Solenoid Field Emission Cathode for Focused High-Current Beams
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Solution Overview
Problem
Existing field emission cathode devices struggle to achieve stable high current while maintaining a small and focused electron beam cross-section, particularly for cathodes with large emission areas, and they often fail to protect the cathode from ion bombardment.
Innovation Solution
A field emission cathode device comprising a cylindrical substrate with field emission material, a solenoid extending concentrically around the cathode, and a magnetic field generated by a constant DC current in the solenoid, which interacts with an electric field to induce electron emission and spiral motion within the gap, focusing the electron beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large-area cathode is used to achieve stable high current, then the total current emission is improved, but the electron beam cross-section becomes large and difficult to focus
Solution Approach 1:
The cathode is segmented into multiple independent emission regions arranged in a specific geometric pattern (e.g., tetrahedral configuration with multiple vertices). Each segment emits electrons independently, and the magnetic field guides electrons from different segments to converge at different focal points, allowing the large total emission area to produce multiple small focused beams rather than one large diffuse beam.
Solution Approach 2:
The invention transitions from a planar 2D cathode surface to a 3D spatial arrangement of emission points. By positioning emission sites at different spatial locations (e.g., vertices of a tetrahedron) and using magnetic field lines that spiral through three-dimensional space, electrons from a large-area cathode can be focused to small cross-sections in a different dimensional plane, effectively decoupling emission area from beam cross-section.
2Reliability
If a large-area cathode is used to achieve stable high current, then the current stability is improved, but the device complexity increases due to focusing requirements
Solution Approach 1:
The magnetic field generation system serves multiple functions simultaneously: it provides the primary electron extraction field, guides electron trajectories, focuses electrons to small cross-sections, and protects the cathode from ion bombardment. This multi-functionality eliminates the need for separate focusing coils or additional complexity, as the same magnetic field structure accomplishes multiple critical tasks.
Solution Approach 2:
The invention merges the field emission extraction function with the electron focusing function into a single magnetic field system. The magnetic field that extracts electrons from the cathode surface is the same field that guides and focuses them, combining what would traditionally require separate mechanisms into one integrated system, thereby reducing overall device complexity.
3Productivity
If a conventional field emission cathode is used, then the electron emission is achieved, but the cathode is vulnerable to ion bombardment damage
Solution Approach 1:
The invention converts the potentially harmful ion bombardment into a beneficial protective mechanism. By configuring the magnetic field to create a spiraling electron trajectory that forms a protective envelope around the cathode, the same magnetic field that enables electron emission also deflects ions away from the cathode surface, turning a vulnerability into a protective feature.
Solution Approach 2:
The magnetic field is configured in advance to create a protective barrier around the cathode before ion bombardment can occur. The spiraling electron paths form a preemptive shield that deflects ions away from the cathode surface, preventing damage before it can happen rather than attempting to mitigate damage after it occurs.
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 device achieves stable high current emission while forming a small and focused electron beam cross-section, and the magnetic field constrains electrons to protect the cathode from ion bombardment.
Implementation Method 1
a current source (V1) electrically connected to the solenoid and arranged to direct a constant polarity (DC) current (I) thereto, the DC current (I) in the solenoid forming a magnetic field (B) along the solenoid
Implementation Method 2
a gate voltage source (VG) electrically connected to the solenoid or the field emission cathode and arranged to interact therewith to generate an electric field (E) inducing the field emission cathode to emit electrons (e) from the field emission material into the gap
Implementation Method 3
the emitted electrons being responsive to the magnetic field to spiral within the gap and about the longitudinal axis, in correspondence with the current flow in the solenoid
Data Source
AI summary
A field emission cathode device comprises a field emission cathode including a cylindrical substrate and a field emission material deposited on a cylindrical surface thereof. The field emission cathode defines a longitudinal axis. A solenoid extends concentrically about the cylindrical surface, and defines a gap therebetween. The solenoid defines opposed open ends perpendicular to the longitudinal axis. A current source directs a constant polarity (DC) current to the solenoid, that forms a magnetic field along the solenoid. A gate voltage source electrically connected to the solenoid or the field emission cathode interacts therewith to generate an electric field inducing the field emission cathode to emit electrons from the field emission material into the gap. The emitted electrons are responsive to the magnetic field to spiral within the gap and about the longitudinal axis, in correspondence with the current flow in the solenoid, through the first open end of the solenoid.