Research On The Matching Network Based On Conjugate-T For ICRF Of EAST

During the EAST experiment,the variation range of strap impedance of the antenna is 1-5?.However,both the characteristic impedance of the transmission line used in the ion cyclotron resonance heating(ICRH)system and the input impedance of the transmitter are 50?.The output power of the transmitter is directly loaded on the current strap of the antenna through the transmission line,which will inevitably lead to the extremely large power coefficient of the system.To solve this mismatch problem,a matching system was designed in EAST,and the original matching device is three liquid stub tuners.Due to historical reasons,three liquid stub tuners is installed far from the antenna.During the EAST experiment,the transmission line between the antenna and the three liquid stub tuners endures a high standing wave voltage,which leads to frequent arcing on the transmission line,and it was difficult to find the arcing position.To address this problem,a new type of matching,called conjugate-T matching,is proposed and installed near the antenna.It is used to assist or replace the three liquid stub tuners to reduce the risk of arcing on the transmission line.The characteristic of the conjugate-T system is that it can make the power of a transmitter load on two straps,and the real part of the input impedance of point T on the two straps are equal,and the imaginary part is opposite.In this thesis,three conjugate-T models are analyzed through numerical and software simulation,including simple conjugate-T system,complex conjugate-T system and direct matching conjugate-T system.Numerical simulation is mainly to conduct a comprehensive analysis of the performance of one conjugate-T system,and software simulation is to analyze the performance of two sets of conjugate-T systems in the presence of power coupling.Through numerical simulations,we can conclude that the difference in the real part of the load in the system has less impact on the reflected power of the system,while the imaginary part of the load will cause dramatic increase in the reflected power of the system.Through software simulation,it is found that the performance of the conjugate-T system is basically maintained in the presence of power coupling,but the between two sets of conjugate-T systems,strong power coupling exists.For this issue,a decoupler is established in the matching network based on conjugate-T.In addition,in order to ensure the normal progress of the conjugate-T experiment,a coaxial switch control system was also developed.Experiments have verified the feasibility of a single directly matched conjugate-T system,but the decoupler established between two conjugate-T systems does not guarantee the smooth work of the two conjugate-T systems in high power mode.Discussion and analysis of the possible causes for this situation has been done,and experimental verification is planned.