Design and development of load resilient mock-up ICRH system of Tokamak with variable load

Author(s): Abhinav Jain

In a magnetic confinement device known as Tokamak, plasma is heated to 100 million ℃ for fusion reaction to take place for future energy generation. Ion cyclotron resonance heating (ICRH) method is used for injecting powerful RF waves into the Tokamak using RF antennae. Plasma offers continuously variable mismatched load. These variations are very difficult to match and to a certain extent developed matching networks are failed to cope with faster variation of plasma impedance. As the real ICRH system of Tokamak spread over long area and not suitable for changes required for research and development. Therefore, mock-up ICRH has planned with objective to develop a prototype for the load resilient ICRH system. So, the size of the mock-up has been reduced by scaling the design at higher frequency and at lower power, without affecting its performance, so that it can be implemented at a single test bench. Low power mock-up ICRH system as shown in Fig. 1 comprises of various components such as a 3dB hybrid coupler, co-axial transmission lines, directional coupler, matching network, RF antennae, variable water load etc. These components are indigenously designed, developed and scaled at five times ICRH frequency i.e. 182.5 MHz. The matching network consists of motorized variable stub tuner, line stretcher, service stubs, etc. which are used to transform the plasma impedance in real time. The components have been simulated, optimized for better results and then fabricated with rigid co-axial transmission line providing the power capability up to 2kW. The test response of each component has been presented and compared with the simulated results and found in good agreement. The developed mock-up has been optimized and tested for highly efficient, load resilient fast matching network. Each component has an important application in the field of radar, satellite, radio communication and broadcasting etc.