Development of Mock-Up RF Matching Network for ICRH System of Tokamak and Its Optimization with Continuously Variable Load

Abstract

In Tokamaks, RF power of few MW is feed to the ICRH antenna for heating the plasma for the fusion reaction. The plasma offers continuously variable load impedance, which changes dynamically with time. These variations are mainly due to the collective effect of the spatial change of plasma density and Edge Localized Modes (ELMs) inside the tokamak. These variations might be in the order of few milliseconds. Such fast variations are very difficult to match, and to a certain extent, developed matching networks fail to cope-up with the faster variation of the plasma load impedance. Therefore, the development of a matching network is inevitable to match the fast variation of plasma. The real ICRH systems of the tokamaks are spatially distributed in very long distances and unreliable for implementation of the research problem. Therefore, the idea is to develop a mock-up of the ICRH system on the test bench. To reduce the size of the mock-up, and make it accommodate at the test bench, the mock-up is designed for lower power handling capability and scaled at five times the ICRH frequency. Now, the mock-up can be a useful set-up on a single test bench where research problems related to the ICRH system of Tokamak can be tested before final implementation. The proposed work has been completed in several stages which are briefed as follow:  The components of the mock-up ICRH system, such as 3dB hybrid coupler, directional couplers, rigid coaxial tapped transmission line, coaxial stub tuners, line stretcher, RF antenna, variable water load has been developed. Since these component designs are novel in many respects, it is a part of our research objective.  The developed components of the mock-up have been integrated as in the similar layout of the ICRH system and tested using VNA for the desired performance.  A computational program has been developed with a defined control sequence to control the detectors and matching components. The developed system has been optimized for the best possible speed using the developed program.  The developed system is capable of automatically match any arbitrary load and tested for load resilient behavior as per our thesis objective.