The Optimization Design Of LINAC Coupler And Thermal And Structural Analysis

The coupler is an important component in Linac. The traditional single feed coupler cause deflection and degradation of the electron beam properties due to the asymmetry of the electromagnetic field. In this paper, the field asymmetries of the single feed coupler is designed and calculated using the CST Microwave studio. Simulation results show that the contribution of the dipole and quadrupole component of the electric field are 2,711% and 1.583% respectively, and phase deviation are 0.261° and 0.15° respectively. In order to reduce or eliminate the field asymmetries in the coupler cavity, single feed translated (SF-T) geometry are proposed in several laboratories. Simulation results show that when the coupler cavity is moved down by 1.35 mm the asymmetry of the dipole and quadrupole component of the electric field are 0,02% and 0.267% respectively, and the phase deviation are 0.242° and 0.142°, which shows that the field asymmetry is effectively reduced. At the same time, our team proposes an approach used to reduce the field asymmetry of the coupler:single feed loaded with three cylindrical dielectric rods (SF-rods), Simulation results show that the contribution of the dipole and quadrupole component of the electric field are-0.025% and 0.0488% respectively. Compared with SF-T, the new geometry can better reduce amplitude asymmetry of the quadrupole component of electric field.In order to further study the SF-rods in practical application and simulate more efficiently, we perform the analyzation and calculation to the more compact X-band coupler. Then, the electric field asymmetry of SF-T, dual feeding coupler, single feed endowed with short-circuit and SF-rods are designed and calculated. Calculation results show that all of above geometry can reduce the field amplitude asymmetry of the dipole component of electric field. Only the SF-rods quadrupole asymmetry performance is reduced, and the coupler structure is relatively simple.Meanwhile, this paper evaluates the thermal properties of the new coupler structure. We use ANSYS Workbench for simulating several structures thermal field and structure analysis. Simulation results show that thermal loss increases by 1.4% after loading rods compared with traditional coupler. Furthermore, the temperature difference is less than 0.3℃ and directional deformation difference is less than 1.2e-7m. Structural analysis results of the coupler shows that there is no difference in thermal performance between the traditional coupler and the SF-rods. In conclusion,- the new coupler has potential ability to be applied to improve the brightness light source of FEL.