Segmented X-ray Tube Filament Assembly for Fast Thermal Switching
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Solution Overview
Problem
Existing x-ray tube filaments face challenges in achieving fast switching times due to their thermal response, or thermal time constant, which is related to the time required for the filament to cool and reduce electron emission, leading to increased risks of electrical arcing and damage, especially at high voltages.
Innovation Solution
The use of a filament assembly with multiple, short segments thermally connected in parallel to heat sinks, configured for simultaneous electron emission, and electrically connected in series or parallel, with reduced wire diameter and carburized thoriated tungsten to control power dissipation and electrical impedance, enhancing thermal and electrical efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional filament structure is used, then the filament can maintain stable electron emission, but the thermal time constant is large resulting in slow switching time
Solution Approach 1:
The filament is divided into multiple discrete segments (first filament segment, second filament segment, third filament segment) that are thermally isolated from each other by non-conductive spacers. This segmentation reduces the thermal mass of each individual filament segment, thereby reducing the thermal time constant and enabling faster switching times while maintaining stable electron emission from each segment
Solution Approach 2:
Non-conductive spacers are introduced as intermediary elements between adjacent filament segments. These spacers provide thermal isolation that prevents heat accumulation across the entire filament structure, reducing the overall thermal time constant while the filament segments continue to emit electrons stably when heated
2Use of energy by moving object
If the filament wire diameter is increased to reduce electrical impedance, then electrical efficiency improves, but thermal mass increases resulting in slower cooling and longer switching time
Solution Approach 1:
The filament is segmented into multiple smaller-diameter wires (each approximately 0.020 inches in diameter) rather than using a single thick wire. This segmentation reduces the thermal mass of each individual conductor while the parallel arrangement of multiple segments maintains sufficient electrical conductivity and low impedance for efficient power transmission
Solution Approach 2:
Multiple thin filament segments are electrically connected in parallel between common endpoints (first endpoint and second endpoint), combining their electrical conductance to achieve low overall impedance while each individual segment maintains low thermal mass for fast switching response
3Productivity
If high voltage is applied to accelerate electrons, then x-ray production efficiency increases, but the risk of electrical arcing from tube structures to the filament increases
Solution Approach 1:
The filament structure is segmented into multiple isolated segments that reduce the overall thermal mass and allow for more uniform heating. This enables faster cycling and better control of electron emission, reducing the likelihood of uncontrolled arcing when high voltages are applied to accelerate electrons for x-ray production
Solution Approach 2:
The filament operating parameters are optimized by using multiple segments with reduced individual thermal mass, allowing for precise control of electron emission. This enables the system to handle high accelerating voltages more reliably by preventing excessive electron emission that could lead to arcing between tube structures and the filament
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 configuration reduces the thermal time constant, resulting in faster switching times, improved mechanical ruggedness, and controlled power dissipation and electrical impedance, enabling more efficient and reliable operation of x-ray tubes.
Implementation Method 1
an electric current is supplied to the cathode filament, causing it to emit a stream of electrons by virtue of a process known as thermionic emission
Implementation Method 2
each filament segment includes first and second end portions that are in thermal communication with the heat sink
Data Source
AI summary
A filament assembly for use in an x-ray emitting device or other filament-containing device is disclosed. In one embodiment, an x-ray tube is disclosed, including a vacuum enclosure that houses both an anode having a target surface, and a cathode positioned with respect to the anode. The cathode includes a filament assembly for emitting a beam of electrons during tube operation. The filament assembly comprises a heat sink and a plurality of filament segments. The filament segments are configured for simultaneous emission of an electron beam for impingement on the target surface of the anode, and are electrically connected in series. Each filament segment includes first and second end portions that are thermally connected to the heat sink, and a central portion that can be configured with a modified work function for preferential electron emission.