| Electron cyclotron resonance heating(ECRH)is one of important auxiliary heating methods for magnetic confinement fusion.It has many significant advantages,such as the easy coupling,strong localization and controllable absorption,and can be used to control the current profile,suppress the MHD activity,and assist plasma start-up.This thesis focuses on the technical requirements of transmission lines for the 140GHz/4MW/100s ECRH system under construction on the EAST facility.The key high-power millimeter wave technologies such as efficient transmission,directional power coupling,wave polarization state controlling and terminal power absorption are studied.The EAST ECRH system employs the over-mode corrugated circular waveguide to transmit the megawatt-scale millimeter wave power from the gyrotron to the quasi-optical launcher.This thesis firstly studies the guided wave theory of the corrugated circular waveguide,introduces the transmission characteristics of electromagnetic waves under the periodic corrugation boundary condition.The field expressions of the mixed modes and linearly polarized modes are provided,and the eigenvalues for them are solved out.Based on the analysis of guided wave theory,the parameter design of circular corrugated waveguide required by EAST ECRH is carried out,and the transmission loss and waveguide exit radiation characteristic of the designed waveguide are calculated and analyzed.The over-mode circular waveguide is prone to mode conversion under non-ideal alignment.The mode conversion causes of corrugated circular waveguide type transmission line are fully analyzed by using mode matching theory,and the relationship between mode conversion loss and transmission line misalignment is deduced.Mode purity detection method based on phase reconstruction algorithm has been developed and demonstrated simulatively.This method can be used to accurately evaluate and improve the ECRH transmission line alignment.In the ECRH experiments,the output power of wave source is required to real-time track to ensure the gyrotron operation safety.The-70dB directional power coupler based on a miter bend structure with the coupling hole array on its reflected mirror is designed.The influence from different hole array coupling strength distributions to whole coupling performance is discussed.The optimal design of two couplers with different hole number 18 and 19 has been completed,and good directivity and in-band flatness are obtained.Based on the design,the directional coupler components are developed.The EAST ECRH system uses second harmonic of the extraordinary mode(X)for heating.Two polarizer mirrors are installed in the transmission line to adjust the wave polarization state to couple the pure X mode in plasma under any beam injection angle.In this thesis,the principle of polarizer mirrors is analyzed by using the vector grating diffraction theory.Both vector integral method and coordinate transformation method are employed to solve the diffraction wave.The design of the polarization rotating mirror and elliptical mirror required by the EAST ECRH system are completed.The low-power test bench is built,and the rotation angle and ellipticity of the designed two polarizer mirrors are tested on this bench.The test results are in agreement with the theoretical values.Afterwards,the polarization requirement of the EAST ECRH experiment is analyzed in detail,and the mathematical relationships between the rotating angles of dual-polarizer,the incidence angle of beam and the X-mode purity in the plasma are calculated,and integrated into a program for operating.The program performance is verified by short-pulse ECRH experiment.At last,the absorption principle of high-power millimeter wave is studied and a cylindrical terminal load is designed.The wave power deposited uniformly on the cylindrical cavity by means of scattering cone mirror and coating dielectric material.The water cooling requirements of the scattering cone and the cylindrical wall are analyzed,and the water cooling channels for two are designed.The cooling effects are verified by analyzing the temperature raise and thermal stress provided one megawatt millimeter wave power loaded. |
PDF Full Text Request