W-band tunable, multi-channel, frequency comb Doppler backscattering diagnostic in the ASDEX-Upgrade tokamak

Area of Science:

• Plasma physics
• Fusion energy research
• Diagnostic techniques

Background:

• Tokamak devices are crucial for fusion energy research.
• Accurate plasma diagnostics are essential for understanding and controlling fusion reactions.
• Advanced diagnostic tools are needed to capture dynamic plasma behaviors.

Purpose of the Study:

• To introduce a novel, flexible, multi-channel frequency comb Doppler backscattering diagnostic.
• To detail its design, implementation, and initial data acquisition.
• To demonstrate its capability in measuring plasma dynamics during confinement transitions.

Main Methods:

• Utilized a double side-band signal and a frequency multiplier to create a multi-frequency output.
• Employed a two-step frequency down-conversion and I/Q demodulation for signal measurement.
• Enabled remote tuning of the frequency comb spectrum (W-band) and inter-frequency separation (0.1–6 GHz).

Main Results:

• Successfully implemented and operated a multi-channel, frequency comb Doppler backscattering diagnostic.
• Achieved simultaneous measurement of seven distinct backscattered frequencies with >30 dB signal.
• Captured time evolution of signals during an L-to-H-mode confinement transition.

Conclusions:

• The developed diagnostic is a flexible and powerful tool for tokamak plasma research.
• It provides valuable, high-resolution data on plasma behavior during confinement transitions.
• This technology advances the capability for real-time plasma monitoring and control.