Study On Key Technology And Experiment Of Power Feed-in For High Power RF Ion Source

The Neutral Beam Injection(NBI)is the mostly effectively plasma heating method for fusion plasma.The requirements of NBI was increased from low power with shot pulse to high power with long pulse,even steady-state operation with the development of fusion research.The Radio Frequency(RF)ion source has the advantage of long pulse operation and was selected as preferred source for high power NBI system.As one of the key parts for stable plasma discharge,the RF power feed-in system is used to transfer the RF power into the ion source.In order to solve the power feed-in problem existing in the operation of high-power RF ion source,the key technology and corresponding experimental research of high-power RF power feed-in system is carried out.It is of great significance to the development of RF ion source.In this paper,the principle and characteristic of RF power transmission system of RF ion source was studied according to the structure of high-power RF power feed-in system.Combined with discharge principle of RF ion source,the simulation of RF plasma discharge was studied by means of simulation software and the variation tendency of average electron density with the increase of RF power is obtained.The impedance characteristic of RF driver was analyzed used the classical theory of transformer mode,the variation tendency of equivalent impedance with the density of electron is obtained and the result lays the theoretical foundation for the key technology study of RF power feed-in system.The key technologies of RF power feed-in system was studied based on the theory analysis of power feed-in system characteristic.Firstly,the impedance matching network was designed and the main parameters of matching network were calculated.Secondly,a matching network with high voltage transformer was designed for the RF power isolating transmission.The test results show that the static withstand voltage reaches the 200kVDC and transfer efficiency is greater than 95%,it is satisfied with the requirements of the DC high-voltage isolation and RF power transfer.Thirdly,the variation tendency of the capacitance parameters of impedance matching network with the equivalent impedance of driver is analyzed,it can direct the design of impedance matching network and the optimum matching tuning in the experiment.Lastly,the impedance matching network is simulated using simulation tool and the feasibility of design and veracity of main parameter are verified.Based on the design of analysis of key technology of RF power feed-in system the RF power feed-in system was developed and the corresponding experiment is carried out.In order to solve the problems of difficult plasma ignition and large reflected power during ignition,the methods of high gas pressure and starter filament auxiliary are proposed.Aiming at the large reflected power caused by the impedance detuning at the time of plasma ignition,the discharge controlling method of RF power climbing output is put forward and realize the stable plasma discharge at high power.In the plasma discharge experiment,the change trend of equivalent impedance of the driver with the electron density is obtained through the optimum impedance matching scanning analysis,which verifies the accuracy of the theoretical analysis results.On this basis,50kW high power,47kW/1000s long pulse stable plasma discharge was obtained.The experimental results show that the high power RF ion source power feed-in system is reasonable and feasible,which can meet the requirements of high power RF ion source to carry out physical experiments.