Open-Pored Electrode Surface for TWT Secondary Electron Emission
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Solution Overview
Problem
Vacuum electron beam assemblies face challenges in minimizing secondary electron emission, which can disrupt the desired functionality of electron beam tubes, particularly in structures like traveling wave tubes where secondary electrons can interfere with the primary electron beam.
Innovation Solution
An open-pored surface layer is created on the electrode, with a multiplicity of cavities connected in a coherent framework, where pores have similar dimensions and a significant proportion of pore openings face directly to the surface, along with undercuts on edge sections, reducing secondary electron emission. This is achieved through a composite material structure of molybdenum and copper, where copper is selectively removed using electropolishing or other processes to form a porous surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a smooth electrode surface is used, then manufacturing is simple, but secondary electron emission is high
Solution Approach 1:
The electrode surface is transformed into a porous structure with controlled pore sizes (1-10 μm) and specific geometries. This porous configuration reduces secondary electron emission by preventing secondary electrons from escaping the surface, while the pores are filled with solder material to maintain vacuum tightness. The porous structure is achieved through controlled dissolution of a sacrificial component in a composite material system.
Solution Approach 2:
The electrode is constructed as a composite material consisting of a base material (e.g., molybdenum or tungsten) and a sacrificial material (e.g., copper or nickel) with different dissolution rates. The sacrificial material is distributed throughout the base material and is selectively removed to create the porous surface structure. This composite approach enables precise control over pore formation while maintaining the mechanical and thermal properties of the base material.
2Object-generated harmful factors
If a porous surface structure is created to reduce secondary electron emission, then harmful emission is reduced, but vacuum tightness may be compromised
Solution Approach 1:
The solder material acts as an intermediary substance that fills the porous structure on the electrode surface. This solder material serves dual functions: it seals the pores to maintain vacuum tightness while also contributing to the low secondary electron emission properties. The solder is introduced in liquid or paste form and then solidified to create a vacuum-tight seal over the porous structure.
3Object-generated harmful factors
If a porous surface layer is formed, then secondary electron emission is reduced, but manufacturing complexity increases
Solution Approach 1:
The porous structure is created through a preliminary action of incorporating a sacrificial material into the electrode during manufacturing, followed by selective removal. This approach simplifies the overall process compared to attempting to create porous structures through direct methods, as the sacrificial material self-organizes into a distributed network that can be uniformly removed to create consistent pore structures throughout the electrode surface.
4Object-generated harmful factors
If the surface is roughened to reduce secondary electron emission, then emission is reduced, but thermal conductivity may be affected
Solution Approach 1:
The electrode structure is designed with local quality differentiation: the bulk material maintains high density and excellent thermal conductivity, while only the surface layer (depth of 10-100 μm) is transformed into a porous structure. This localized modification ensures that secondary electron emission is reduced at the surface while the thermal conductivity of the electrode bulk remains unaffected, as the porous structure is confined to a thin surface layer.
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 open-pored structure significantly reduces secondary electron emission compared to smooth surfaces, maintaining vacuum tightness and thermal conductivity while allowing precise machining and reliable soldering, making it suitable for applications like traveling wave tubes.
Implementation Method 1
The secondary electrons are created, for example, by the impact of primary electrons on an electrode located in the area of movement of the primary electrons
Implementation Method 2
copper is selectively removed using electropolishing or other processes to form a porous surface
Data Source
Figure 1~2(F)
Figure 3(A)~3(C)
Figure 4(A)~4(B)
AI summary
In order to reduce the secondary electron emission in a vacuum electron beam arrangement, in particular a travelling wave tube (TWT), a surface structure with an open-pore surface layer (OS) and a method for producing such a surface structure are described.