Electron Beam Control Using Pulse Width Modulation
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Solution Overview
Problem
Conventional CT systems face challenges in rapidly controlling electron beam emission and focusing due to slow filament heating, leading to issues with electron beam positioning and imaging quality, especially at low currents where electro-magnetic forces cause beam constriction, hindering precise control and image quality.
Innovation Solution
The implementation of a method and system using pulse width modulation (PWM) to modulate the duty cycle of the electron beam, allowing for microsecond current control and wide range focusable emission, with a control unit identifying current configurations and adjusting the electron beam intensity using electrodes and magnetic assemblies to maintain focus and position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional filament heating is used to control electron beam emission, then electron beam intensity can be controlled, but the response time is slow (tens of milliseconds) preventing fast emission control
Solution Approach 1:
The patent extracts the electron beam emission control function from the slow filament heating mechanism by introducing a separate, fast-response electrostatic grid system. The grid can rapidly modulate the electron beam current independently of the filament heating state, enabling microsecond-scale emission control while the filament maintains a steady heating condition.
Solution Approach 2:
The electrostatic grid acts as an intermediary between the control system and the electron beam. By placing the grid between the filament and the electron beam path, it provides a fast-response interface for beam current modulation without directly controlling the filament heating, thus decoupling the slow thermal process from the fast beam control requirement.
2Speed
If rapid changes in electron beam current are made using electrostatic grid or magnetic assembly, then electron beam intensity can be quickly controlled, but proper positioning and focusing of the electron beam is prevented
Solution Approach 1:
The patent segments the electron beam control functions into distinct components: the electrostatic grid handles rapid intensity modulation, while separate focusing electrodes and magnetic assemblies maintain beam positioning and focusing. This functional segmentation allows each component to optimize its specific task without interfering with others.
Solution Approach 2:
Different regions of the electron beam path are given different control characteristics. The grid region provides fast intensity modulation, while the focusing region maintains stable electro-magnetic fields for precise beam positioning. Each region is optimized for its specific function, allowing rapid current changes without compromising focus precision.
3Adaptability or versatility
If electron beam current is modulated from 0% to 100% intensity, then full dynamic range control is achieved, but space charge force changes cause electron repulsion and affect focal spot size
Solution Approach 1:
The patent implements dynamic compensation for space charge effects by continuously adjusting the electrostatic grid voltage in response to changes in beam current. As the beam current varies across the full dynamic range, the grid voltage is dynamically modulated to maintain consistent electron trajectories and focal spot characteristics, counteracting the space charge repulsion that would otherwise cause focal spot size variations.
4Object-affected harmful factors
If X-ray tube operates with low electron beam current (10 mA), then patient dose is reduced, but electro-magnetic forces overly focus the electron beam forming a constricted waist, hindering precise control
Solution Approach 1:
The patent applies preliminary anti-action by using the electrostatic grid to pre-compensate for the excessive focusing effect of electro-magnetic fields at low currents. Before the electron beam reaches the region where electro-magnetic forces would cause constricted waist formation, the grid voltage is adjusted to create an opposing electrostatic field that counteracts the over-focusing, thereby maintaining precise beam control even at low currents that reduce patient dose.
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 approach enables precise control of electron beam intensity and focus, enhancing imaging system performance and image quality while reducing radiation effects and prolonging X-ray tube life, allowing for high-quality imaging across a wide dynamic range of emission.
Implementation Method 1
generating an electron beam in an X-ray tube
Implementation Method 2
a current configuration corresponding to a particular view of the imaging system is identified. If the identified current configuration is within a determined range, a duty cycle of the electron beam for the particular view of the imaging system is modulated
Implementation Method 3
The changes in the space charge force further affect the electro-magnetic focusing and deflection of the electron beam in the X-ray tube
Implementation Method 4
a duty cycle of the electron beam for the particular view of the imaging system is modulated using pulse width modulation
Data Source
AI summary
A method for operating an electron beam system is presented. Further, an electron beam system, an X-ray tube and a CT system that implement the presented method are also described. The method includes generating an electron beam in an X-ray tube in an imaging system. Additionally, a current configuration corresponding to a particular view of the imaging system is identified. If the identified current configuration is within a determined range, a duty cycle of the electron beam for the particular view of the imaging system is modulated using pulse width modulation. Further, the modulated electron beam is focused towards a target.