In-situ frequency calibration of frequency modulated continuous wave reflectometry

Area of Science:

• Plasma physics
• Fusion energy research
• Microwave diagnostics

Background:

• Frequency modulated continuous wave (FMCW) reflectometers are crucial for measuring plasma density profiles in fusion devices like the KSTAR tokamak.
• Accurate density profile reconstruction relies heavily on precise frequency calibration of the reflectometer system.
• Existing calibration methods may not achieve the necessary accuracy for rapid, time-resolved measurements.

Purpose of the Study:

• To develop and validate novel in situ frequency calibration techniques for FMCW reflectometers.
• To enhance the accuracy of plasma density profile measurements in the KSTAR tokamak.
• To enable precise real-time frequency determination during fast (20 μs) sweep times.

Main Methods:

• Development of two novel in situ frequency calibration techniques.
• Technique 1: Analysis of the intermediate frequency (IF) signal using wavelet transform with a known local oscillator (LO) frequency.
• Technique 2: Calibration by measuring reflectometer output with varying delay lines to eliminate system group delay.

Main Results:

• Successful implementation of two distinct methods for in situ frequency calibration.
• Demonstration of accurate frequency determination during the 20 μs sweep time.
• Comparison of results obtained from both calibration techniques.

Conclusions:

• The developed wavelet transform and delay line methods provide accurate in situ frequency calibration for FMCW reflectometers.
• These techniques are essential for improving the precision of plasma density profile measurements in tokamaks.
• The findings contribute to more reliable diagnostics for fusion energy research.