V-band frequency hopping microwave reflectometer in LHD

Area of Science:

• Plasma Physics
• Fusion Energy Research

Background:

• Density fluctuations are crucial for understanding plasma behavior in fusion devices.
• Energetic particle-driven magnetohydrodynamics (MHD) instabilities can impact plasma confinement.

Purpose of the Study:

• To develop and apply a broadband frequency tunable system for measuring internal plasma structure.
• To investigate energetic particle-driven MHD instabilities using advanced reflectometry techniques.

Main Methods:

• Utilized a broadband frequency tunable system with fast and stable frequency hopping capabilities.
• Employed a synthesizer as a hopping source for stable, low phase noise output.
• Multiplied source output to the V-band (50-75 GHz) for plasma measurements in extraordinary mode.
• Implemented heterodyne detection with single sideband frequency modulation for sensitive measurements.

Main Results:

• Successfully scanned the cutoff position over a wide area during plasma discharges.
• Obtained the radial profile of Alfvén eigenmode-like oscillations.
• Demonstrated the system's capability for precise density fluctuation measurements.

Conclusions:

• The developed frequency tunable reflectometer system is effective for studying plasma internal structures.
• The system facilitates the investigation of energetic particle-driven MHD instabilities.
• This technology contributes to a better understanding of plasma dynamics in fusion devices.