Virtual Critical Coupling in High-Power Resonant Systems

TL;DR

This paper introduces Virtual Critical Coupling, a novel method for reducing power reflections in high-power resonators, enhancing efficiency and stability in applications like fusion energy systems.

Contribution

We propose a complex frequency excitation technique that minimizes reflections in high-power resonators without mechanical modifications, demonstrated through high-power experiments.

Findings

Ninefold reduction in reflection coefficients at high power

Efficient energy storage with tailored complex frequency signals

Potential improvements in fusion energy system stability

Abstract

Exciting high-power resonators pose challenges such as managing power reflections, which can cause energy losses and damage system components. This is crucial for applications like Lower Hybrid Current Drive (LHCD) systems in tokamaks, where plasma stability and confinement depend on efficient energy transfer. In this work, we introduce the Virtual Critical Coupling mechanism to address reflection-related challenges in S-band resonators. We theoretically designed a complex frequency excitation signal tailored to the resonator's characteristics, facilitating efficient energy storage and minimizing reflections without mechanical modifications. Using a custom low-level RF system, we conducted experiments at 32 mW and 600 kW with a 5 MW S-band klystron, demonstrating a ninefold reduction in reflection coefficients compared to traditional monochromatic excitation in high-power tests. This approach enhances the efficiency and stability of high-power resonant systems, potentially advancing nuclear fusion energy production.