Photocathode Electron Gun Anode Structure for Space Charge Control
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Solution Overview
Problem
The space charge effect in pulsed electron beams leads to coulomb repulsion among electrons, causing trajectory and energy distribution changes in the electron beam, resulting in decreased brightness and increased energy width, which complicates achieving high spatial and temporal resolution in electron beam applications.
Innovation Solution
An electron gun configuration is introduced, featuring a photocathode with a substrate and photoelectric film, a pulsed excitation light source, and a unique anode electrode structure with a recessed and protruding shape to control the surface electric field intensity, thereby mitigating the space charge effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of electrons included in one pulse of a pulsed electron beam is increased, then the measurement signal is sufficient, but the electrons occur coulomb repulsion with each other to change trajectory and energy distribution, resulting in decreased brightness and increased energy width
Solution Approach 1:
The anode electrode is divided into a first anode electrode and a second anode electrode with different functions. The first anode electrode extracts electrons from the photocathode, while the second anode electrode accelerates the electron beam. This segmentation allows independent optimization of electron extraction and acceleration, reducing space charge effects while maintaining sufficient electron quantity per pulse.
Solution Approach 2:
The first anode electrode is positioned close to the photocathode to create a strong local electric field for efficient electron extraction. The second anode electrode is positioned further away to provide gradual acceleration. This local quality differentiation optimizes the electric field distribution, minimizing coulomb repulsion effects while ensuring sufficient electron beam intensity.
2Loss of time
If the pulse width is shortened to achieve high temporal resolution, then the time resolution is improved, but the space charge effect becomes more obvious, causing deterioration in brightness
Solution Approach 1:
The first anode electrode is positioned immediately adjacent to the photocathode to establish a strong extraction field before the electron pulse fully forms. This preliminary action of electron extraction creates a well-defined electron source that reduces subsequent space charge effects during the short pulse duration, enabling high temporal resolution without brightness deterioration.
3Quantity of substance
If a single-shot measurement is performed with sufficient electrons to obtain a measurement signal for irreversible processes, then the measurement signal is sufficient, but the spatial resolution is deteriorated due to the space charge effect
Solution Approach 1:
By segmenting the anode into extraction and acceleration electrodes, the patent enables sufficient electron quantity to be generated at the photocathode while the accelerated beam maintains low divergence. This results in both sufficient measurement signal and high spatial resolution in single-shot measurements.
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 effectively prevents the deterioration of electron beam brightness due to the space charge effect, enabling high temporal and spatial resolution measurements in electron beam applications.
Implementation Method 1
a photocathode including a substrate and a photoelectric film formed on the substrate; a light source configured to emit a pulsed excitation light
Implementation Method 2
a second power supply configured to apply an acceleration voltage between the photocathode and the second anode electrode
Data Source
AI summary
The apparatus includes: a photocathode including a substrate and a photoelectric film formed on the substrate; a light source configured to emit a pulsed excitation light; a condenser lens facing the substrate of the photocathode and configured to condense the pulsed excitation light toward the photocathode; a first anode electrode and a second anode electrode facing the photoelectric film of the photocathode; a first power supply configured to apply a first control voltage between the first anode electrode and the second anode electrode; and a second power supply configured to apply an acceleration voltage between the photocathode and the second anode electrode. The first anode electrode is disposed between the photocathode and the second anode electrode. A surface of the first anode electrode facing the second anode electrode has a recessed shape, and a surface of the second anode electrode facing the first anode electrode has a protruding shape.