Center conductor diagnostic for multipactor detection in inaccessible geometries.

Area of Science:

• Physics
• Electrical Engineering
• Plasma Science

Background:

• Electron collecting current probes are standard for diagnosing multipactor and RF ionization breakdown.
• Existing methods are limited to physically accessible breakdown regions.

Purpose of the Study:

• To present techniques for measuring multipactor current directly on the center conductor of coaxial RF devices.
• To enable global multipactor detection with enhanced sensitivity.

Main Methods:

• Developed a center conductor diagnostic for multipactor current measurement in coaxial and two-conductor RF systems.
• Investigated the impact of DC bias on the breakdown threshold in both coaxial and parallel plate geometries.
• Utilized AC coupling for systems with low DC impedance.

Main Results:

• The center conductor diagnostic provides improved sensitivity and global detection compared to phase null, third harmonic, and reflected power methods.
• DC bias effects on breakdown threshold were quantified: <1 dB change for VDC/VRF0<0.8 in coaxial and <1 dB for VDC/VRF0<0.2 in parallel plates.
• The diagnostic functions effectively with no bias, though biases of 0-10V can be applied if needed.

Conclusions:

• The center conductor diagnostic is a reliable and sensitive method for global multipactor detection in RF systems.
• The study quantifies DC bias effects, establishing guidelines for its application without significantly altering breakdown thresholds.
• The polarity of the current signal indicates net electron collection or emission, providing further diagnostic information.