Electrostatic Aperture X-Ray Tube for Stable Microfocus Spots
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Solution Overview
Problem
Existing X-ray tubes with wound filaments face issues of inhomogeneous electron emission, leading to variations in focal spot size and shape, resulting in performance and longevity problems, especially at low anode voltages, due to geometric design and manufacturing tolerances, which affect the heat loading and service life of the target.
Innovation Solution
An X-ray tube design utilizing a flat electron emission surface with electrostatic apertures, including a control electrode, focusing electrode, and beam shaping electrode, allows for adjustable electron beam current density and focal spot shape without altering the cathode temperature or anode voltage, using electrostatic lenses to control the electron beam, eliminating the need for magnetic lenses and enabling flexible operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wound tungsten filaments are used as cathode, then electron emission is achieved, but inhomogeneous electron emission occurs leading to variations in focal spot size and shape
Solution Approach 1:
The invention extracts only the essential function of electron emission from the complex wound filament structure. By using a flat cathode surface with electrostatic control electrodes, the design removes the geometric complexities of wound filaments that cause inhomogeneous emission, achieving uniform electron extraction across the cathode surface through controlled electrostatic fields.
Solution Approach 2:
The invention changes the fundamental parameters of the cathode structure from wound filament geometry to flat surface geometry, and controls electron emission through electrostatic potential parameters rather than thermal parameters alone. This allows precise control of electron beam characteristics and achieves uniform focal spots through electrostatic lensing.
2Ease of operation
If magnetic lenses are used to focus electron beam, then focal spot control is achieved, but device complexity increases
Solution Approach 1:
The invention replaces the mechanical/magnetic lens system with an electrostatic field-based focusing mechanism. Control electrodes generate electrostatic fields that act as lenses to focus and shape the electron beam, eliminating the need for external magnetic lenses and their associated power supplies and control systems, thereby simplifying the overall device architecture.
3Adaptability or versatility
If low anode voltages are used, then certain applications are enabled, but power limitation occurs due to filament temperature constraints
Solution Approach 1:
The invention changes the operating parameters by decoupling electron emission control from thermal parameters alone and incorporating electrostatic control. This allows efficient electron extraction at lower temperatures, enabling low anode voltage operation with higher effective power output since the cathode does not need to be overheated to achieve sufficient electron emission.
4Measurement precision
If focal spot size is reduced to increase X-ray intensity, then resolution improves, but target heat loading increases quadratically
Solution Approach 1:
The invention applies local quality control through electrostatic lensing to achieve uniform electron beam distribution across the focal spot. By precisely controlling the electrostatic fields in the region between cathode and anode, the system can maintain small focal spot sizes for high resolution while ensuring uniform heat distribution on the target, preventing localized overheating and extending target life.
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 design provides a simpler, more efficient X-ray tube with improved homogeneity of electron beam distribution, allowing for stable and adjustable focal spots, increased power density, and extended service life of the target, while maintaining high X-ray intensity and resolution.
Implementation Method 1
a thermionic cathode having a flat electron emission surface
Implementation Method 2
a plurality of electrostatic electrodes... using electrostatic lenses to control the electron beam
Implementation Method 3
for generating an electron beam propagating from the cathode to the target... and for generating a microfocus spot on the target
Data Source
Figure 1
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AI summary
An x-ray tube (1), comprising - a thermionic cathode (4) having a flat electron emission surface (11), - and a target (6), wherein the x-ray tube (1) is designed for generating an electron beam (5) propagating from the cathode (4) to the target (6) along a beam axis (12) running along a z direction and for generating a microfocus spot (24) on the target (6), is characterized in that the target (6) is configured as a target anode (7), and that the x-ray tube (1) comprises apertures (16, 19, 22) in the form of a control electrode (14) with a first aperture opening (17), a focusing electrode (18) with a second aperture opening (20) and a beam shaping electrode (21) with a third aperture opening (23), the apertures (16, 19, 22) being located in z direction between the electron emission surface (11) and the target anode (7) in the named order, wherein the first aperture opening (17) is smaller than the emission surface (11) and has a contour which is rotationally symmetric with respect to the beam axis (12); wherein the second aperture opening (20) is larger than the first aperture opening (17) and has a contour which is rotationally symmetric with respect to the beam axis (12), wherein the third aperture opening (23) has a contour which is aligned with an xy plane and non-rotationally symmetric with respect to the beam axis (12), with x, y, z forming a Cartesian coordinate system (R). The X-ray tube (1) according to the invention has a simple structure for generating an electron beam (5), wherein the number of electrons in the electron beam (5) can be varied easily and over a wide range.