Curved Cathode Assembly for X-ray Tube Beam Laminarity
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Solution Overview
Problem
Long throw lengths in x-ray tubes lead to non-laminar electron beams, resulting in unacceptable focal spots and difficulties in producing useful x-rays, as electrons become less laminar and collide with the anode in an unpredictable manner.
Innovation Solution
A cathode assembly with a curved emitting surface that produces an electron beam with a y-dimension greater than an x-dimension, which accelerates through an acceleration region and drifts through a corresponding drift region, ensuring the electron beam remains laminar and impinges on the anode with a focal spot having a y-dimension less than an x-dimension, thereby maintaining beam stability and focus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the throw length is lengthened to decrease back ion bombardment and evaporation, then the anode material protection is improved, but the electron beam becomes less laminar resulting in unacceptable focal spot
Solution Approach 1:
The electron emitter employs a curved emitting surface with a specific radius of curvature (e.g., 0.5 to 2.0 times the throw length) to shape the electron beam. This curvature transforms the initially non-laminar electron trajectories into a laminar beam that maintains focus over the extended throw length, resolving the contradiction between long throw length benefits and focal spot quality degradation.
Solution Approach 2:
The invention changes the geometric parameter of the emitting surface from flat to curved, and specifically optimizes the radius of curvature relative to the throw length. This parameter change enables the electron beam to maintain laminar flow characteristics over the extended throw length, simultaneously achieving both anode protection and acceptable focal spot quality.
2Object-generated harmful factors
If the throw length is lengthened, then back ion bombardment and evaporation are decreased, but the electron beam laminarity deteriorates
Solution Approach 1:
The curved emitting surface with optimized radius of curvature shapes the electron beam to maintain laminar flow. The curvature radius is specifically selected (0.5 to 2.0 times the throw length) to ensure that electrons emitted across the surface converge to form a stable, laminar beam that resists disruption over the extended throw length, thereby maintaining beam stability while reducing harmful back ion bombardment.
Solution Approach 2:
By changing the emitting surface geometry parameter (curvature radius) and optimizing it relative to the throw length, the invention maintains electron beam laminarity despite the extended throw length. This parameter optimization ensures the beam remains stable and coherent, preventing the deterioration that would normally occur with longer throw lengths.
3Device complexity
If a flat emitting surface is used, then the device structure is simple, but the electron beam dimensions cannot be transposed to achieve acceptable focal spot in long throw length tubes
Solution Approach 1:
The curved emitting surface with a radius of curvature optimized for the throw length transforms the electron beam dimensions during acceleration. The curvature causes electrons from different parts of the emitting surface to converge, transposing the beam dimensions (swapping x and y dimensions) to produce an acceptable focal spot. This geometric solution achieves the dimensional transformation without requiring complex additional optical elements.
Solution Approach 2:
The curved emitting surface utilizes the third dimension (curvature radius) to control electron beam behavior. By introducing this geometric dimension, the invention achieves dimensional transposition of the electron beam, transforming a wide beam at the emitter into a focused beam at the anode, thereby achieving acceptable focal spot dimensions without excessive device complexity.
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 ensures a stable and laminar electron beam impinges on the anode, producing a focused x-ray spot with dimensions transposed between the cathode and anode, effectively addressing the issue of non-laminar beams and improving x-ray production in long throw length x-ray tubes.
Implementation Method 1
applying an electrical current to a cathode to cause electrons to be emitted from the cathode by thermionic emission
Implementation Method 2
The acceleration region is configured such that when the electron beam propagates within the acceleration region, the electron beam accelerates in a z-direction substantially normal to a midpoint of the curved emitting surface
Implementation Method 3
The drift region is configured such that the combined lengths of the drift region and the acceleration region are sufficient for the y-dimension to be less than the x-dimension at the anode
Implementation Method 4
In Bremsstrahlung, electrons emitted from the cathode decelerate when deflected by nuclei of the anode. The decelerating electrons lose kinetic energy and thereby produce x-rays
Implementation Method 5
X-ray fluorescence occurs when an electron colliding with material of the anode has sufficient energy to knock an orbital electron of the anode out of an inner electron shell. Other electrons of the anode in outer electron shells fill the vacancy left in the inner electron shell. As a result of the electron of the anode moving from the outer electron shell to the inner electron shell, X-rays of a particular frequency are produced
Data Source
AI summary
Cathode assembly for a long throw length x-ray tube. In one example embodiment, a cathode assembly for an x-ray tube includes an electron emitter, an acceleration region, and a drift region. The electron emitter includes a curved emitting surface configured to emit an electron beam having a y-dimension that is greater than an x-dimension at the electron emitter. The acceleration region is defined adjacent to the electron emitter. The acceleration region is configured such that when the electron beam propagates within the acceleration region, the electron beam accelerates in a z-direction substantially normal to a midpoint of the curved emitting surface. The drift region is defined between the acceleration region and an anode. The drift region is configured such that the combined lengths of the drift region and the acceleration region are sufficient for the y-dimension to be less than the x-dimension at the anode.