Phase noise compensation in long-distance microwave reflectometry for fusion reactors using coherence signal techniques

Abstract Microwave reflectometry serves as a critical diagnostic tool for plasma analysis in magnetic confinement fusion devices. However, phase noise originating from Voltage-Controlled Oscillators (VCOs) severely degrades measurement accuracy, particularly in systems with extended transmission paths. This study explores the impact of VCO-induced phase noise on Frequency-Modulated Continuous-Wave reflectometry and proposes a novel coherence signal-based compensation method. By leveraging dual time-of-flight signals with known and adjustable delays, the system effectively reduces phase noise, as demonstrated through experimental validation. The proposed technique significantly enhances stability and precision, especially in scenarios requiring high temporal resolution and rapid frequency sweeps, positioning it as a pivotal solution for next-generation fusion reactors such as International Thermonuclear Experimental Reactor (ITER) and Burning plasma Experimental Superconducting Tokamak (BEST).