Research On Impedance Characteristics And Matching Tuning Of High Power RF Ion Source

In a magnetic confinement controllable nuclear fusion reactor,the plasma needs to be heated to a temperature of about 100 million degrees to achieve nuclear fusion.The neutral beam injection heating system is one of the auxiliary heating methods of tokamak and other controllable nuclear fusion devices,and it is also the most effective heating method.The inductively coupled radio frequency ion source has become the first choice for neutral beam ion sources in the future due to its maintenance-free,long life,and non-polluting to plasma.The impedance matching network is an important part of the RF(radio frequency)ion source power feeding system.The impedance matching network transforms the load(i.e.,excitation coil)impedance to be consistent with the characteristic impedance of the transmission line and the power supply,thereby achieving maximum power transmission and suppressing RF power reflection.In the design process of impedance matching network,it is necessary to calculate the parameters of the matching network according to the equivalent parameters of the radio frequency ion source.In this article,a 10 k W,2 MHz argon discharge ion source experimental platform was first introduced and focusing on the design method of the impedance matching network.At the same time,with the help of the experimental platform,the measurement of the equivalent impedance of the excitation coil of the radio frequency ion source was successfully carried out.The feasibility of the coupling coil equivalent impedance measurement theory was determined.The RF power coupling efficiency measured before the matching network was compared with the RF power coupling efficiency measured before the coil.Secondly,the equivalent impedance of the RF ion source excitation coil under different conditions was estimated with analytical methods and the finite element model which was based on the plasma fluid model.The two calculation methods have good consistency in the results.And the analytical method can be fast but a rough estimate of the equivalent impedance of the excitation coil was obtained.The finite element model based on the plasma fluid model could accurately calculate the change trend of the equivalent impedance of the coupling coil,but the calculation period is longer.Based on the calculation results of the equivalent impedance of the excitation coil of the radio frequency ion source,a preliminary design of the matching network of the dual-drive radio frequency ion source was carried out,including the distribution range of the impedance matching network capacitance and the capacity parameters of the capacitance.The feasibility of capacitance tuning and frequency tuning was confirmed.After that,the advantages and disadvantages of each method were analyzed.Finally,it was found that the capacitance tuning was more accurate,and the frequency tuning has the advantages of faster and more concise remote control.Take the advantages of each other,the combination of the two tuning method can be used as a dual-drive or multi-drive matching tuning method of radio frequency ion source in the future.