Design And Experimental Study Of EAST Curved ICRH Antenna

Ion cyclotron resonance heating（ICRH）is a key auxiliary heating means on EAST,and the antenna is a key component of the ICRH system,which not only has to carry megawatt high power,but also has to satisfy the long-pulse and steady state operation.In this paper,a new antenna is designed for the low coupling problem caused by the low density of plasma at the antenna port on EAST,as well as the problem of heat dissipation on the antenna’s faraday screen,in order to improve the antenna’s coupling efficiency and engineering safety.The new ICRH antenna is designed and optimized by theoretical calculations and multi-physics field finite element analysis,and the fabrication of the new antenna is completed,meanwhile,the antenna is verified by high-power and longpulse experiments on EAST.Since the plasma boundary density at the antenna port measured on the EAST is 5×10¹⁸ m^-3,which is lower than the cutoff density of the ICRH antenna,resulting in the low coupling efficiency of the original antenna with the plasma,a new ICRH antenna needs to be designed in order to improve the coupling efficiency of the antenna with the plasma.The optimal value of the power spectrum of the ICRH antenna is obtained by numerical calculations as k//～7^-9 m^-1.In addition,COMSOL electromagnetic simulation software combined with the RAPCASOL analysis platform is used to construct the physical model of the antenna,and the geometrical dimensions and key parameters of the antenna are optimized and designed,finally the dimensions and positions of the plasma-facing-components of the antenna（faraday screen and current straps）are determined by increasing the coupling impedance and satisfying the maximum electric field strength condition.Compared with the original antenna,the coupling impedance of the newly designed antenna is improved by nearly three times under the same plasma parameters.In order to ensure the safety and stability of the antenna engineering structure,the new antenna was analyzed and optimized for engineering design based on the above dimensional parameters of the ICRH antenna.With the rise of the level of manufacturing process and the demand of high-power and long-pulse of EAST experiments,the engineering structure of the antenna is required to be higher,for this reason,the faraday screen and the current straps surface are designed to be in the form of threedimensional curved surface that is consistent with the outermost magnetic surface of the plasma,which ensures that the antenna structure can better match the shape of the outermost magnetic surface no matter in the poleward or the ringward direction and improves the antenna coupling homogeneous,at the same time,the chance of ablation of the faraday screen surface due to distance inhomogeneity is also greatly reduced.In terms of antenna water-cooling flow path,the flow paths of the current straps and faraday screen are optimized to meet the requirements of uniform flow distribution and the pressure difference between the inlet and outlet of the flow paths is less than the rated working pressure of the system.In terms of thermal analysis,the heat of plasma irradiation and the heat of radio-frequency loss are considered as the heat source applied to the corresponding surfaces of the faraday screen and the current straps at the same time and the convective heat transfer coefficients obtained from the design of water-cooling flow channel are used for the fluid-heat coupling analysis,the antenna surface temperature is uniformly distributed and meets the heat dissipation requirements under high-power and long-pulse conditions.In terms of electromagnetic force analysis,due to the plasma rupture,a great induced current will be induced on the ICRH antenna,and the antenna will be subjected to strong electromagnetic force under the background magnetic field,for this reason,the electromagnetic force on the faraday screen and the current straps of the ICRH antenna is calculated and analyzed,and the final maximum electromagnetic force on the faraday screen is obtained to be 900 N,and the maximum electromagnetic force on the current straps is obtained to be 40 N,which meets the antenna design requirements.In terms of structural analysis,the ICRH antenna needs to be structurally analyzed under composite loads such as electromagnetic force and thermal stress to verify whether its displacement and stress meet the design requirements and to assess its safety and reliability.After calculation and analysis,it is confirmed that the antenna structure meets the design requirements.In terms of transmission line design,since the antenna impedance is only a few ohms and the characteristic impedance of the transmission line is 50Ω,a high standing wave voltage will be formed between the antenna and the stub tuner under high power operation conditions,which will result in the risk of the transmission line arcing.In order to increase the input impedance and to reduce the standing wave voltage on the transmission line,the impedance transformer position is designed and optimized,the optimal position is finally obtained by analyzing,and the results show that the input impedance is significantly improved and the transmission line standing wave voltage is significantly reduced.The ICRH antenna designed in this paper has been evaluated in several rounds of experiments,and the long-pulse and high-power experiments have been completed.The surface temperature of the ICRH antenna is uniformly distributed,as observed by the infrared camera.The high power experiments show that the heating efficiency of the ICRH antenna increases five times,and the plasma energy storage increment is 35 kJ/MW,the coupling efficiency and the heating efficiency are significantly improved,which verifies the reliability and feasibility of the ICRH antenna designed in this paper.This research results are important references for the design of ICRH antenna for future fusion reactors.