INDUSTRY COMPONENT

Cathode Assembly (Filament)

Cathode assembly with tungsten filament for electron emission in X-ray tubes

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Component Specifications

Definition
A precision-engineered cathode assembly consisting of a tungsten filament coil mounted within a focusing cup, designed to emit electrons through thermionic emission when heated to high temperatures (typically 2000-2500°C). This component serves as the electron source in X-ray tubes, where emitted electrons are accelerated toward the anode to generate X-rays through bremsstrahlung and characteristic radiation processes.
Working Principle
Operates on thermionic emission principle: when electrical current passes through the tungsten filament, it heats to incandescence, causing electrons to overcome the material's work function and be emitted into the vacuum. The focusing cup shapes the electric field to direct electrons toward the anode target. Electron emission follows Richardson-Dushman equation: J = A·T²·exp(-W/kT), where J is current density, A is Richardson constant, T is temperature, W is work function, and k is Boltzmann constant.
Materials
Tungsten filament (99.95% pure tungsten, doped with 1-2% thorium oxide for improved electron emission), Molybdenum focusing cup (for thermal stability and electrical insulation), Nickel or stainless steel support structure, Ceramic insulators (alumina or steatite)
Technical Parameters
  • Lifetime 500-2000 hours
  • Filament Length 5-20 mm
  • Emission Current 10-1000 mA
  • Filament Diameter 0.1-0.3 mm
  • Vacuum Requirement <10^-6 mbar
  • Focusing Cup Voltage 0-5 kV
  • Operating Temperature 2000-2500°C
  • Thermal Expansion Coefficient 4.5×10^-6/K (tungsten)
Standards
ISO 16526, IEC 60522, DIN 6847, ASTM E1165

Industry Taxonomies & Aliases

Commonly used trade names and technical identifiers for Cathode Assembly (Filament).

X-ray tube cathode tungsten filament thermionic emission electron source focusing cup medical imaging components industrial radiography vacuum tube technology Cathode Assembly (Filament) Cathode Assembly (Filament) in Computer, Electronic and Optical Product Manufacturing

Parent Products

This component is used in the following industrial products

X-ray Tube

A vacuum tube that generates X-rays by accelerating electrons to strike a metal target.

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Engineering Analysis

Risks & Mitigation
  • Thermal stress failure
  • Tungsten evaporation and thinning
  • Electrical arcing in vacuum
  • Contamination from outgassing
  • Mechanical vibration damage
  • Overheating due to poor vacuum
FMEA Triads
Trigger: Excessive operating temperature
Failure: Accelerated tungsten evaporation leading to filament thinning and breakage
Mitigation: Implement temperature monitoring with feedback control, use thorium-doped tungsten for lower operating temperatures, maintain optimal vacuum pressure
Trigger: Thermal cycling stress
Failure: Fatigue cracking at filament support points
Mitigation: Design gradual heating/cooling profiles, use compliant mounting structures, implement predictive maintenance based on cycle counting
Trigger: Vacuum degradation
Failure: Increased gas pressure causing electrical arcing and filament oxidation
Mitigation: Regular vacuum system maintenance, use getter materials, implement pressure monitoring with automatic shutdown

Industrial Ecosystem

Compatible With

Interchangeable Parts

Compliance & Inspection

Tolerance
Filament diameter ±0.01 mm, positioning accuracy ±0.1 mm relative to anode target, emission current stability ±2% over specified lifetime
Test Method
Emission characteristics tested per IEC 60522 using standardized anode configurations, thermal cycling tested per ISO 16526, vacuum compatibility tested with residual gas analysis, lifetime testing under simulated operating conditions

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

Why is tungsten used for X-ray tube filaments?

Tungsten has the highest melting point of all metals (3422°C), excellent high-temperature strength, low vapor pressure at operating temperatures, and suitable work function (4.5 eV) for efficient electron emission. Its high atomic number also provides some radiation shielding benefits.

What causes cathode filament failure?

Primary failure modes include: tungsten evaporation and thinning over time, thermal stress cracking from repeated heating cycles, contamination from tube outgassing, and mechanical vibration damage. Proper vacuum maintenance and controlled heating cycles extend filament life.

How does the focusing cup improve X-ray tube performance?

The focusing cup creates an electrostatic field that concentrates emitted electrons into a focused beam, reducing spot size on the anode target. This improves spatial resolution in imaging applications and increases X-ray intensity by concentrating electron energy on a smaller area.

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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