INDUSTRY COMPONENT

Focusing Electrode (Wehnelt Cylinder)

A cylindrical electrode in electron guns that controls electron beam focus and current by electrostatic fields.

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Component Specifications

Definition
The Focusing Electrode, commonly known as the Wehnelt Cylinder, is a critical component in electron gun assemblies used in electron microscopes, cathode ray tubes, and electron beam lithography systems. This cylindrical electrode surrounds the cathode and applies a negative bias voltage relative to it, creating an electrostatic field that shapes and focuses the emitted electron beam while regulating beam current. Its precise geometry and voltage control determine the beam's convergence angle, spot size, and stability, directly impacting imaging resolution and system performance.
Working Principle
The Wehnelt Cylinder operates on electrostatic lens principles. By applying a negative voltage relative to the cathode, it creates an equipotential surface that repels electrons, forming a converging electrostatic field. This field focuses diverging electrons from the cathode into a crossover point, controlling both beam convergence and emission current through space-charge effects. The electrode's cylindrical shape and precise positioning optimize field symmetry for uniform focusing.
Materials
High-purity molybdenum, tungsten, or nickel alloys with low outgassing rates, high melting points (>2000°C), and excellent thermal stability. Surface finish: <0.5 μm roughness. Coating: Optional graphite or lanthanum hexaboride for enhanced emission stability.
Technical Parameters
  • Length 10-100 mm
  • Diameter 5-50 mm
  • Voltage Range -50 to -500 V relative to cathode
  • Alignment Tolerance ±0.01 mm
  • Vacuum Compatibility <10^-6 Torr
  • Operating Temperature Up to 1500°C
Standards
ISO 16700, DIN 50300

Industry Taxonomies & Aliases

Commonly used trade names and technical identifiers for Focusing Electrode (Wehnelt Cylinder).

focusing electrode Wehnelt cylinder electron gun component electrostatic focusing electron beam control electron optics cathode assembly Focusing Electrode (Wehnelt Cylinder) Focusing Electrode (Wehnelt Cylinder) in Computer, Electronic and Optical Product Manufacturing

Parent Products

This component is used in the following industrial products

Electron Gun

A device that generates, accelerates, and focuses a beam of electrons for medical radiation therapy applications.

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Engineering Analysis

Risks & Mitigation
  • Thermal deformation altering focus
  • Voltage instability causing beam drift
  • Contamination from outgassing
  • Misalignment degrading resolution
FMEA Triads
Trigger: Material creep at high temperature
Failure: Cylinder deformation changes electrostatic field
Mitigation: Use refractory alloys with creep resistance; implement active cooling
Trigger: Voltage supply ripple
Failure: Beam position instability and focus fluctuation
Mitigation: Install filtered DC power supplies with <0.1% ripple; use feedback stabilization
Trigger: Contamination buildup on surface
Failure: Field distortion and arcing
Mitigation: Regular in-situ cleaning; maintain ultra-high vacuum (<10^-8 Torr)

Industrial Ecosystem

Compatible With

Interchangeable Parts

Compliance & Inspection

Tolerance
±0.005 mm dimensional, ±1% voltage stability
Test Method
Electron beam profiling using Faraday cup arrays; field simulation with finite element analysis

Procurement Evaluation Criteria

Not customer reviews or live demand data. These dimensions support RFQ preparation and supplier evaluation.

Technical documentation
4/5
Manufacturing capability
4/5
Inspection readiness
5/5
Supplier transparency
3/5

These scores are example evaluation dimensions, not real customer ratings, country-specific buyer feedback, or live inquiry activity.

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Frequently Asked Questions

What is the primary function of the Wehnelt Cylinder?

It controls electron beam focus and regulates emission current through electrostatic repulsion, creating the initial crossover point in electron optical systems.

Why are high melting point materials used?

To withstand thermal loads from proximity to the hot cathode and prevent deformation that would alter electrostatic field geometry.

How does voltage affect beam characteristics?

More negative voltage increases beam convergence (smaller spot) but reduces current; optimal settings balance resolution and signal intensity.

Can I contact factories directly?

Yes, each factory profile provides direct contact information.

Data Basis

CNFX manufacturer profiles, technical classification, publicly available product information, and ongoing plausibility checks.

Preliminary Technical Classification
This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

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