Electron Gun Anode Voltage for Ion Repulsion
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Solution Overview
Problem
Electron microscopes and three-dimensional additive manufacturing apparatuses face ion bombardment issues due to the lack of an ion reflector, which can damage the cathode and complicate the electron gun configuration when trying to prevent positive ions from reaching it.
Innovation Solution
An electron gun design that includes a cathode, grid, and anode with a positive anode voltage, where the grid converges thermions and the anode repels secondary electrons and ionized gas, reducing ion bombardment by taking in secondary electrons and repelling positive ions with its positive potential, thus acting like an ion reflector without the need for additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a repeller electrode is added to the electron gun to prevent ion bombardment, then ion bombardment damage is reduced, but the configuration of the electron gun becomes complicated
Solution Approach 1:
The anode is made to serve dual functions: extracting electrons to form the electron beam and simultaneously repelling positive ions to prevent ion bombardment damage to the cathode. By controlling the anode voltage to be positive, the anode automatically performs the ion repulsion function without requiring an additional repeller electrode, thus protecting the cathode while keeping the electron gun configuration simple.
Solution Approach 2:
The anode is designed to perform multiple functions: (1) extract thermions from the cathode to form the electron beam, (2) control the electron beam current through voltage adjustment, and (3) repel positive ions to prevent ion bombardment. This multi-functional design eliminates the need for separate components and simplifies the overall electron gun structure.
2Productivity
If the anode voltage is increased to improve electron beam extraction, then electron beam current increases, but ion bombardment damage worsens
Solution Approach 1:
The anode voltage is controlled to be positive (higher than the cathode potential), which simultaneously achieves two objectives: (1) enhances electron beam extraction and current by creating a stronger electric field for electron acceleration, and (2) repels positive ions away from the cathode by creating a potential barrier. This parameter optimization resolves the contradiction by finding a voltage setting that benefits both electron extraction and ion repulsion.
Solution Approach 2:
The positive anode voltage, which could potentially accelerate ions toward the cathode and cause damage, is instead utilized to repel ions away from the cathode. By inverting the expected harmful effect and using the electric field to push ions away rather than pull them in, the same voltage that drives electron extraction also provides cathode protection against ion bombardment.
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
Prevents ion bombardment of the cathode by effectively repelling positive ions and reducing secondary electron emission, simplifying the electron gun configuration and reducing damage, while maintaining the functionality of an ion reflector without increasing manufacturing costs.
Implementation Method 1
a cathode that is heated to emit thermions
Implementation Method 2
a grid that has a first aperture formed therein along a central axis of a tip of the cathode and that has a grid voltage applied thereto, the grid voltage having a potential lower than that of the cathode, wherein the grid converges the thermions passing through the first aperture by the grid voltage applied thereto
Implementation Method 3
an anode that has a second aperture formed therein along the central axis and that has an anode voltage applied thereto, wherein the anode causes the thermions extracted from the cathode to pass through the second aperture as an electron beam by the anode voltage applied thereto
Data Source
AI summary
An electron gun includes a cathode that is heated to emit thermions; a cathode heating power supply that supplies a cathode heating current for heating the cathode; a grid that has a first aperture formed therein and that has a grid voltage applied thereto, the grid voltage having a potential lower than that of the cathode, wherein the grid converges the thermions passing through the first aperture by the grid voltage; an anode that has a second aperture formed therein and that has an anode voltage applied thereto, wherein the anode causes the thermions extracted from the cathode to pass through the second aperture as an electron beam by the anode voltage; an anode-voltage power supply that applies the anode voltage to the anode; and a controller that causes the anode voltage having a positive potential to be applied from the anode-voltage power supply to the anode.