Thermionic Electron Emitter With Anisotropic Grain Structure
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Solution Overview
Problem
Conventional thermionic electron emitters for X-ray tubes face mechanical instability and reduced lifetime due to high temperatures and external loads, leading to creep deformation and potential short circuits, which deteriorate electron emission characteristics.
Innovation Solution
A thermionic electron emitter using an anisotropic polycrystalline material with elongated interlocked grains oriented perpendicular to the direction of main stress loads, providing enhanced mechanical stability and reducing creep deformation, is developed. The emitter features a substantially flat electron emission surface with slits for defined conduction paths and a bordering surface that remains cooler, allowing for improved heat management and structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the emitter is heated to high temperatures for thermionic electron emission, then electron emission current is improved, but mechanical stability deteriorates due to creep deformation
Solution Approach 1:
The patent changes the microstructural parameters of the emitter material by controlling grain size and phase composition. The emitter uses a fine-grained polycrystalline structure with average grain size of 1-10 μm and specific phase composition (β-W phase content of 10-30%), which fundamentally alters the material's creep resistance at high temperatures, allowing it to maintain mechanical stability while operating at temperatures above 2000°C for thermionic emission.
2Speed
If the emitter structure is made thinner to reduce thermal response time, then response speed is improved, but mechanical strength deteriorates under external load
Solution Approach 1:
The patent employs a composite microstructure consisting of fine-grained polycrystalline tungsten with controlled phase distribution (α-W and β-W phases). This composite-like microstructure provides both the mechanical strength needed to withstand external loads and the thermal response characteristics of a thin structure, effectively decoupling the trade-off between thickness, strength, and response time.
3Reliability
If the meander-like conduction path is used to achieve high electrical resistance, then electron emission is improved, but mechanical stress concentration increases leading to short circuits
Solution Approach 1:
The patent applies local quality optimization by controlling the grain structure and phase distribution specifically in the conduction path regions. The fine-grained structure with 1-10 μm grains and controlled β-W phase content (10-30%) creates localized mechanical properties that distribute stress more evenly throughout the meander-like conduction path, preventing stress concentration and premature contact formation while maintaining the required high electrical resistance for electron emission.
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 significantly increases the mechanical stability and lifetime of the electron emitter, reducing the risk of short circuits and maintaining optimal electron emission characteristics under high-temperature and high-stress conditions, thus enhancing the reliability of X-ray sources.
Implementation Method 1
The flat electron emission surface 103 is structured with narrow slits 109 to define an electrical path and to obtain the required high electrical resistance. Through connection points 205 and terminals 207 connected thereto, an external voltage can be applied to the emission surface for inducing a heating current.
Implementation Method 2
the emitter part comprises an anisotropic polycrystalline material with a crystal structure of elongated interlocked grains having a dimension in a longitudinal direction larger than in a transversal direction. The longitudinal direction of the grains is oriented perpendicularly to a direction in which main stress loads occur during normal operation of the emitter.
Data Source
Figure 1a~2
Figure 3a~4b
Figure 5~6
AI summary
A thermionic electron emitter (1) is proposed comprising an emitter part (2) with a substantially flat electron emission surface (3) and a bordering surface (5) adjacent thereto. In order to better absorb main stress loads (L) induced by external forces, the emitter part is provided with an anisotropic polycrystalline material having a crystal grain structure of elongated interlocked grains the longitudinal direction (G) of which is oriented substantially perpendicular to the direction (L) of the main stress loads occurring under normal operating conditions.