be replaced or reactivated without damaging the electron source.
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 device stabilizes emission current by efficiently reducing pressure around the electron source, preventing contamination and maintaining consistent performance.
Implementation Method 1
the NEG material absorbs a gas while maintaining its shape without evaporating, and serves as a pump for performing evacuation
Implementation Method 2
a vacuum vessel that includes a heater for heating the non-evaporable getter material
Implementation Method 3
a shield that is disposed to shield a straight line connecting the single crystal needle, the filament, and the insulator to the non-evaporable getter material
Data Source
AI summary
The invention provides a charged particle beam device that prevents an electron source from being contaminated and stabilizes an emission current by efficiently reducing the pressure around the electron source. The charged particle beam device includes an electron source that includes a single crystal needle, a filament connected to the single crystal needle, and an insulator that holds the filament, a non-evaporable getter material, an extraction electrode that includes the electron source, holds the non-evaporable getter material, and has a vacuum inside, a vacuum vessel that includes a heater for heating the non-evaporable getter material and the extraction electrode disposed therein, and maintains a vacuum with a pressure higher than that of the vacuum of the extraction electrode, and a shield that is disposed to shield a straight line connecting the single crystal needle, the filament, and the insulator to the non-evaporable getter material, and is connected to the extraction electrode.