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Two-dimensional space-charge-limited emission: beam-edge characteristics and applications
1Air Force Research Laboratory, Directed Energy Directorate, Kirtland Air Force Base, New Mexico 87117, USA.
Physical Review Letters
|October 3, 2001
Summary
Researchers explored 2D electron emission, finding higher current densities near beam edges than predicted by Child-Langmuir theory. This discovery has implications for electron emission from cathodes with abundant free electrons.
Area of Science:
- Plasma Physics
- Electron Emission Dynamics
- Semiconductor Device Physics
Background:
- Child-Langmuir law describes space-charge-limited current in 1D planar diodes.
- Extending this law to 2D and higher dimensions remains analytically challenging.
- Understanding 2D emission is crucial for advanced electron sources.
Purpose of the Study:
- Investigate 2D electron emission characteristics in planar diodes.
- Analyze the transition region between electron beams and vacuum.
- Identify and characterize regions of enhanced current density.
Main Methods:
- Utilized a 2D finite element, electrostatic ray-tracing code.
- Simulated electron emission in a planar diode geometry.
- Examined current density distributions, particularly near beam edges.
Main Results:
- Observed current densities exceeding Child-Langmuir predictions near beam edges.
- Identified and characterized "wings" of increased current density.
- These phenomena occur in the 2D transition region between beam and vacuum.
Conclusions:
- Current 1D analytical models are insufficient for 2D emission.
- Enhanced current density "wings" are a significant 2D effect.
- Findings are relevant for designing cathodes with large free electron reservoirs.